fix #4144: node path resolution edge case

Author: evanw

CHANGELOG.md

@@ -48,6 +48,10 @@
 
     This fix was contributed by [@mxschmitt](https://github.com/mxschmitt).
 
+* Fix path resolution edge case ([#4144](https://github.com/evanw/esbuild/issues/4144))
+
+    This fixes an edge case where esbuild's path resolution algorithm could deviate from node's path resolution algorithm. It involves a confusing situation where a directory shares the same file name as a file (but without the file extension). See the linked issue for specific details. This appears to be a case where esbuild is correctly following [node's published resolution algorithm](https://nodejs.org/api/modules.html#all-together) but where node itself is doing something different. Specifically the step `LOAD_AS_FILE` appears to be skipped when the input ends with `..`. This release changes esbuild's behavior for this edge case to match node's behavior.
+
 * Update Go from 1.23.7 to 1.23.8 ([#4133](https://github.com/evanw/esbuild/issues/4133), [#4134](https://github.com/evanw/esbuild/pull/4134))
 
     This should have no effect on existing code as this version change does not change Go's operating system support. It may remove certain reports from vulnerability scanners that detect which version of the Go compiler esbuild uses, such as for CVE-2025-22871.

internal/bundler_tests/bundler_packagejson_test.go

@@ -3035,3 +3035,37 @@ func TestPackageJsonExportsDefaultWarningIssue3887(t *testing.T) {
 		debugLogs: true,
 	})
 }
+
+// https://github.com/evanw/esbuild/issues/4144
+func TestConfusingNameCollisionsIssue4144(t *testing.T) {
+	packagejson_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				import { it } from 'mydependency'
+				console.log(it())
+			`,
+			"/node_modules/mydependency/package.json": `
+				{
+					"main": "./package/index.js"
+				}
+			`,
+			"/node_modules/mydependency/package/index.js": `
+				export { it } from './utils'
+				export let works = true
+			`,
+			"/node_modules/mydependency/package/utils/index.js": `
+				export { it } from './utils'
+			`,
+			"/node_modules/mydependency/package/utils/utils.js": `
+				// This should resolve to "../index.js" not "../../package.json"
+				import { works } from '..'
+				export function it() { return works }
+			`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.js",
+		},
+	})
+}

internal/bundler_tests/snapshots/snapshots_packagejson.txt

@@ -3,6 +3,20 @@ TestCommonJSVariableInESMTypeModule
 // entry.js
 module.exports = null;
 
+================================================================================
+TestConfusingNameCollisionsIssue4144
+---------- /out.js ----------
+// node_modules/mydependency/package/utils/utils.js
+function it() {
+  return works;
+}
+
+// node_modules/mydependency/package/index.js
+var works = true;
+
+// entry.js
+console.log(it());
+
 ================================================================================
 TestPackageJsonBadExportsDefaultWarningIssue3867
 ---------- /out.js ----------

internal/resolver/resolver.go

@@ -1000,27 +1000,48 @@ func (r resolverQuery) resolveWithoutSymlinks(sourceDir string, sourceDirInfo *d
 			return &ResolveResult{PathPair: PathPair{Primary: logger.Path{Text: absPath, Namespace: "file"}, IsExternal: true}}
 		}
 
-		// Check the "browser" map
-		if importDirInfo := r.dirInfoCached(r.fs.Dir(absPath)); importDirInfo != nil {
-			if remapped, ok := r.checkBrowserMap(importDirInfo, absPath, absolutePathKind); ok {
-				if remapped == nil {
-					return &ResolveResult{PathPair: PathPair{Primary: logger.Path{Text: absPath, Namespace: "file", Flags: logger.PathDisabled}}}
-				}
-				if remappedResult, ok, diffCase, sideEffects := r.resolveWithoutRemapping(importDirInfo.enclosingBrowserScope, *remapped); ok {
-					result = ResolveResult{PathPair: remappedResult, DifferentCase: diffCase, PrimarySideEffectsData: sideEffects}
-					checkRelative = false
-					checkPackage = false
-				}
-			}
-		}
-
-		if checkRelative {
-			if absolute, ok, diffCase := r.loadAsFileOrDirectory(absPath); ok {
+		// Node's actual behavior deviates from its published algorithm by not
+		// running the "LOAD_AS_FILE" step if the import path looks like it
+		// resolves to a directory instead of a file. Attempt to replicate that
+		// behavior here. This really only matters for intentionally confusing
+		// edge cases where a directory is named the same thing as a file.
+		// Unfortunately people actually create situations like this.
+		hasTrailingSlash := importPath == "." ||
+			importPath == ".." ||
+			strings.HasSuffix(importPath, "/") ||
+			strings.HasSuffix(importPath, "/.") ||
+			strings.HasSuffix(importPath, "/..")
+
+		if hasTrailingSlash {
+			if absolute, ok, diffCase := r.loadAsDirectory(absPath); ok {
 				checkPackage = false
 				result = ResolveResult{PathPair: absolute, DifferentCase: diffCase}
 			} else if !checkPackage {
 				return nil
 			}
+		} else {
+			// Check the "browser" map
+			if importDirInfo := r.dirInfoCached(r.fs.Dir(absPath)); importDirInfo != nil {
+				if remapped, ok := r.checkBrowserMap(importDirInfo, absPath, absolutePathKind); ok {
+					if remapped == nil {
+						return &ResolveResult{PathPair: PathPair{Primary: logger.Path{Text: absPath, Namespace: "file", Flags: logger.PathDisabled}}}
+					}
+					if remappedResult, ok, diffCase, sideEffects := r.resolveWithoutRemapping(importDirInfo.enclosingBrowserScope, *remapped); ok {
+						result = ResolveResult{PathPair: remappedResult, DifferentCase: diffCase, PrimarySideEffectsData: sideEffects}
+						checkRelative = false
+						checkPackage = false
+					}
+				}
+			}
+
+			if checkRelative {
+				if absolute, ok, diffCase := r.loadAsFileOrDirectory(absPath); ok {
+					checkPackage = false
+					result = ResolveResult{PathPair: absolute, DifferentCase: diffCase}
+				} else if !checkPackage {
+					return nil
+				}
+			}
 		}
 	}
 
@@ -1899,6 +1920,19 @@ func (r resolverQuery) loadAsFileOrDirectory(path string) (PathPair, bool, *fs.D
 		return PathPair{Primary: logger.Path{Text: absolute, Namespace: "file"}}, true, diffCase
 	}
 
+	return r.loadAsDirectory(path)
+}
+
+func (r resolverQuery) loadAsDirectory(path string) (PathPair, bool, *fs.DifferentCase) {
+	extensionOrder := r.options.ExtensionOrder
+	if r.kind.MustResolveToCSS() {
+		// Use a special import order for CSS "@import" imports
+		extensionOrder = r.cssExtensionOrder
+	} else if helpers.IsInsideNodeModules(path) {
+		// Use a special import order for imports inside "node_modules"
+		extensionOrder = r.nodeModulesExtensionOrder
+	}
+
 	// Is this a directory?
 	if r.debugLogs != nil {
 		r.debugLogs.addNote(fmt.Sprintf("Attempting to load %q as a directory", path))