Summary

Rework error stack traces to produce cleaner, more informative output using the existing Java stack trace mechanism (no custom call stack). This is an alternative to #633 that avoids the performance regression by resolving names at parse time and filtering frames during formatting rather than maintaining a separate call stack.

Key changes

• Named frames from AST: callTargetName extracts function names from Apply AST nodes at the expression level ([foo], [std.assertEqual], [anonymous]), replacing opaque node type names like [Apply0], [Apply3].

• Frame filtering: Only Apply* and ApplyBuiltin* expression frames are kept in stack traces, filtering out intermediate AST node types that add noise.

• Root frame: Every stack trace now includes a [<root>] outermost frame pointing to the top-level expression, injected by Interpreter.evaluateImpl.

• Builtin error collapsing: When an error originates from inside a builtin's Scala code (e.g., type checking, missing arguments), the builtin name is collapsed into the error message as a prefix rather than shown as a separate frame:

  • sjsonnet.Error: [std.manifestTomlEx] Wrong parameter type: expected Object, got array
  • sjsonnet.Error: [foo] Too many args, has 2 parameter(s)

• Same-position collapsing: Adjacent frames at the same file position are collapsed to avoid redundant lines.

• Caused-by chain: formatError now includes Caused by: output for wrapped exceptions (e.g., native function panics).

• Removed redundant prefixes: "Function " prefix removed from error messages since the frame name now provides that context.

Example outputs

Builtin error (collapsed into message):

sjsonnet.Error: [std.assertEqual] assertEqual failed: {"x":1} != {"x":2}
    at [<root>].(assert_equal4.jsonnet:1:16)

Function parameter error (collapsed):

sjsonnet.Error: [anonymous] parameter x not bound in call
    at [<root>].(bad_function_call.jsonnet:1:16)

Error inside function body (full trace):

sjsonnet.Error: xxx
    at [foo].(error_in_method.jsonnet:1:23)
    at [<root>].(error_in_method.jsonnet:1:7)

Native function panic (with caused-by):

sjsonnet.Error: [std.nativePanic] Internal Error
    at [<root>].(native_panic.jsonnet:1:26)
Caused by: java.lang.RuntimeException: native function panic

Test plan

• All JVM tests pass (140/140)
• Golden files regenerated for test_suite, go_test_suite, new_test_suite (340 files)
• Unit test expectations updated (EvaluatorTests, StdFlatMapTests, StdWithKeyFTests, Std0150FunctionsTests)
• Native/extvar golden files manually verified (require special test harness args)
• JS BaseFileTests updated for new format