fix #1184: implicit "**/" in "sideEffects"

CHANGELOG.md

@@ -24,6 +24,10 @@
 
     However, doing this is very un-ergonomic and exporting something as an arbitrary name is impossible outside of `export * from`. So this proposal is designed to fully fill out the possibility matrix and make arbitrary alias names a proper first-class feature.
 
+* Implement more accurate `sideEffects` behavior from Webpack ([#1184](https://github.com/evanw/esbuild/issues/1184))
+
+    This release adds support for the implicit `**/` prefix that must be added to paths in the `sideEffects` array in `package.json` if the path does not contain `/`. Another way of saying this is if `package.json` contains a `sideEffects` array with a string that doesn't contain a `/` then it should be treated as a file name instead of a path. Previously esbuild treated all strings in this array as paths, which does not match how Webpack behaves. The result of this meant that esbuild could consider files to have no side effects while Webpack would consider the same files to have side effects. This bug should now be fixed.
+
 ## 0.11.13
 
 * Implement ergonomic brand checks for private fields

internal/resolver/package_json.go

@@ -260,8 +260,13 @@ func (r resolverQuery) parsePackageJSON(inputPath string) *packageJSON {
 					continue
 				}
 
-				absPattern := r.fs.Join(inputPath, js_lexer.UTF16ToString(item.Value))
-				re, hadWildcard := globToEscapedRegexp(absPattern)
+				// Reference: https://github.com/webpack/webpack/blob/ed175cd22f89eb9fecd0a70572a3fd0be028e77c/lib/optimize/SideEffectsFlagPlugin.js
+				pattern := js_lexer.UTF16ToString(item.Value)
+				if !strings.ContainsRune(pattern, '/') {
+					pattern = "**/" + pattern
+				}
+				absPattern := r.fs.Join(inputPath, pattern)
+				re, hadWildcard := globstarToEscapedRegexp(absPattern)
 
 				// Wildcard patterns require more expensive matching
 				if hadWildcard {
@@ -290,27 +295,59 @@ func (r resolverQuery) parsePackageJSON(inputPath string) *packageJSON {
 	return packageJSON
 }
 
-func globToEscapedRegexp(glob string) (string, bool) {
+// Reference: https://github.com/fitzgen/glob-to-regexp/blob/2abf65a834259c6504ed3b80e85f893f8cd99127/index.js
+func globstarToEscapedRegexp(glob string) (string, bool) {
 	sb := strings.Builder{}
 	sb.WriteByte('^')
 	hadWildcard := false
+	n := len(glob)
 
-	for _, c := range glob {
+	for i := 0; i < n; i++ {
+		c := glob[i]
 		switch c {
 		case '\\', '^', '$', '.', '+', '|', '(', ')', '[', ']', '{', '}':
 			sb.WriteByte('\\')
-			sb.WriteRune(c)
-
-		case '*':
-			sb.WriteString(".*")
-			hadWildcard = true
+			sb.WriteByte(c)
 
 		case '?':
 			sb.WriteByte('.')
 			hadWildcard = true
 
+		case '*':
+			// Move over all consecutive "*"'s.
+			// Also store the previous and next characters
+			prevChar := -1
+			if i > 0 {
+				prevChar = int(glob[i-1])
+			}
+			starCount := 1
+			for i+1 < n && glob[i+1] == '*' {
+				starCount++
+				i++
+			}
+			nextChar := -1
+			if i+1 < n {
+				nextChar = int(glob[i+1])
+			}
+
+			// Determine if this is a globstar segment
+			isGlobstar := starCount > 1 && // multiple "*"'s
+				(prevChar == '/' || prevChar == -1) && // from the start of the segment
+				(nextChar == '/' || nextChar == -1) // to the end of the segment
+
+			if isGlobstar {
+				// It's a globstar, so match zero or more path segments
+				sb.WriteString("(?:[^/]*(?:/|$))*")
+				i++ // Move over the "/"
+			} else {
+				// It's not a globstar, so only match one path segment
+				sb.WriteString("[^/]*")
+			}
+
+			hadWildcard = true
+
 		default:
-			sb.WriteRune(c)
+			sb.WriteByte(c)
 		}
 	}
 

scripts/end-to-end-tests.js

@@ -2349,6 +2349,18 @@
       'entry.js': `import {foo, bar} from './foo'; let unused = foo; if (bar) throw 'expected "foo" to be tree-shaken'`,
       'foo.js': `module.exports = {get foo() { module.exports.bar = 1 }, bar: 0}`,
     }),
+
+    // Test for an implicit and explicit "**/" prefix (see https://github.com/evanw/esbuild/issues/1184)
+    test(['--bundle', 'entry.js', '--outfile=node.js'], {
+      'entry.js': `import './foo'; if (global.dce6 !== 123) throw 'fail'`,
+      'foo/dir/x.js': `global.dce6 = 123`,
+      'foo/package.json': `{ "main": "dir/x", "sideEffects": ["x.*"] }`,
+    }),
+    test(['--bundle', 'entry.js', '--outfile=node.js'], {
+      'entry.js': `import './foo'; if (global.dce6 !== 123) throw 'fail'`,
+      'foo/dir/x.js': `global.dce6 = 123`,
+      'foo/package.json': `{ "main": "dir/x", "sideEffects": ["**/x.*"] }`,
+    }),
   )
 
   // Test obscure CommonJS symbol edge cases