loader: support "all:" prefix in //go:embed patterns

  The "all:" prefix in //go:embed directives instructs the compiler to
  include hidden files (starting with "." or "_") when embedding a
  directory. Previously, the prefix was passed literally to path.Match,
  which would never match.

  This change parses the "all:" prefix once in parseGoEmbed and stores it
  in an embedPattern struct, which carries both the glob pattern and the
  includeHidden flag through validation and matching.

  Fixes embedding with patterns like "//go:embed all:static".

Author: abgoyal

loader/loader.go

@@ -549,7 +549,7 @@ func (p *Package) extractEmbedLines(addError func(error)) {
 					}
 
 					// Look for //go:embed comments.
-					var allPatterns []string
+					var allPatterns []embedPattern
 					for _, comment := range doc.List {
 						if comment.Text != "//go:embed" && !strings.HasPrefix(comment.Text, "//go:embed ") {
 							continue
@@ -577,20 +577,20 @@ func (p *Package) extractEmbedLines(addError func(error)) {
 							})
 							continue
 						}
-						for _, pattern := range patterns {
+						for _, ep := range patterns {
 							// Check that the pattern is well-formed.
 							// It must be valid: the Go toolchain has already
 							// checked for invalid patterns. But let's check
 							// anyway to be sure.
-							if _, err := path.Match(pattern, ""); err != nil {
+							if _, err := path.Match(ep.pattern, ""); err != nil {
 								addError(types.Error{
 									Fset: p.program.fset,
 									Pos:  comment.Pos(),
 									Msg:  "invalid pattern syntax",
 								})
 								continue
 							}
-							allPatterns = append(allPatterns, pattern)
+							allPatterns = append(allPatterns, ep)
 						}
 					}
 
@@ -624,16 +624,8 @@ func (p *Package) extractEmbedLines(addError func(error)) {
 						// Match all //go:embed patterns against the embed files
 						// provided by `go list`.
 						for _, name := range p.EmbedFiles {
-							for _, pattern := range allPatterns {
-								// Check for "all:" prefix which includes hidden files.
-								// See: https://pkg.go.dev/embed#hdr-Directives
-								includeHidden := false
-								matchPat := pattern
-								if strings.HasPrefix(pattern, "all:") {
-									includeHidden = true
-									matchPat = pattern[4:] // strip "all:" prefix
-								}
-								if matchPattern(matchPat, name, includeHidden) {
+							for _, ep := range allPatterns {
+								if matchPattern(ep.pattern, name, ep.includeHidden) {
 									p.EmbedGlobals[globalName] = append(p.EmbedGlobals[globalName], &EmbedFile{
 										Name:      name,
 										NeedsData: byteSlice,
@@ -651,8 +643,7 @@ func (p *Package) extractEmbedLines(addError func(error)) {
 
 // matchPattern returns true if (and only if) the given pattern would match the
 // filename. The pattern could also match a parent directory of name, in which
-// case hidden files do not match (unless includeHidden is true, which happens
-// when the pattern had an "all:" prefix).
+// case hidden files do not match (unless includeHidden is true).
 func matchPattern(pattern, name string, includeHidden bool) bool {
 	// Match this file.
 	matched, _ := path.Match(pattern, name)
@@ -690,13 +681,21 @@ func matchPattern(pattern, name string, includeHidden bool) bool {
 	}
 }
 
+// embedPattern represents a parsed //go:embed pattern.
+// The "all:" prefix (if present) is stripped and reflected in includeHidden.
+type embedPattern struct {
+	pattern       string // the glob pattern (without "all:" prefix)
+	includeHidden bool   // true if "all:" prefix was present
+}
+
 // parseGoEmbed is like strings.Fields but for a //go:embed line. It parses
 // regular fields and quoted fields (that may contain spaces).
-func (p *Package) parseGoEmbed(args string, pos token.Pos) (patterns []string, err error) {
+func (p *Package) parseGoEmbed(args string, pos token.Pos) (patterns []embedPattern, err error) {
 	args = strings.TrimSpace(args)
 	initialLen := len(args)
 	for args != "" {
 		patternPos := pos + token.Pos(initialLen-len(args))
+		var pattern string
 		switch args[0] {
 		case '`', '"', '\\':
 			// Parse the next pattern using the Go scanner.
@@ -715,8 +714,7 @@ func (p *Package) parseGoEmbed(args string, pos token.Pos) (patterns []string, e
 					Msg:  "invalid quoted string in //go:embed",
 				}
 			}
-			pattern := constant.StringVal(constant.MakeFromLiteral(lit, tok, 0))
-			patterns = append(patterns, pattern)
+			pattern = constant.StringVal(constant.MakeFromLiteral(lit, tok, 0))
 			args = strings.TrimLeftFunc(args[len(lit):], unicode.IsSpace)
 		default:
 			// The value is just a regular value.
@@ -725,23 +723,25 @@ func (p *Package) parseGoEmbed(args string, pos token.Pos) (patterns []string, e
 			if index < 0 {
 				index = len(args)
 			}
-			pattern := args[:index]
-			patterns = append(patterns, pattern)
+			pattern = args[:index]
 			args = strings.TrimLeftFunc(args[len(pattern):], unicode.IsSpace)
 		}
-		// Validate the pattern syntax. Strip "all:" prefix before validation
-		// since it's a directive, not part of the glob pattern.
-		validatePattern := patterns[len(patterns)-1]
-		if strings.HasPrefix(validatePattern, "all:") {
-			validatePattern = validatePattern[4:]
+		// Parse the "all:" prefix which includes hidden files.
+		// See: https://pkg.go.dev/embed#hdr-Directives
+		ep := embedPattern{pattern: pattern}
+		if strings.HasPrefix(pattern, "all:") {
+			ep.pattern = pattern[4:]
+			ep.includeHidden = true
 		}
-		if _, err := path.Match(validatePattern, ""); err != nil {
+		// Validate the pattern syntax.
+		if _, err := path.Match(ep.pattern, ""); err != nil {
 			return nil, types.Error{
 				Fset: p.program.fset,
 				Pos:  patternPos,
 				Msg:  "invalid pattern syntax",
 			}
 		}
+		patterns = append(patterns, ep)
 	}
 	return patterns, nil
 }