fix #766: support recursive symlinks in resolver

CHANGELOG.md

@@ -36,6 +36,10 @@
 
     It would be a change in semantics to minify this code to either `--some-var:;` or `var(--some-var,)` due to the whitespace significance of CSS variables, so such transformations are invalid. With this release, esbuild should now preserve whitespace in these two situations (CSS variable declarations and CSS variable references).
 
+* Add support for recursive symlinks during path resolution ([#766](https://github.com/evanw/esbuild/issues/766))
+
+    Previously recursive symlinks (a symlink that points to another symlink) were an unhandled case in the path resolution algorithm. Now these cases should be supported up to a depth of 256 symlinks. This means esbuild's path resolution should now work with multi-level `yarn link` scenarios.
+
 ## 0.8.42
 
 * Fix crash with block-level function declaration and `--keep-names` ([#755](https://github.com/evanw/esbuild/issues/755))

internal/fs/fs_real.go

@@ -310,23 +310,32 @@ func (fs *realFS) kind(dir string, base string) (symlink string, kind EntryKind)
 
 	// Follow symlinks now so the cache contains the translation
 	if (mode & os.ModeSymlink) != 0 {
-		link, err := os.Readlink(entryPath)
-		if err != nil {
-			return // Skip over this entry
-		}
-		if !fs.fp.isAbs(link) {
-			link = fs.fp.join([]string{dir, link})
-		}
-		symlink = fs.fp.clean(link)
+		symlink = entryPath
+		linksWalked := 0
+		for {
+			linksWalked++
+			if linksWalked > 255 {
+				return // Error: too many links
+			}
+			link, err := os.Readlink(symlink)
+			if err != nil {
+				return // Skip over this entry
+			}
+			if !fs.fp.isAbs(link) {
+				link = fs.fp.join([]string{dir, link})
+			}
+			symlink = fs.fp.clean(link)
 
-		// Re-run "lstat" on the symlink target
-		stat2, err2 := os.Lstat(symlink)
-		if err2 != nil {
-			return // Skip over this entry
-		}
-		mode = stat2.Mode()
-		if (mode & os.ModeSymlink) != 0 {
-			return // Symlink chains are not supported
+			// Re-run "lstat" on the symlink target
+			stat2, err2 := os.Lstat(symlink)
+			if err2 != nil {
+				return // Skip over this entry
+			}
+			mode = stat2.Mode()
+			if (mode & os.ModeSymlink) == 0 {
+				break
+			}
+			dir = fs.fp.dir(symlink)
 		}
 	}
 

scripts/end-to-end-tests.js

@@ -109,6 +109,25 @@
         `,
         'c': { symlink: `a/b` },
       }, { cwd: 'c' }),
+
+      // This is a test for https://github.com/evanw/esbuild/issues/766
+      test(['--bundle', 'impl/index.mjs', '--outfile=node.js', '--format=cjs'], {
+        'config/yarn/link/@monorepo-source/a': { symlink: `../../../../monorepo-source/packages/a` },
+        'config/yarn/link/@monorepo-source/b': { symlink: `../../../../monorepo-source/packages/b` },
+        'impl/node_modules/@monorepo-source/b': { symlink: `../../../config/yarn/link/@monorepo-source/b` },
+        'impl/index.mjs': `
+          import { fn } from '@monorepo-source/b';
+          if (fn() !== 123) throw 'fail';
+        `,
+        'monorepo-source/packages/a/index.mjs': `
+          export function foo() { return 123; }
+        `,
+        'monorepo-source/packages/b/node_modules/@monorepo-source/a': { symlink: `../../../../../config/yarn/link/@monorepo-source/a` },
+        'monorepo-source/packages/b/index.mjs': `
+          import { foo } from '@monorepo-source/a';
+          export function fn() { return foo(); }
+        `,
+      }),
     )
   }