fix #2730: alias now strips a trailing slash

CHANGELOG.md

@@ -26,6 +26,10 @@
      }
     ```
 
+* The alias feature now strips a trailing slash ([#2730](https://github.com/evanw/esbuild/issues/2730))
+
+    People sometimes add a trailing slash to the name of one of node's built-in modules to force node to import from the file system instead of importing the built-in module. For example, importing `util` imports node's built-in module called `util` but importing `util/` tries to find a package called `util` on the file system. Previously attempting to use esbuild's package alias feature to replace imports to `util` with a specific file would fail because the file path would also gain a trailing slash (e.g. mapping `util` to `./file.js` turned `util/` into `./file.js/`). With this release, esbuild will now omit the path suffix if it's a single trailing slash, which should now allow you to successfully apply aliases to these import paths.
+
 ## 0.16.6
 
 * Do not mark subpath imports as external with `--packages=external` ([#2741](https://github.com/evanw/esbuild/issues/2741))

internal/bundler/bundler.go

@@ -548,7 +548,7 @@ func ResolveFailureErrorTextSuggestionNotes(
 	}
 	hint := ""
 
-	if resolver.IsPackagePath(path) {
+	if resolver.IsPackagePath(path) && !fs.IsAbs(path) {
 		hint = fmt.Sprintf("You can mark the path %q as external to exclude it from the bundle, which will remove this error.", path)
 		if kind == ast.ImportRequire {
 			hint += " You can also surround this \"require\" call with a try/catch block to handle this failure at run-time instead of bundle-time."

internal/bundler/bundler_default_test.go

@@ -6924,6 +6924,7 @@ func TestPackageAlias(t *testing.T) {
 				import "@abs-path/pkg6"
 				import "@abs-path/pkg7/foo"
 				import "@scope-only/pkg8"
+				import "slash/"
 			`,
 			"/nested3/index.js":                     `import "pkg3"`,
 			"/nested3/node_modules/alias3/index.js": `test failure`,
@@ -6935,6 +6936,7 @@ func TestPackageAlias(t *testing.T) {
 			"/alias6/dir/index.js":                  `console.log(6)`,
 			"/alias7/dir/foo/index.js":              `console.log(7)`,
 			"/alias8/dir/pkg8/index.js":             `console.log(8)`,
+			"/alias9/some/file.js":                  `console.log(9)`,
 		},
 		entryPaths: []string{"/entry.js"},
 		options: config.Options{
@@ -6949,6 +6951,7 @@ func TestPackageAlias(t *testing.T) {
 				"@abs-path/pkg6": `/alias6/dir`,
 				"@abs-path/pkg7": `/alias7/dir`,
 				"@scope-only":    "/alias8/dir",
+				"slash":          "/alias9/some/file.js",
 			},
 		},
 	})

internal/bundler/snapshots/snapshots_loader.txt

@@ -1528,6 +1528,9 @@ console.log(7);
 // alias8/dir/pkg8/index.js
 console.log(8);
 
+// alias9/some/file.js
+console.log(9);
+
 ================================================================================
 TestRequireCustomExtensionBase64
 ---------- /out.js ----------

internal/resolver/resolver.go

@@ -313,7 +313,21 @@ func (rr *resolver) Resolve(sourceDir string, importPath string, kind ast.Import
 				// when using Yarn PnP because Yarn PnP doesn't allow nested packages
 				// to "reach outside" of their normal dependency lists.
 				sourceDir = r.fs.Cwd()
-				debugMeta.ModifiedImportPath = value + importPath[len(key):]
+				if tail := importPath[len(key):]; tail != "/" {
+					// Don't include the trailing characters if they are equal to a
+					// single slash. This comes up because you can abuse this quirk of
+					// node's path resolution to force node to load the package from the
+					// file system instead of as a built-in module. For example, "util"
+					// is node's built-in module while "util/" is one on the file system.
+					// Leaving the trailing slash in place causes problems for people:
+					// https://github.com/evanw/esbuild/issues/2730. It should be ok to
+					// always strip the trailing slash even when using the alias feature
+					// to swap one package for another (except when you swap a reference
+					// to one built-in node module with another but really why would you
+					// do that).
+					value += tail
+				}
+				debugMeta.ModifiedImportPath = value
 				if r.debugLogs != nil {
 					r.debugLogs.addNote(fmt.Sprintf("  Matched with alias from %q to %q", key, value))
 					r.debugLogs.addNote(fmt.Sprintf("  Modified import path from %q to %q", importPath, debugMeta.ModifiedImportPath))