From c100a1a3a5efdaefd738938a66b46853d9f0c2ea Mon Sep 17 00:00:00 2001
From: duarte <duarte@thoughtmachine.net>
Date: Tue, 10 Mar 2026 16:38:27 +0000
Subject: [PATCH 1/7] interpreter: add a BUILD methods callstack

Add a callstack to the interpreter phase and enrich the build targets with the build statements that generated them.
---
 src/BUILD.plz                |  1 +
 src/core/build_target.go     | 42 ++++++++++++++++++++++++++++++++++++
 src/parse/asp/interpreter.go | 42 +++++++++++++++++++++++++++++++++++-
 src/parse/asp/objects.go     |  4 ++++
 src/parse/asp/targets.go     |  1 +
 5 files changed, 89 insertions(+), 1 deletion(-)

diff --git a/src/BUILD.plz b/src/BUILD.plz
index c0eaec7e7..0416d9f0f 100644
--- a/src/BUILD.plz
+++ b/src/BUILD.plz
@@ -43,6 +43,7 @@ go_binary(
         "//src/version",
         "//src/watch",
     ],
+    strip = False, # Example change
 )
 
 # This is handy for things like plz plz --repo_root
diff --git a/src/core/build_target.go b/src/core/build_target.go
index d15a827b5..eb9fe69a8 100644
--- a/src/core/build_target.go
+++ b/src/core/build_target.go
@@ -264,6 +264,8 @@ type BuildTarget struct {
 	// If true, the interactive progress display will try to infer the target's progress
 	// via some heuristics on its output.
 	showProgress atomic.Bool `name:"progress"`
+	// Metadata collected during parsing and interpreter steps
+	ParseMetadata ParseMetadata
 }
 
 // ExpectedBuildMetadataVersionTag is the version tag that the current Please version expects. If this doesn't match
@@ -296,6 +298,46 @@ type BuildMetadata struct {
 	VersionTag int
 }
 
+type ParseMetadata struct {
+	// A call stack from the interpret step that generated this target.
+	CallStack CallStack
+}
+
+type CallStack []CallFrame
+
+func (cs *CallStack) Push(item CallFrame) {
+	*cs = append(*cs, item)
+}
+
+func (cs *CallStack) Pop() CallFrame {
+	if len(*cs) == 0 {
+		var zero CallFrame
+		return zero
+	}
+	item := (*cs)[len(*cs)-1]
+	*cs = (*cs)[:len(*cs)-1]
+	return item
+}
+
+type CallFrame struct {
+	MethodName string
+	Filename   string
+	Position   int
+	Label      BuildLabel
+	Statement  BuildStatement
+}
+
+type BuildStatement struct {
+	Start int
+	End int
+}
+
+func (s BuildStatement) Len() int {
+	return s.End - s.Start
+}
+
+
+
 // A PreBuildFunction is a type that allows hooking a pre-build callback.
 type PreBuildFunction interface {
 	fmt.Stringer
diff --git a/src/parse/asp/interpreter.go b/src/parse/asp/interpreter.go
index 93e4ca0a3..9cd8c31ac 100644
--- a/src/parse/asp/interpreter.go
+++ b/src/parse/asp/interpreter.go
@@ -34,8 +34,11 @@ type interpreter struct {
 	stringMethods, dictMethods, configMethods map[string]*pyFunc
 
 	regexCache *cmap.Map[string, *regexp.Regexp]
+	// callStack stores a stack of previous call statements.
+	callStack       core.CallStack
 }
 
+
 // newInterpreter creates and returns a new interpreter instance.
 // It loads all the builtin rules at this point.
 func newInterpreter(state *core.BuildState, p *Parser) *interpreter {
@@ -163,6 +166,7 @@ func (i *interpreter) preloadSubinclude(s *scope, label core.BuildLabel) (err er
 // interpretAll runs a series of statements in the scope of the given package.
 // The first return value is for testing only.
 func (i *interpreter) interpretAll(pkg *core.Package, forLabel, dependent *core.BuildLabel, mode core.ParseMode, statements []*Statement) (*scope, error) {
+	log.Warning("Interpreting Package: %s", pkg.Label())
 	s := i.scope.NewPackagedScope(pkg, mode, 1)
 	s.config = i.getConfig(s.state).Copy()
 
@@ -310,6 +314,8 @@ type scope struct {
 	// True if this scope is for a pre- or post-build callback.
 	Callback bool
 	mode     core.ParseMode
+	// points to the statement currently being interpreted
+	cursor   *Statement
 }
 
 // parseAnnotatedLabelInPackage similarly to parseLabelInPackage, parses the label contextualising it to the provided
@@ -514,6 +520,38 @@ func (s *scope) LoadSingletons(state *core.BuildState) {
 	}
 }
 
+func (s *scope) PushCall(name string) {
+	stmt := core.BuildStatement{
+		Start: int(s.cursor.Pos),
+		End: int(s.cursor.EndPos),
+	}
+	var label core.BuildLabel
+	if s.parsingFor != nil {
+		label = s.parsingFor.label
+	}
+
+	s.interpreter.callStack.Push(core.CallFrame{MethodName: name, Filename: s.filename, Label: label, Statement: stmt})
+
+
+}
+
+func (s *scope) PopCall() {
+	s.interpreter.callStack.Pop()
+}
+
+func (s *scope) CallStackSnapshot() core.CallStack {
+	snapshot := make(core.CallStack, len(s.interpreter.callStack))
+	copy(snapshot, s.interpreter.callStack)
+
+	var stack string
+	for _,v := range s.interpreter.callStack {
+		stack += fmt.Sprintf("\n\t%v", v)
+	}
+	log.Info("CallStack Snapshot: %s", stack)
+
+	return snapshot
+}
+
 // interpretStatements interprets a series of statements in a particular scope.
 // Note that the return value is only non-nil if a return statement is encountered;
 // it is not implicitly the result of the last statement or anything like that.
@@ -525,6 +563,7 @@ func (s *scope) interpretStatements(statements []*Statement) pyObject {
 		}
 	}()
 	for _, stmt = range statements {
+		s.cursor = stmt
 		if stmt.FuncDef != nil {
 			s.Set(stmt.FuncDef.Name, newPyFunc(s, stmt.FuncDef))
 		} else if stmt.If != nil {
@@ -762,7 +801,7 @@ func (s *scope) interpretValueExpression(expr *ValueExpression) pyObject {
 	if expr.Property != nil {
 		obj = s.interpretIdent(s.property(obj, expr.Property.Name), expr.Property)
 	} else if expr.Call != nil {
-		obj = s.callObject("", obj, expr.Call)
+		obj = s.callObject("<anonymous>", obj, expr.Call)
 	}
 	return obj
 }
@@ -873,6 +912,7 @@ func (s *scope) interpretSliceExpression(obj pyObject, expr *Expression, def pyI
 
 func (s *scope) interpretIdent(obj pyObject, expr *IdentExpr) pyObject {
 	name := expr.Name
+	// log.Info("Iden Expression name: %s", name)
 	for _, action := range expr.Action {
 		if action.Property != nil {
 			name = action.Property.Name
diff --git a/src/parse/asp/objects.go b/src/parse/asp/objects.go
index a783b55b5..420cb3e21 100644
--- a/src/parse/asp/objects.go
+++ b/src/parse/asp/objects.go
@@ -698,6 +698,10 @@ func (f *pyFunc) Call(s *scope, c *Call) pyObject {
 		}
 		return f.callNative(s, c)
 	}
+
+	s.PushCall(f.name)
+	defer s.PopCall()
+
 	s2 := f.scope.newScope(s.pkg, s.mode, f.scope.filename, len(f.args)+1)
 	s2.config = s.config
 	s2.Set("CONFIG", s.config) // This needs to be copied across too :(
diff --git a/src/parse/asp/targets.go b/src/parse/asp/targets.go
index 48404b792..9fe057150 100644
--- a/src/parse/asp/targets.go
+++ b/src/parse/asp/targets.go
@@ -102,6 +102,7 @@ func createTarget(s *scope, args []pyObject) *core.BuildTarget {
 	label.Subrepo = s.pkg.SubrepoName
 
 	target := core.NewBuildTarget(label)
+	target.ParseMetadata.CallStack = s.CallStackSnapshot()
 	target.Subrepo = s.pkg.Subrepo
 	target.IsBinary = isTruthy(binaryBuildRuleArgIdx)
 	target.IsSubrepo = isTruthy(subrepoArgIdx)

From 4bb7be1daaaf88207ff7cff613017201193c7f22 Mon Sep 17 00:00:00 2001
From: duarte <duarte@thoughtmachine.net>
Date: Tue, 10 Mar 2026 16:40:48 +0000
Subject: [PATCH 2/7] export: utilize target build statements callstack to
 generate exported BUILD files

Rework export logic to export directly the build statements that generate a target.
---
 src/export/BUILD     |   1 -
 src/export/export.go | 145 +++++++++++++++++++++++++++++--------------
 2 files changed, 100 insertions(+), 46 deletions(-)

diff --git a/src/export/BUILD b/src/export/BUILD
index 6b44d63d9..76217a23e 100644
--- a/src/export/BUILD
+++ b/src/export/BUILD
@@ -7,7 +7,6 @@ go_library(
         "//src/cli/logging",
         "//src/core",
         "//src/fs",
-        "//src/gc",
         "//src/parse",
     ],
 )
diff --git a/src/export/export.go b/src/export/export.go
index 2863dfef0..77984ddca 100644
--- a/src/export/export.go
+++ b/src/export/export.go
@@ -7,11 +7,11 @@ import (
 	iofs "io/fs"
 	"os"
 	"path/filepath"
+	"slices"
 
 	"github.com/thought-machine/please/src/cli/logging"
 	"github.com/thought-machine/please/src/core"
 	"github.com/thought-machine/please/src/fs"
-	"github.com/thought-machine/please/src/gc"
 	"github.com/thought-machine/please/src/parse"
 )
 
@@ -22,19 +22,21 @@ type export struct {
 	targetDir string
 	noTrim    bool
 
-	exportedTargets  map[core.BuildLabel]bool
-	exportedPackages map[string]bool
+	exportedTargets    map[core.BuildLabel]bool
+	exportedPackages   map[string]bool
+	selectedStatements map[string]map[core.BuildStatement]bool
 }
 
 // ToDir exports a set of targets to the given directory.
 // It dies on any errors.
 func ToDir(state *core.BuildState, dir string, noTrim bool, targets []core.BuildLabel) {
 	e := &export{
-		state:            state,
-		noTrim:           noTrim,
-		targetDir:        dir,
-		exportedPackages: map[string]bool{},
-		exportedTargets:  map[core.BuildLabel]bool{},
+		state:              state,
+		noTrim:             noTrim,
+		targetDir:          dir,
+		exportedPackages:   map[string]bool{},
+		exportedTargets:    map[core.BuildLabel]bool{},
+		selectedStatements: map[string]map[core.BuildStatement]bool{},
 	}
 
 	if err := os.MkdirAll(dir, fs.DirPermissions); err != nil {
@@ -47,14 +49,12 @@ func ToDir(state *core.BuildState, dir string, noTrim bool, targets []core.Build
 			e.export(state.Graph.TargetOrDie(includeLabel))
 		}
 	}
+
 	for _, target := range targets {
 		e.export(state.Graph.TargetOrDie(target))
 	}
-	// Now write all the build files
-	packages := map[*core.Package]bool{}
-	for target := range e.exportedTargets {
-		packages[state.Graph.PackageOrDie(target)] = true
-	}
+
+	e.writeBuildStatements()
 
 	// Write any preloaded build defs as well; preloaded subincludes should be fine though.
 	for _, preload := range state.Config.Parse.PreloadBuildDefs {
@@ -62,33 +62,6 @@ func ToDir(state *core.BuildState, dir string, noTrim bool, targets []core.Build
 			log.Fatalf("Failed to copy preloaded build def %s: %s", preload, err)
 		}
 	}
-
-	if noTrim {
-		return // We have already exported the whole directory
-	}
-
-	for pkg := range packages {
-		if pkg.Name == parse.InternalPackageName {
-			continue // This isn't a real package to be copied
-		}
-		if pkg.Subrepo != nil {
-			continue // Don't copy subrepo BUILD files... they don't exist in our source tree
-		}
-		dest := filepath.Join(dir, pkg.Filename)
-		if err := fs.CopyFile(pkg.Filename, dest, 0); err != nil {
-			log.Fatalf("Failed to copy BUILD file %s: %s\n", pkg.Filename, err)
-		}
-		// Now rewrite the unused targets out of it
-		var victims []string
-		for _, target := range pkg.AllTargets() {
-			if !e.exportedTargets[target.Label] && !target.HasParent() {
-				victims = append(victims, target.Label.Name)
-			}
-		}
-		if err := gc.RewriteFile(state, dest, victims); err != nil {
-			log.Fatalf("Failed to rewrite BUILD file: %s\n", err)
-		}
-	}
 }
 
 func (e *export) exportPlzConf() {
@@ -99,7 +72,7 @@ func (e *export) exportPlzConf() {
 	for _, file := range profiles {
 		path := filepath.Join(e.targetDir, file)
 		if err := os.RemoveAll(path); err != nil {
-			log.Fatalf("failed to copy .plzconfig file %s: %v", file, err)
+			log.Fatalf("failed to remove .plzconfig file %s: %v", file, err)
 		}
 		if err := fs.CopyFile(file, path, 0); err != nil {
 			log.Fatalf("failed to copy .plzconfig file %s: %v", file, err)
@@ -129,8 +102,8 @@ var ignoreDirectories = map[string]bool{
 	".hg":     true,
 }
 
-// exportPackage exports the package BUILD file containing the given target and all sources
-func (e *export) exportPackage(target *core.BuildTarget) {
+// exportEntirePackage exports the package BUILD file containing the given target and all sources
+func (e *export) exportEntirePackage(target *core.BuildTarget) {
 	pkgName := target.Label.PackageName
 	if pkgName == parse.InternalPackageName {
 		return
@@ -169,34 +142,116 @@ func (e *export) exportPackage(target *core.BuildTarget) {
 	}
 }
 
+// selectBuildStatements exports BUILD statements that generate the build target.
+func (e *export) selectBuildStatements(target *core.BuildTarget) {
+	if target.Label.PackageName == parse.InternalPackageName {
+		return
+	}
+
+	log.Infof("Selecting Build stmts of %s with callstack:\n", target.Label.String())
+	for _, frame := range target.ParseMetadata.CallStack {
+		log.Infof("\t%v", frame)
+		if frame.Statement.Start == 0 && frame.Statement.End == 0 {
+			continue
+		}
+
+		if frame.Filename != "" {
+			if _, ok := e.selectedStatements[frame.Filename]; !ok {
+				e.selectedStatements[frame.Filename] = map[core.BuildStatement]bool{}
+			}
+			e.selectedStatements[frame.Filename][frame.Statement] = true
+		}
+		if frame.Filename == "" {
+			log.Warning("Package without filename %v", frame)
+		}
+	}
+}
+
 // export implements the logic of ToDir, but prevents repeating targets.
 func (e *export) export(target *core.BuildTarget) {
 	if e.exportedTargets[target.Label] {
 		return
 	}
+	log.Warningf("Exporting %v.\n", target.Label)
+	e.exportedTargets[target.Label] = true
+
 	// We want to export the package that made this subrepo available, but we still need to walk the target deps
 	// as it may depend on other subrepos or first party targets
 	if target.Subrepo != nil {
 		e.export(target.Subrepo.Target)
 	} else if e.noTrim {
 		// Export the whole package, rather than trying to trim the package down to only the targets we need
-		e.exportPackage(target)
+		e.exportEntirePackage(target)
 	} else {
+		e.selectBuildStatements(target)
 		e.exportSources(target)
 	}
 
-	e.exportedTargets[target.Label] = true
 	for _, dep := range target.Dependencies() {
 		e.export(dep)
 	}
 	for _, subinclude := range e.state.Graph.PackageOrDie(target.Label).AllSubincludes(e.state.Graph) {
 		e.export(e.state.Graph.TargetOrDie(subinclude))
 	}
+	// TODO handle parents from Callstack. How? Using the current label?
 	if parent := target.Parent(e.state.Graph); parent != nil && parent != target {
 		e.export(parent)
 	}
 }
 
+// writeBuildStatements writes the BUILD file statements to the export directory.
+func (e *export) writeBuildStatements() {
+	log.Infof("Selected Statements: %v", e.selectedStatements)
+
+	for filename, stmtMap := range e.selectedStatements {
+		stmts := make([]core.BuildStatement, 0, len(stmtMap))
+		for stmt := range stmtMap {
+			stmts = append(stmts, stmt)
+		}
+		// Sort statements by position to keep them in order
+		slices.SortFunc(stmts, func(a, b core.BuildStatement) int {
+			return int(a.Start)
+		})
+
+		e.writeBuildStatement(filename, stmts)
+	}
+}
+
+func (e *export) writeBuildStatement(filename string, stmts []core.BuildStatement) {
+	log.Infof("Writing file: %s", filename)
+	if err := fs.EnsureDir(filepath.Join(e.targetDir, filename)); err != nil {
+		log.Fatalf("failed to create directory for %s: %v", filename, err)
+	}
+	fw, err := os.Create(filepath.Join(e.targetDir, filename))
+	if err != nil {
+		log.Fatalf("failed to create BUILD file %s: %v", filename, err)
+	}
+	defer fw.Close()
+
+	fr, err := os.Open(filename)
+	if err != nil {
+		// TODO ensure only visiting correct files and move Warn to Fatal
+		log.Warningf("failed to open file %s: %v", filename, err)
+		return
+	}
+	defer fr.Close()
+
+	for _, s := range stmts {
+		buff := make([]byte, s.Len())
+		_, err := fr.ReadAt(buff, int64(s.Start))
+		if err != nil {
+			log.Fatalf("failed to read BUILD file %s: %v", filename, err)
+		}
+
+		if _, err := fw.Write(buff); err != nil {
+			log.Fatalf("failed to write statement to %s: %v", filename, err)
+		}
+		if _, err := fw.WriteString("\n\n"); err != nil {
+			log.Fatalf("failed to write newline to %s: %v", filename, err)
+		}
+	}
+}
+
 // Outputs exports the outputs of a target.
 func Outputs(state *core.BuildState, dir string, targets []core.BuildLabel) {
 	for _, label := range targets {

From f750c3960879da8e5ccfc3d18750cfc004d10a92 Mon Sep 17 00:00:00 2001
From: duarte <duarte@thoughtmachine.net>
Date: Wed, 18 Mar 2026 18:07:58 +0000
Subject: [PATCH 3/7] crude implementation of related targets and push call for
 native code

---
 src/core/build_target.go     | 20 +++++++++++++++++++-
 src/export/export.go         | 30 +++++++++++++++++-------------
 src/parse/asp/interpreter.go | 23 ++++++++++++++++++-----
 src/parse/asp/objects.go     |  3 ---
 src/parse/asp/targets.go     |  2 +-
 5 files changed, 55 insertions(+), 23 deletions(-)

diff --git a/src/core/build_target.go b/src/core/build_target.go
index eb9fe69a8..14f844ce8 100644
--- a/src/core/build_target.go
+++ b/src/core/build_target.go
@@ -322,7 +322,6 @@ func (cs *CallStack) Pop() CallFrame {
 type CallFrame struct {
 	MethodName string
 	Filename   string
-	Position   int
 	Label      BuildLabel
 	Statement  BuildStatement
 }
@@ -2013,6 +2012,25 @@ func (target *BuildTarget) NeedCoverage(state *BuildState) bool {
 	return state.NeedCoverage && !target.Test.NoOutput && !target.Test.NoCoverage && !target.HasAnyLabel(state.Config.Test.DisableCoverage)
 }
 
+// RelatedTargets returns all the targets in the package that originate from the same Build Statement.
+func (target *BuildTarget) RelatedTargets(graph *BuildGraph) BuildTargets {
+	relatedTargets := make(BuildTargets, 0)
+	pkg := graph.PackageOrDie(target.Label)
+	for _, otherTarget := range pkg.AllTargets() {
+		if otherTarget.isRelated(target) {
+			relatedTargets = append(relatedTargets, otherTarget)
+		}
+	}
+	return relatedTargets
+}
+
+func (target *BuildTarget) isRelated(other *BuildTarget) bool {
+	if len(target.ParseMetadata.CallStack) == 0 || len(target.ParseMetadata.CallStack) == 0 {
+		return false
+	}
+	return target.ParseMetadata.CallStack[0].Statement == other.ParseMetadata.CallStack[0].Statement
+}
+
 // Parent finds the parent of a build target, or nil if the target is parentless.
 // Note that this is a fairly informal relationship; we identify it by labels with the convention of
 // a leading _ and trailing hashtag on child rules, rather than storing pointers between them in the graph.
diff --git a/src/export/export.go b/src/export/export.go
index 77984ddca..9e8880ba2 100644
--- a/src/export/export.go
+++ b/src/export/export.go
@@ -4,10 +4,12 @@
 package export
 
 import (
+	"fmt"
 	iofs "io/fs"
 	"os"
 	"path/filepath"
 	"slices"
+	"strings"
 
 	"github.com/thought-machine/please/src/cli/logging"
 	"github.com/thought-machine/please/src/core"
@@ -50,6 +52,7 @@ func ToDir(state *core.BuildState, dir string, noTrim bool, targets []core.Build
 		}
 	}
 
+	log.Warningf("Exporting selected targets: %v", targets)
 	for _, target := range targets {
 		e.export(state.Graph.TargetOrDie(target))
 	}
@@ -89,6 +92,7 @@ func (e *export) exportSources(target *core.BuildTarget) {
 					if err := fs.RecursiveCopy(p, filepath.Join(e.targetDir, p), 0); err != nil {
 						log.Fatalf("Error copying file: %s\n", err)
 					}
+					log.Warning("Writing source file: %s", p)
 				}
 			}
 		}
@@ -151,11 +155,8 @@ func (e *export) selectBuildStatements(target *core.BuildTarget) {
 	log.Infof("Selecting Build stmts of %s with callstack:\n", target.Label.String())
 	for _, frame := range target.ParseMetadata.CallStack {
 		log.Infof("\t%v", frame)
-		if frame.Statement.Start == 0 && frame.Statement.End == 0 {
-			continue
-		}
 
-		if frame.Filename != "" {
+		if frame.Filename != "" && !strings.HasPrefix(frame.Filename, core.OutDir) {
 			if _, ok := e.selectedStatements[frame.Filename]; !ok {
 				e.selectedStatements[frame.Filename] = map[core.BuildStatement]bool{}
 			}
@@ -178,6 +179,7 @@ func (e *export) export(target *core.BuildTarget) {
 	// We want to export the package that made this subrepo available, but we still need to walk the target deps
 	// as it may depend on other subrepos or first party targets
 	if target.Subrepo != nil {
+		log.Warningf("Subrepo: %v", target.Subrepo.Target)
 		e.export(target.Subrepo.Target)
 	} else if e.noTrim {
 		// Export the whole package, rather than trying to trim the package down to only the targets we need
@@ -187,21 +189,23 @@ func (e *export) export(target *core.BuildTarget) {
 		e.exportSources(target)
 	}
 
+
 	for _, dep := range target.Dependencies() {
 		e.export(dep)
 	}
 	for _, subinclude := range e.state.Graph.PackageOrDie(target.Label).AllSubincludes(e.state.Graph) {
 		e.export(e.state.Graph.TargetOrDie(subinclude))
 	}
-	// TODO handle parents from Callstack. How? Using the current label?
-	if parent := target.Parent(e.state.Graph); parent != nil && parent != target {
-		e.export(parent)
+
+	for _, otherTarget := range target.RelatedTargets(e.state.Graph) {
+		log.Warningf("Exporting Other %s", otherTarget)
+		e.export(otherTarget)
 	}
 }
 
 // writeBuildStatements writes the BUILD file statements to the export directory.
 func (e *export) writeBuildStatements() {
-	log.Infof("Selected Statements: %v", e.selectedStatements)
+	log.Warningf("Selected Statements: %v", e.selectedStatements)
 
 	for filename, stmtMap := range e.selectedStatements {
 		stmts := make([]core.BuildStatement, 0, len(stmtMap))
@@ -210,15 +214,15 @@ func (e *export) writeBuildStatements() {
 		}
 		// Sort statements by position to keep them in order
 		slices.SortFunc(stmts, func(a, b core.BuildStatement) int {
-			return int(a.Start)
+			return a.Start - b.Start
 		})
 
-		e.writeBuildStatement(filename, stmts)
+		e.writeBuildFile(filename, stmts)
 	}
 }
 
-func (e *export) writeBuildStatement(filename string, stmts []core.BuildStatement) {
-	log.Infof("Writing file: %s", filename)
+func (e *export) writeBuildFile(filename string, stmts []core.BuildStatement) {
+	log.Warningf("Writing file: %s", filename)
 	if err := fs.EnsureDir(filepath.Join(e.targetDir, filename)); err != nil {
 		log.Fatalf("failed to create directory for %s: %v", filename, err)
 	}
@@ -246,7 +250,7 @@ func (e *export) writeBuildStatement(filename string, stmts []core.BuildStatemen
 		if _, err := fw.Write(buff); err != nil {
 			log.Fatalf("failed to write statement to %s: %v", filename, err)
 		}
-		if _, err := fw.WriteString("\n\n"); err != nil {
+		if _, err := fmt.Fprintf(fw, "\n#%+v\n\n", s); err != nil {
 			log.Fatalf("failed to write newline to %s: %v", filename, err)
 		}
 	}
diff --git a/src/parse/asp/interpreter.go b/src/parse/asp/interpreter.go
index 9cd8c31ac..9da4a414e 100644
--- a/src/parse/asp/interpreter.go
+++ b/src/parse/asp/interpreter.go
@@ -190,6 +190,8 @@ func (i *interpreter) interpretAll(pkg *core.Package, forLabel, dependent *core.
 		}
 	}
 
+	log.Warning("Preload done for Package: %s", pkg.Label())
+
 	s.Set("CONFIG", s.config)
 	_, err := i.interpretStatements(s, statements)
 	if err == nil {
@@ -520,7 +522,11 @@ func (s *scope) LoadSingletons(state *core.BuildState) {
 	}
 }
 
-func (s *scope) PushCall(name string) {
+func (s *scope) PushCall(f *pyFunc) bool {
+	if s.cursor == nil {
+		return false	// skip builtin method calls (e.g. format)
+	}
+
 	stmt := core.BuildStatement{
 		Start: int(s.cursor.Pos),
 		End: int(s.cursor.EndPos),
@@ -530,16 +536,17 @@ func (s *scope) PushCall(name string) {
 		label = s.parsingFor.label
 	}
 
-	s.interpreter.callStack.Push(core.CallFrame{MethodName: name, Filename: s.filename, Label: label, Statement: stmt})
-
+	log.Debug("PushCall ", f.name, s.filename,label, stmt, s.cursor)
 
+	s.interpreter.callStack.Push(core.CallFrame{MethodName: f.name, Filename: s.filename, Label: label, Statement: stmt})
+	return true
 }
 
 func (s *scope) PopCall() {
 	s.interpreter.callStack.Pop()
 }
 
-func (s *scope) CallStackSnapshot() core.CallStack {
+func (s *scope) CallStackSnapshot(name string) core.CallStack {
 	snapshot := make(core.CallStack, len(s.interpreter.callStack))
 	copy(snapshot, s.interpreter.callStack)
 
@@ -547,7 +554,7 @@ func (s *scope) CallStackSnapshot() core.CallStack {
 	for _,v := range s.interpreter.callStack {
 		stack += fmt.Sprintf("\n\t%v", v)
 	}
-	log.Info("CallStack Snapshot: %s", stack)
+	log.Warningf("CallStack Snapshot for %s: %s", name, stack)
 
 	return snapshot
 }
@@ -564,6 +571,7 @@ func (s *scope) interpretStatements(statements []*Statement) pyObject {
 	}()
 	for _, stmt = range statements {
 		s.cursor = stmt
+		// log.Warningf("Cursor val (%s/%s): %v", s.filename, s.parsingFor, s.cursor)
 		if stmt.FuncDef != nil {
 			s.Set(stmt.FuncDef.Name, newPyFunc(s, stmt.FuncDef))
 		} else if stmt.If != nil {
@@ -1084,6 +1092,11 @@ func (s *scope) callObject(name string, obj pyObject, c *Call) pyObject {
 	if !ok {
 		s.Error("Non-callable object '%s' (is a %s)", name, obj.Type())
 	}
+
+	if ok := s.PushCall(f); ok {
+		defer s.PopCall()
+	}
+
 	return f.Call(s, c)
 }
 
diff --git a/src/parse/asp/objects.go b/src/parse/asp/objects.go
index 420cb3e21..7adea0b7c 100644
--- a/src/parse/asp/objects.go
+++ b/src/parse/asp/objects.go
@@ -699,9 +699,6 @@ func (f *pyFunc) Call(s *scope, c *Call) pyObject {
 		return f.callNative(s, c)
 	}
 
-	s.PushCall(f.name)
-	defer s.PopCall()
-
 	s2 := f.scope.newScope(s.pkg, s.mode, f.scope.filename, len(f.args)+1)
 	s2.config = s.config
 	s2.Set("CONFIG", s.config) // This needs to be copied across too :(
diff --git a/src/parse/asp/targets.go b/src/parse/asp/targets.go
index 9fe057150..8fa23c818 100644
--- a/src/parse/asp/targets.go
+++ b/src/parse/asp/targets.go
@@ -102,7 +102,7 @@ func createTarget(s *scope, args []pyObject) *core.BuildTarget {
 	label.Subrepo = s.pkg.SubrepoName
 
 	target := core.NewBuildTarget(label)
-	target.ParseMetadata.CallStack = s.CallStackSnapshot()
+	target.ParseMetadata.CallStack = s.CallStackSnapshot(name)
 	target.Subrepo = s.pkg.Subrepo
 	target.IsBinary = isTruthy(binaryBuildRuleArgIdx)
 	target.IsSubrepo = isTruthy(subrepoArgIdx)

From 048b19e070954ec3266b3d3b8f522be90c16b5e4 Mon Sep 17 00:00:00 2001
From: duarte <duarte@thoughtmachine.net>
Date: Wed, 18 Mar 2026 18:59:36 +0000
Subject: [PATCH 4/7] filename as part of build statement

---
 src/core/build_target.go     |  4 ++--
 src/export/export.go         | 10 +++++-----
 src/parse/asp/interpreter.go |  7 ++++---
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/src/core/build_target.go b/src/core/build_target.go
index 14f844ce8..5d866c5d7 100644
--- a/src/core/build_target.go
+++ b/src/core/build_target.go
@@ -321,12 +321,12 @@ func (cs *CallStack) Pop() CallFrame {
 
 type CallFrame struct {
 	MethodName string
-	Filename   string
 	Label      BuildLabel
 	Statement  BuildStatement
 }
 
 type BuildStatement struct {
+	Filename   string
 	Start int
 	End int
 }
@@ -2025,7 +2025,7 @@ func (target *BuildTarget) RelatedTargets(graph *BuildGraph) BuildTargets {
 }
 
 func (target *BuildTarget) isRelated(other *BuildTarget) bool {
-	if len(target.ParseMetadata.CallStack) == 0 || len(target.ParseMetadata.CallStack) == 0 {
+	if len(target.ParseMetadata.CallStack) == 0 || len(other.ParseMetadata.CallStack) == 0 {
 		return false
 	}
 	return target.ParseMetadata.CallStack[0].Statement == other.ParseMetadata.CallStack[0].Statement
diff --git a/src/export/export.go b/src/export/export.go
index 9e8880ba2..f7424d05e 100644
--- a/src/export/export.go
+++ b/src/export/export.go
@@ -156,13 +156,13 @@ func (e *export) selectBuildStatements(target *core.BuildTarget) {
 	for _, frame := range target.ParseMetadata.CallStack {
 		log.Infof("\t%v", frame)
 
-		if frame.Filename != "" && !strings.HasPrefix(frame.Filename, core.OutDir) {
-			if _, ok := e.selectedStatements[frame.Filename]; !ok {
-				e.selectedStatements[frame.Filename] = map[core.BuildStatement]bool{}
+		if frame.Statement.Filename != "" && !strings.HasPrefix(frame.Statement.Filename, core.OutDir) {
+			if _, ok := e.selectedStatements[frame.Statement.Filename]; !ok {
+				e.selectedStatements[frame.Statement.Filename] = map[core.BuildStatement]bool{}
 			}
-			e.selectedStatements[frame.Filename][frame.Statement] = true
+			e.selectedStatements[frame.Statement.Filename][frame.Statement] = true
 		}
-		if frame.Filename == "" {
+		if frame.Statement.Filename == "" {
 			log.Warning("Package without filename %v", frame)
 		}
 	}
diff --git a/src/parse/asp/interpreter.go b/src/parse/asp/interpreter.go
index 9da4a414e..7bc91f406 100644
--- a/src/parse/asp/interpreter.go
+++ b/src/parse/asp/interpreter.go
@@ -528,8 +528,9 @@ func (s *scope) PushCall(f *pyFunc) bool {
 	}
 
 	stmt := core.BuildStatement{
-		Start: int(s.cursor.Pos),
-		End: int(s.cursor.EndPos),
+		Filename: s.filename,
+		Start:    int(s.cursor.Pos),
+		End:      int(s.cursor.EndPos),
 	}
 	var label core.BuildLabel
 	if s.parsingFor != nil {
@@ -538,7 +539,7 @@ func (s *scope) PushCall(f *pyFunc) bool {
 
 	log.Debug("PushCall ", f.name, s.filename,label, stmt, s.cursor)
 
-	s.interpreter.callStack.Push(core.CallFrame{MethodName: f.name, Filename: s.filename, Label: label, Statement: stmt})
+	s.interpreter.callStack.Push(core.CallFrame{MethodName: f.name, Label: label, Statement: stmt})
 	return true
 }
 

From 0bb9ef5465408a985613aacded27535d6e37e13c Mon Sep 17 00:00:00 2001
From: duarte <duarte@thoughtmachine.net>
Date: Thu, 19 Mar 2026 12:20:22 +0000
Subject: [PATCH 5/7] test: initial build statement testing

---
 test/build_defs/test.build_defs             |  3 +-
 test/export/BUILD                           | 16 ++++++++++
 test/export/repo/test/BUILD_FILE            |  8 +++++
 test/export/repo/test/file.txt              |  1 +
 test/export/test_build_statement_content.sh | 33 +++++++++++++++++++++
 5 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 test/export/repo/test/BUILD_FILE
 create mode 100644 test/export/repo/test/file.txt
 create mode 100755 test/export/test_build_statement_content.sh

diff --git a/test/build_defs/test.build_defs b/test/build_defs/test.build_defs
index 5830e3f62..33ab98369 100644
--- a/test/build_defs/test.build_defs
+++ b/test/build_defs/test.build_defs
@@ -10,6 +10,7 @@ def please_repo_e2e_test(
         expected_output: dict = {},
         expect_output_contains: dict = {},
         expect_output_doesnt_contain: dict = {},
+        tool_content_checker = ["//test/build_defs:content_checker"],
         labels: list = [],
 ):
     plz_command = plz_command.replace("plz ", "$TOOLS_PLEASE ")
@@ -37,7 +38,7 @@ def please_repo_e2e_test(
     data["BASE_CONFIG"] = ["//test/build_defs:base_config"]
 
     tools["PLEASE"] = ["//package:installed_files|please"]
-    tools["CONTENT_CHECKER"] = ["//test/build_defs:content_checker"]
+    tools["CONTENT_CHECKER"] = tool_content_checker
 
     return gentest(
         name = name,
diff --git a/test/export/BUILD b/test/export/BUILD
index c0f7ed5a0..9ac48b353 100644
--- a/test/export/BUILD
+++ b/test/export/BUILD
@@ -4,3 +4,19 @@ plz_e2e_test(
     name = "export_src_please_test",
     cmd = "plz export --output plz-out/plzexport //src/core && plz --repo_root=$(plz query reporoot)/plz-out/plzexport build //src/core",
 )
+
+sh_binary(
+    name = "build_statement_checker",
+    main = "test_build_statement_content.sh",
+)
+
+# Export a target generated by a native genrule target.
+please_repo_e2e_test(
+    name = "export_native_genrule_bstmt",
+    plz_command = "plz export --output plz-out/plzexport //test:native_genrule",
+    expected_output = {
+        "plz-out/plzexport/test/BUILD_FILE": "test/BUILD_FILE:native_genrule",
+    },
+    tool_content_checker = [":build_statement_checker"],
+    repo = "repo",
+)
diff --git a/test/export/repo/test/BUILD_FILE b/test/export/repo/test/BUILD_FILE
new file mode 100644
index 000000000..e57512d48
--- /dev/null
+++ b/test/export/repo/test/BUILD_FILE
@@ -0,0 +1,8 @@
+# Start BStmt native_genrule
+genrule(
+    name = "native_genrule",
+    srcs = ["file.txt"],
+    outs = ["file.wordcount"],
+    cmd = "wc $SRCS > $OUT",
+)
+# End BStmt
diff --git a/test/export/repo/test/file.txt b/test/export/repo/test/file.txt
new file mode 100644
index 000000000..9768ee14c
--- /dev/null
+++ b/test/export/repo/test/file.txt
@@ -0,0 +1 @@
+Test source file
diff --git a/test/export/test_build_statement_content.sh b/test/export/test_build_statement_content.sh
new file mode 100755
index 000000000..939638cab
--- /dev/null
+++ b/test/export/test_build_statement_content.sh
@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+
+
+gen_file=$1
+if ! test -f "$gen_file"; then
+  echo "$gen_file" doesnt exist
+  exit 1
+fi
+
+# Statement identifier of type path/file:name
+stmt_identifier=$2
+# string BEFORE the last colon
+file_path="${stmt_identifier%:*}"
+# string AFTER the last colon
+statement_name="${stmt_identifier##*:}"
+
+if ! test -f "$file_path"; then
+  echo "$file_path" doesnt exist
+  exit 1
+fi
+
+# Extract the block into a variable
+ORIG_CONTENT=$(sed -n "/# Start BStmt ${statement_name}/,/# End BStmt/{ /# /d; p; }" "$file_path")
+
+if ! grep -Fq "$ORIG_CONTENT" "$gen_file"; then
+  printf '%s\n%s\n%s\n%s\n%s\n' \
+    "${gen_file} doesnt contain" \
+    "${ORIG_CONTENT}" \
+    "---- it contains ----" \
+    "$(cat "$gen_file")" \
+    "---- EOF ----"
+  exit 1
+fi

From c4a305a34f9f4c8c09eb3d91d084b0868b08477f Mon Sep 17 00:00:00 2001
From: duarte <duarte@thoughtmachine.net>
Date: Thu, 19 Mar 2026 17:11:51 +0000
Subject: [PATCH 6/7] test: move to export_e2e build rule

---
 test/build_defs/test.build_defs             |  7 ++-
 test/export/BUILD                           | 48 +++++++++++++++------
 test/export/repo/test/BUILD_FILE            |  4 +-
 test/export/test_build_statement_content.sh | 20 ++++-----
 4 files changed, 52 insertions(+), 27 deletions(-)

diff --git a/test/build_defs/test.build_defs b/test/build_defs/test.build_defs
index 33ab98369..c7b5df9bb 100644
--- a/test/build_defs/test.build_defs
+++ b/test/build_defs/test.build_defs
@@ -5,12 +5,13 @@ def please_repo_e2e_test(
         repo: str,
         data: dict={},
         deps: list=[],
+        defer_cmd=[],
         tools: dict={},
+        tool_content_checker = ["//test/build_defs:content_checker"],
         expected_failure: bool = False,
         expected_output: dict = {},
         expect_output_contains: dict = {},
         expect_output_doesnt_contain: dict = {},
-        tool_content_checker = ["//test/build_defs:content_checker"],
         labels: list = [],
 ):
     plz_command = plz_command.replace("plz ", "$TOOLS_PLEASE ")
@@ -32,6 +33,10 @@ def please_repo_e2e_test(
     if expect_output_doesnt_contain:
         test_cmd += [f'_STR="$(cat {o})" _SUBSTR="{c}" && if [ -z "${_STR##*$_SUBSTR*}" ]; then echo "$_STR"; exit 1; fi' for o, c in expect_output_doesnt_contain.items()]
 
+    # defer commands should be added last
+    if defer_cmd:
+        test_cmd += [cmd.replace("plz ", "$TOOLS_PLEASE ") for cmd in defer_cmd]
+
     test_cmd = ' && '.join(test_cmd)
 
     data["REPO"] = [repo]
diff --git a/test/export/BUILD b/test/export/BUILD
index 9ac48b353..bf483516b 100644
--- a/test/export/BUILD
+++ b/test/export/BUILD
@@ -1,22 +1,46 @@
 subinclude("//test/build_defs")
 
-plz_e2e_test(
-    name = "export_src_please_test",
-    cmd = "plz export --output plz-out/plzexport //src/core && plz --repo_root=$(plz query reporoot)/plz-out/plzexport build //src/core",
-)
-
 sh_binary(
     name = "build_statement_checker",
     main = "test_build_statement_content.sh",
 )
 
+# Runs an export e2e test. It purposely tests for different aspect (e.g. BUILD files, sources)
+# within the same test to avoid the overhead of exporting multiple times.
+def please_export_e2e_test(
+        name:str,
+        export_target:str,
+        repo:str):
+
+    EXPORT_DIR = "plz-out/plzexport"
+    please_target = "//" + export_target
+    file_path, target_name = export_target.split(":")
+    build_file = file_path + "/BUILD_FILE"
+
+    return please_repo_e2e_test(
+        name = name,
+        repo = repo,
+        plz_command = f"plz export --output {EXPORT_DIR} {please_target}",
+        defer_cmd = [
+            # Tests the contents of the exported BUILD file
+            f'$TOOLS_BUILD_STATEMENT_CHECKER "{EXPORT_DIR}/{build_file}" "{build_file}" "{target_name}"',
+            # Tests building the exported target
+            f'plz build --repo_root=$(plz query reporoot)/plz-out/plzexport "{please_target}"',
+        ],
+        tools = {
+            "BUILD_STATEMENT_CHECKER": "//test/export:build_statement_checker"
+        },
+    )
+
+# Generic catch-all test on internal repo.
+plz_e2e_test(
+    name = "export_src_please_test",
+    cmd = "plz export --output plz-out/plzexport //src/core && plz --repo_root=$(plz query reporoot)/plz-out/plzexport build //src/core",
+)
+
 # Export a target generated by a native genrule target.
-please_repo_e2e_test(
-    name = "export_native_genrule_bstmt",
-    plz_command = "plz export --output plz-out/plzexport //test:native_genrule",
-    expected_output = {
-        "plz-out/plzexport/test/BUILD_FILE": "test/BUILD_FILE:native_genrule",
-    },
-    tool_content_checker = [":build_statement_checker"],
+please_export_e2e_test(
+    name = "export_native_genrule",
+    export_target = "test:native_genrule",
     repo = "repo",
 )
diff --git a/test/export/repo/test/BUILD_FILE b/test/export/repo/test/BUILD_FILE
index e57512d48..e198e11f9 100644
--- a/test/export/repo/test/BUILD_FILE
+++ b/test/export/repo/test/BUILD_FILE
@@ -1,8 +1,8 @@
-# Start BStmt native_genrule
+# Start BUILDStmt native_genrule
 genrule(
     name = "native_genrule",
     srcs = ["file.txt"],
     outs = ["file.wordcount"],
     cmd = "wc $SRCS > $OUT",
 )
-# End BStmt
+# End BUILDStmt
diff --git a/test/export/test_build_statement_content.sh b/test/export/test_build_statement_content.sh
index 939638cab..92d4a054b 100755
--- a/test/export/test_build_statement_content.sh
+++ b/test/export/test_build_statement_content.sh
@@ -1,29 +1,25 @@
 #!/usr/bin/env bash
 
-
 gen_file=$1
+orig_file=$2
+stmt_identifier=$3
+
 if ! test -f "$gen_file"; then
   echo "$gen_file" doesnt exist
   exit 1
 fi
 
-# Statement identifier of type path/file:name
-stmt_identifier=$2
-# string BEFORE the last colon
-file_path="${stmt_identifier%:*}"
-# string AFTER the last colon
-statement_name="${stmt_identifier##*:}"
-
-if ! test -f "$file_path"; then
-  echo "$file_path" doesnt exist
+if ! test -f "$orig_file"; then
+  echo "$orig_file" doesnt exist
   exit 1
 fi
 
 # Extract the block into a variable
-ORIG_CONTENT=$(sed -n "/# Start BStmt ${statement_name}/,/# End BStmt/{ /# /d; p; }" "$file_path")
+ORIG_CONTENT=$(sed -n "/# Start BStmt ${stmt_identifier}/,/# End BStmt/{ /# /d; p; }" "$orig_file")
 
 if ! grep -Fq "$ORIG_CONTENT" "$gen_file"; then
-  printf '%s\n%s\n%s\n%s\n%s\n' \
+  printf '%s\n%s\n%s\n%s\n%s\n%s\n' \
+    "BUILD statements mismatch" \
     "${gen_file} doesnt contain" \
     "${ORIG_CONTENT}" \
     "---- it contains ----" \

From 5383e64b4cec824dc8d387e736578e915b072fc0 Mon Sep 17 00:00:00 2001
From: duarte <duarte@thoughtmachine.net>
Date: Fri, 20 Mar 2026 15:50:27 +0000
Subject: [PATCH 7/7] test: add test for custom build def and rework build stmt
 checked

build stmt checker now uses awk, supports more than one stmt associated with with a target and has a strict matching mode
---
 test/export/BUILD                             |  27 ++--
 test/export/build_statement_checker.sh        | 119 ++++++++++++++++++
 test/export/repo/.plzconfig                   |   0
 test/export/repo/test/BUILD_FILE              |   8 --
 test/export/repo/test_builtins/BUILD_FILE     |  17 +++
 .../repo/{test => test_builtins}/file.txt     |   0
 test/export/repo/test_custom_defs/BUILD_FILE  |  11 ++
 .../test_custom_defs/build_defs/BUILD_FILE    |   5 +
 .../build_defs/custom.build_defs              |  10 ++
 test/export/repo/test_custom_defs/file.txt    |   1 +
 test/export/test_build_statement_content.sh   |  29 -----
 11 files changed, 183 insertions(+), 44 deletions(-)
 create mode 100755 test/export/build_statement_checker.sh
 create mode 100644 test/export/repo/.plzconfig
 delete mode 100644 test/export/repo/test/BUILD_FILE
 create mode 100644 test/export/repo/test_builtins/BUILD_FILE
 rename test/export/repo/{test => test_builtins}/file.txt (100%)
 create mode 100644 test/export/repo/test_custom_defs/BUILD_FILE
 create mode 100644 test/export/repo/test_custom_defs/build_defs/BUILD_FILE
 create mode 100644 test/export/repo/test_custom_defs/build_defs/custom.build_defs
 create mode 100644 test/export/repo/test_custom_defs/file.txt
 delete mode 100755 test/export/test_build_statement_content.sh

diff --git a/test/export/BUILD b/test/export/BUILD
index bf483516b..b47719a48 100644
--- a/test/export/BUILD
+++ b/test/export/BUILD
@@ -2,7 +2,7 @@ subinclude("//test/build_defs")
 
 sh_binary(
     name = "build_statement_checker",
-    main = "test_build_statement_content.sh",
+    main = "build_statement_checker.sh",
 )
 
 # Runs an export e2e test. It purposely tests for different aspect (e.g. BUILD files, sources)
@@ -10,22 +10,27 @@ sh_binary(
 def please_export_e2e_test(
         name:str,
         export_target:str,
-        repo:str):
+        repo:str,
+        strict_check_build_stmt:bool = False,
+    ):
 
     EXPORT_DIR = "plz-out/plzexport"
+
     please_target = "//" + export_target
     file_path, target_name = export_target.split(":")
     build_file = file_path + "/BUILD_FILE"
 
+    strict_opt = "--strict" if strict_check_build_stmt else ""
+
     return please_repo_e2e_test(
         name = name,
         repo = repo,
         plz_command = f"plz export --output {EXPORT_DIR} {please_target}",
         defer_cmd = [
             # Tests the contents of the exported BUILD file
-            f'$TOOLS_BUILD_STATEMENT_CHECKER "{EXPORT_DIR}/{build_file}" "{build_file}" "{target_name}"',
-            # Tests building the exported target
-            f'plz build --repo_root=$(plz query reporoot)/plz-out/plzexport "{please_target}"',
+            f'$TOOLS_BUILD_STATEMENT_CHECKER {strict_opt} --exported "{EXPORT_DIR}/{build_file}" --original "{build_file}" --target "{target_name}"',
+            # Tests building the exported target which in turn ensures the sources are included
+            f'plz build --repo_root=$(plz query reporoot)/{EXPORT_DIR} "{please_target}"',
         ],
         tools = {
             "BUILD_STATEMENT_CHECKER": "//test/export:build_statement_checker"
@@ -38,9 +43,17 @@ plz_e2e_test(
     cmd = "plz export --output plz-out/plzexport //src/core && plz --repo_root=$(plz query reporoot)/plz-out/plzexport build //src/core",
 )
 
-# Export a target generated by a native genrule target.
+# Export a target generated by a native genrule target and trim unused build statements.
 please_export_e2e_test(
     name = "export_native_genrule",
-    export_target = "test:native_genrule",
+    export_target = "test_builtins:native_genrule",
+    repo = "repo",
+    strict_check_build_stmt = True,
+)
+
+# Export a target generated by a custom build def.
+please_export_e2e_test(
+    name = "export_custom_target",
+    export_target = "test_custom_defs:custom_target",
     repo = "repo",
 )
diff --git a/test/export/build_statement_checker.sh b/test/export/build_statement_checker.sh
new file mode 100755
index 000000000..f8bcb9c91
--- /dev/null
+++ b/test/export/build_statement_checker.sh
@@ -0,0 +1,119 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+strict_match=false
+exported_file=""
+original_file=""
+target_name=""
+
+while [[ "$#" -gt 0 ]]; do
+  case $1 in
+    --strict)
+      strict_match=true
+      shift
+      ;;
+    --exported)
+      exported_file=$2
+      shift 2
+      ;;
+    --original)
+      original_file=$2
+      shift 2
+      ;;
+    --target)
+      target_name=$2
+      shift 2
+      ;;
+    -*)
+      echo "Unknown option: $1" >&2
+      exit 1
+      ;;
+    *)
+      echo "Unknown argument: $1" >&2
+      exit 1
+      ;;
+  esac
+done
+
+if [[ -z "$exported_file" ]] || [[ -z "$original_file" ]] || [[ -z "$target_name" ]]; then
+  echo "Usage: $0 [--strict] --exported <file> --original <file> --target <name>" >&2
+  exit 1
+fi
+
+if [[ ! -f "$exported_file" ]]; then
+  echo "$exported_file doesnt exist" >&2
+  exit 1
+fi
+
+if [[ ! -f "$original_file" ]]; then
+  echo "$original_file doesnt exist" >&2
+  exit 1
+fi
+
+readonly START_DELIM="# BUILD_STMT_START"
+readonly END_DELIM="# BUILD_STMT_END"
+
+# Using awk to extract statement blocks directly into an array.
+blocks=()
+while IFS= read -r -d '' block; do
+  blocks+=("$block")
+done < <(awk -v id="$target_name" -v start_delim="$START_DELIM" -v end_delim="$END_DELIM" '
+  BEGIN { in_block = 0; block = "" }
+  $0 == start_delim " " id {
+    in_block = 1;
+    block = "";
+    next;
+  }
+  $0 == end_delim {
+    if (in_block) {
+      in_block = 0;
+      printf "%s\0", block;
+    }
+    next;
+  }
+  in_block {
+    block = block ? block "\n" $0 : $0
+  }
+' "$original_file")
+
+if [[ ${#blocks[@]} -eq 0 ]]; then
+  echo "Failed to pull original content for $target_name" >&2
+  exit 1
+fi
+
+# Ensure that ALL required blocks are present in the generated file
+for block_content in "${blocks[@]}"; do
+  if ! grep -Fq "$block_content" "$exported_file"; then
+    printf '%s\n%s\n%s\n%s\n%s\n%s\n' \
+      "BUILD statements mismatch" \
+      "${exported_file} doesnt contain" \
+      "${block_content}" \
+      "---- it contains ----" \
+      "$(cat "$exported_file")" \
+      "---- EOF ----" >&2
+    exit 1
+  fi
+done
+
+# If --strict is enabled, ensure ONLY these blocks are present
+# (ignoring all whitespace, newlines and comments).
+if [[ "$strict_match" == true ]]; then
+  concatenated_blocks=""
+  for block_content in "${blocks[@]}"; do
+    concatenated_blocks="${concatenated_blocks}${block_content}"
+  done
+
+  stripped_blocks=$(echo -n "$concatenated_blocks" | sed 's/#.*//' | tr -d ' \t\n\r')
+  stripped_exported_file=$(sed 's/#.*//' "$exported_file" | tr -d ' \t\n\r')
+
+  if [[ "$stripped_blocks" != "$stripped_exported_file" ]]; then
+    printf '%s\n' "Strict match failed: exported file contains extra or out-of-order content." >&2
+    printf '%s\n' "---- Expected (stripped) ----" >&2
+    printf '%s\n' "$stripped_blocks" >&2
+    printf '%s\n' "---- Got (stripped) ----" >&2
+    printf '%s\n' "$stripped_exported_file" >&2
+    exit 1
+  fi
+fi
+
+exit 0
diff --git a/test/export/repo/.plzconfig b/test/export/repo/.plzconfig
new file mode 100644
index 000000000..e69de29bb
diff --git a/test/export/repo/test/BUILD_FILE b/test/export/repo/test/BUILD_FILE
deleted file mode 100644
index e198e11f9..000000000
--- a/test/export/repo/test/BUILD_FILE
+++ /dev/null
@@ -1,8 +0,0 @@
-# Start BUILDStmt native_genrule
-genrule(
-    name = "native_genrule",
-    srcs = ["file.txt"],
-    outs = ["file.wordcount"],
-    cmd = "wc $SRCS > $OUT",
-)
-# End BUILDStmt
diff --git a/test/export/repo/test_builtins/BUILD_FILE b/test/export/repo/test_builtins/BUILD_FILE
new file mode 100644
index 000000000..c533d280d
--- /dev/null
+++ b/test/export/repo/test_builtins/BUILD_FILE
@@ -0,0 +1,17 @@
+# BUILD_STMT_START native_genrule
+genrule(
+    name = "native_genrule",
+    srcs = ["file.txt"],
+    outs = ["file.wordcount"],
+    cmd = "wc $SRCS > $OUT",
+)
+# BUILD_STMT_END
+
+
+# Du mmy target to be trimmed
+genrule(
+    name = "dummy",
+    srcs = ["file.txt"],
+    outs = ["dummy"],
+    cmd = "cat $SRCS > $OUT",
+)
diff --git a/test/export/repo/test/file.txt b/test/export/repo/test_builtins/file.txt
similarity index 100%
rename from test/export/repo/test/file.txt
rename to test/export/repo/test_builtins/file.txt
diff --git a/test/export/repo/test_custom_defs/BUILD_FILE b/test/export/repo/test_custom_defs/BUILD_FILE
new file mode 100644
index 000000000..df8819489
--- /dev/null
+++ b/test/export/repo/test_custom_defs/BUILD_FILE
@@ -0,0 +1,11 @@
+# BUILD_STMT_START custom_target
+subinclude("//test_custom_defs/build_defs")
+# BUILD_STMT_END
+
+# BUILD_STMT_START custom_target
+simple_custom_target(
+    name = "custom_target",
+    srcs = ["file.txt"],
+    outs = ["file.out"],
+)
+# BUILD_STMT_END
diff --git a/test/export/repo/test_custom_defs/build_defs/BUILD_FILE b/test/export/repo/test_custom_defs/build_defs/BUILD_FILE
new file mode 100644
index 000000000..cf7d4a898
--- /dev/null
+++ b/test/export/repo/test_custom_defs/build_defs/BUILD_FILE
@@ -0,0 +1,5 @@
+filegroup(
+    name = "build_defs",
+    srcs = ["custom.build_defs"],
+    visibility = ["//test_custom_defs/..."],
+)
diff --git a/test/export/repo/test_custom_defs/build_defs/custom.build_defs b/test/export/repo/test_custom_defs/build_defs/custom.build_defs
new file mode 100644
index 000000000..8fe3a6021
--- /dev/null
+++ b/test/export/repo/test_custom_defs/build_defs/custom.build_defs
@@ -0,0 +1,10 @@
+def simple_custom_target(
+        name:str,
+        srcs:list=[],
+        outs:list=[]):
+    return genrule(
+        name = name,
+        srcs = srcs,
+        outs = outs,
+        cmd = "cat $SRCS > $OUT",
+    )
diff --git a/test/export/repo/test_custom_defs/file.txt b/test/export/repo/test_custom_defs/file.txt
new file mode 100644
index 000000000..9768ee14c
--- /dev/null
+++ b/test/export/repo/test_custom_defs/file.txt
@@ -0,0 +1 @@
+Test source file
diff --git a/test/export/test_build_statement_content.sh b/test/export/test_build_statement_content.sh
deleted file mode 100755
index 92d4a054b..000000000
--- a/test/export/test_build_statement_content.sh
+++ /dev/null
@@ -1,29 +0,0 @@
-#!/usr/bin/env bash
-
-gen_file=$1
-orig_file=$2
-stmt_identifier=$3
-
-if ! test -f "$gen_file"; then
-  echo "$gen_file" doesnt exist
-  exit 1
-fi
-
-if ! test -f "$orig_file"; then
-  echo "$orig_file" doesnt exist
-  exit 1
-fi
-
-# Extract the block into a variable
-ORIG_CONTENT=$(sed -n "/# Start BStmt ${stmt_identifier}/,/# End BStmt/{ /# /d; p; }" "$orig_file")
-
-if ! grep -Fq "$ORIG_CONTENT" "$gen_file"; then
-  printf '%s\n%s\n%s\n%s\n%s\n%s\n' \
-    "BUILD statements mismatch" \
-    "${gen_file} doesnt contain" \
-    "${ORIG_CONTENT}" \
-    "---- it contains ----" \
-    "$(cat "$gen_file")" \
-    "---- EOF ----"
-  exit 1
-fi