fix #2322: a log message for ambiguous re-exports

CHANGELOG.md

@@ -1,5 +1,27 @@
 # Changelog
 
+## Unreleased
+
+* Add a log message for ambiguous re-exports ([#2322](https://github.com/evanw/esbuild/issues/2322))
+
+    In JavaScript, you can re-export symbols from another file using `export * from './another-file'`. When you do this from multiple files that export different symbols with the same name, this creates an ambiguous export which is causes that name to not be exported. This is harmless if you don't plan on using the ambiguous export name, so esbuild doesn't have a warning for this. But if you do want a warning for this (or if you want to make it an error), you can now opt-in to seeing this log message with `--log-override:ambiguous-import=warning` or `--log-override:ambiguous-import=error`. The log message looks like this:
+
+    ```
+    ▲ [WARNING] Re-export of "common" in "example.js" is ambiguous and has been removed [ambiguous-import]
+
+      One definition of "common" comes from "a.js" here:
+
+        a.js:2:11:
+          2 │ export let common = 2
+            ╵            ~~~~~~
+
+      Another definition of "common" comes from "b.js" here:
+
+        b.js:3:14:
+          3 │ export { b as common }
+            ╵               ~~~~~~
+    ```
+
 ## 0.14.44
 
 * Add a `copy` loader ([#2255](https://github.com/evanw/esbuild/issues/2255))

internal/bundler/bundler_default_test.go

@@ -6397,3 +6397,28 @@ ident.js: DEBUG: Indirect calls to "require" will not be bundled
 `,
 	})
 }
+
+func TestAmbiguousReexportMsg(t *testing.T) {
+	loader_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				export * from './a'
+				export * from './b'
+				export * from './c'
+			`,
+			"/a.js": `export let a = 1, x = 2`,
+			"/b.js": `export let b = 3; export { b as x }`,
+			"/c.js": `export let c = 4, x = 5`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:         config.ModeBundle,
+			AbsOutputDir: "/out",
+		},
+		debugLogs: true,
+		expectedCompileLog: `DEBUG: Re-export of "x" in "entry.js" is ambiguous and has been removed
+a.js: NOTE: One definition of "x" comes from "a.js" here:
+b.js: NOTE: Another definition of "x" comes from "b.js" here:
+`,
+	})
+}

internal/bundler/linker.go

@@ -1443,21 +1443,42 @@ func (c *linkerContext) scanImportsAndExports() {
 			aliases := make([]string, 0, len(repr.Meta.ResolvedExports))
 		nextAlias:
 			for alias, export := range repr.Meta.ResolvedExports {
+				otherFile := &c.graph.Files[export.SourceIndex].InputFile
+				otherRepr := otherFile.Repr.(*graph.JSRepr)
+
 				// Re-exporting multiple symbols with the same name causes an ambiguous
 				// export. These names cannot be used and should not end up in generated code.
-				otherRepr := c.graph.Files[export.SourceIndex].InputFile.Repr.(*graph.JSRepr)
 				if len(export.PotentiallyAmbiguousExportStarRefs) > 0 {
 					mainRef := export.Ref
+					mainLoc := export.NameLoc
 					if imported, ok := otherRepr.Meta.ImportsToBind[export.Ref]; ok {
 						mainRef = imported.Ref
+						mainLoc = imported.NameLoc
 					}
+
 					for _, ambiguousExport := range export.PotentiallyAmbiguousExportStarRefs {
-						ambiguousRepr := c.graph.Files[ambiguousExport.SourceIndex].InputFile.Repr.(*graph.JSRepr)
+						ambiguousFile := &c.graph.Files[ambiguousExport.SourceIndex].InputFile
+						ambiguousRepr := ambiguousFile.Repr.(*graph.JSRepr)
 						ambiguousRef := ambiguousExport.Ref
+						ambiguousLoc := ambiguousExport.NameLoc
 						if imported, ok := ambiguousRepr.Meta.ImportsToBind[ambiguousExport.Ref]; ok {
 							ambiguousRef = imported.Ref
+							ambiguousLoc = imported.NameLoc
 						}
+
 						if mainRef != ambiguousRef {
+							file := &c.graph.Files[sourceIndex].InputFile
+							otherTracker := logger.MakeLineColumnTracker(&otherFile.Source)
+							ambiguousTracker := logger.MakeLineColumnTracker(&ambiguousFile.Source)
+							c.log.AddIDWithNotes(logger.MsgID_Bundler_AmbiguousReexport, logger.Debug, nil, logger.Range{},
+								fmt.Sprintf("Re-export of %q in %q is ambiguous and has been removed", alias, file.Source.PrettyPath),
+								[]logger.MsgData{
+									otherTracker.MsgData(js_lexer.RangeOfIdentifier(otherFile.Source, mainLoc),
+										fmt.Sprintf("One definition of %q comes from %q here:", alias, otherFile.Source.PrettyPath)),
+									ambiguousTracker.MsgData(js_lexer.RangeOfIdentifier(ambiguousFile.Source, ambiguousLoc),
+										fmt.Sprintf("Another definition of %q comes from %q here:", alias, ambiguousFile.Source.PrettyPath)),
+								},
+							)
 							continue nextAlias
 						}
 					}

internal/bundler/snapshots/snapshots_loader.txt

@@ -1,3 +1,20 @@
+TestAmbiguousReexportMsg
+---------- /out/entry.js ----------
+// a.js
+var a = 1;
+
+// b.js
+var b = 3;
+
+// c.js
+var c = 4;
+export {
+  a,
+  b,
+  c
+};
+
+================================================================================
 TestAutoDetectMimeTypeFromExtension
 ---------- /out.js ----------
 // test.svg

internal/logger/msg_ids.go

@@ -49,6 +49,7 @@ const (
 	MsgID_CSS_UnsupportedCSSProperty
 
 	// Bundler
+	MsgID_Bundler_AmbiguousReexport
 	MsgID_Bundler_DifferentPathCase
 	MsgID_Bundler_IgnoredBareImport
 	MsgID_Bundler_IgnoredDynamicImport
@@ -156,6 +157,8 @@ func StringToMsgIDs(str string, logLevel LogLevel, overrides map[MsgID]LogLevel)
 		overrides[MsgID_CSS_UnsupportedCSSProperty] = logLevel
 
 	// Bundler
+	case "ambiguous-reexport":
+		overrides[MsgID_Bundler_AmbiguousReexport] = logLevel
 	case "different-path-case":
 		overrides[MsgID_Bundler_DifferentPathCase] = logLevel
 	case "ignored-bare-import":
@@ -266,6 +269,8 @@ func MsgIDToString(id MsgID) string {
 		return "unsupported-css-property"
 
 	// Bundler
+	case MsgID_Bundler_AmbiguousReexport:
+		return "ambiguous-reexport"
 	case MsgID_Bundler_DifferentPathCase:
 		return "different-path-case"
 	case MsgID_Bundler_IgnoredBareImport: