Write to a temp file if there are diffs and output instructions for how to compare

Author: micahhahn

src/Elm/Kernel/Test.js

@@ -20,6 +20,7 @@ function _Test_runThunk(thunk)
 
 const fs = require('node:fs');
 const path = require('node:path');
+const os = require('node:os');
 
 function _Test_readFile(filePath)
 {
@@ -51,18 +52,17 @@ function _Test_readFile(filePath)
     }
 }
 
-var _Test_writeFile = F2(function(filePath, contents)
+function WriteFile(root, filePath, contents)
 {
     // Test for this early as `resolve` will strip training slashes
     if (filePath.slice(-1) == path.sep) {
         return __Result_Err(__File_IsDirectory);
     }
 
-    // Protect against writing files above the "tests" directory
-    const testsPath = path.resolve("tests");
-    const fullPath = path.resolve(testsPath, filePath);
+    // Protect against writing files above the root directory
+    const fullPath = path.resolve(root, filePath);
 
-    if (!fullPath.startsWith(testsPath))
+    if (!fullPath.startsWith(root))
     {
         return __Result_Err(__File_PathEscapesDirectory);
     }
@@ -74,10 +74,24 @@ var _Test_writeFile = F2(function(filePath, contents)
 
     try {
         fs.writeFileSync(fullPath, contents);
-        return __Result_Ok(__Utils_Tuple0);
+        return __Result_Ok(fullPath);
     }
     catch (err)
     {   
         return __Result_Err(__File_GeneralFileError(err.toString()));
     }
+}
+
+var _Test_writeFile = F2(function(filePath, contents)
+{
+    return WriteFile(path.resolve("tests"), filePath, contents);
+})
+
+var tempDir = null;
+var _Test_writeTempFile = F2(function(filePath, contents)
+{
+    if (tempDir === null)
+        tempDir = os.tmpdir();
+
+    return WriteFile(tempDir, filePath, contents);
 })

src/Expect.elm

@@ -3,7 +3,8 @@ module Expect exposing
     , lessThan, atMost, greaterThan, atLeast
     , FloatingPointTolerance(..), within, notWithin
     , ok, err, equalLists, equalDicts, equalSets
-    , pass, fail, onFail, equalToFile
+    , equalToFile
+    , pass, fail, onFail
     )
 
 {-| A library to create `Expectation`s, which describe a claim to be tested.
@@ -42,10 +43,12 @@ or both. For an in-depth look, see our [Guide to Floating Point Comparison](#gui
 
 @docs ok, err, equalLists, equalDicts, equalSets
 
+
 ## Golden Files
 
 @docs equalToFile
 
+
 ## Customizing
 
 These functions will let you build your own expectations.
@@ -106,8 +109,8 @@ Another example is comparing values that are on either side of zero. `0.0001` is
 -}
 
 import Dict exposing (Dict)
-import Set exposing (Set)
 import File
+import Set exposing (Set)
 import Test.Distribution
 import Test.Expectation
 import Test.Internal as Internal
@@ -580,7 +583,7 @@ equalSets expected actual =
         reportCollectionFailure "Expect.equalSets" expected actual missingKeys extraKeys
 
 
-{-| Tests the a String is equal to the contents of the file stored at the file path. 
+{-| Tests the a String is equal to the contents of the file stored at the file path.
 
 If the file does not exist, it will be created and this test will pass.
 
@@ -591,30 +594,53 @@ All file paths are scoped to be within the "tests/" directory.
 -}
 equalToFile : String -> String -> Expectation
 equalToFile filePath actual =
-    case File.readFile filePath of 
+    case File.readFile filePath of
         Err File.FileNotFound ->
-            case File.writeFile filePath actual of 
-                Err (File.GeneralFileError fileError) -> 
+            case File.writeFile filePath actual of
+                Err (File.GeneralFileError fileError) ->
                     Test.Expectation.fail { description = "Expect.equalToFile encountered a general file error: " ++ fileError, reason = Custom }
 
                 -- This case should be impossible non general file errors should have been surfaced in the call to `readFile` above.
-                Err _ -> 
-                    Test.Expectation.fail { description = "Expect.equalToFile encountered an unexpected error", reason = Custom  }
+                Err _ ->
+                    Test.Expectation.fail { description = "Expect.equalToFile encountered an unexpected error", reason = Custom }
 
                 Ok _ ->
                     pass
 
-        Err File.IsDirectory -> 
+        Err File.IsDirectory ->
             Test.Expectation.fail { description = "Expect.equalToFile was given a directory instead of a file", reason = Custom }
 
-        Err File.PathEscapesDirectory -> 
+        Err File.PathEscapesDirectory ->
             Test.Expectation.fail { description = "Expect.equalToFile was given a path that would escape the tests/ directory", reason = Custom }
 
-        Err (File.GeneralFileError fileError) -> 
+        Err (File.GeneralFileError fileError) ->
             Test.Expectation.fail { description = "Expect.equalToFile encountered a general file error: " ++ fileError, reason = Custom }
 
-        Ok contents -> 
-            equateWith ("equalToFile \'" ++ filePath ++ "\'") (==) contents actual
+        Ok ( existingAbsolutePath, contents ) ->
+            if actual == contents then
+                pass
+
+            else
+                case File.writeTempFile filePath actual of
+                    Ok newAbsolutePath ->
+                        let
+                            message =
+                                [ "The contents of " ++ filePath ++ "changed!"
+                                , "To compare run: git diff --no-index " ++ existingAbsolutePath ++ " " ++ newAbsolutePath
+                                ]
+
+                            messageWithVisualDiff =
+                                if String.endsWith ".html" filePath then
+                                    message ++ [ "To visually compare run: open file://" ++ existingAbsolutePath ++ " file://" ++ newAbsolutePath ]
+
+                                else
+                                    message
+                        in
+                        Test.Expectation.fail { description = String.join "\n\n" messageWithVisualDiff, reason = Custom }
+
+                    _ ->
+                        Test.Expectation.fail { description = "Expect.equalToFile encountered an unexpected error", reason = Custom }
+
 
 {-| Always passes.
 

src/File.elm

@@ -1,15 +1,45 @@
-module File exposing (readFile, writeFile, FileError(..))
+module File exposing (AbsolutePath, FileError(..), RelativePath, readFile, writeFile, writeTempFile)
 
 import Elm.Kernel.Test
 
+
 type FileError
     = FileNotFound
     | IsDirectory
     | PathEscapesDirectory
     | GeneralFileError String
 
-readFile : String -> Result FileError String
-readFile = Elm.Kernel.Test.readFile
 
-writeFile : String -> String -> Result FileError ()
-writeFile = Elm.Kernel.Test.writeFile
+type alias RelativePath =
+    String
+
+
+type alias AbsolutePath =
+    String
+
+
+{-| Read the contents of the filePath relative to "tests/"
+-}
+readFile : RelativePath -> Result FileError ( AbsolutePath, String )
+readFile =
+    Elm.Kernel.Test.readFile
+
+
+{-| Write the contents of the second argument to the file path in the first argument relative to "tests/"
+
+Returns the absolute file path if successful.
+
+-}
+writeFile : RelativePath -> String -> Result FileError AbsolutePath
+writeFile =
+    Elm.Kernel.Test.writeFile
+
+
+{-| Write the contents of the second argument to the file path in the first argument relative to a temp directory
+
+Returns the absolute file path if successful.
+
+-}
+writeTempFile : RelativePath -> String -> Result FileError AbsolutePath
+writeTempFile =
+    Elm.Kernel.Test.writeTempFile