feat: Add filename search support

cmd/dcs-web/search/query-rewrite.go

@@ -8,8 +8,10 @@ import (
 )
 
 var (
-	start = regexp.MustCompile(`(?i)^\s*(-?(?:filetype|package|pkg|path|file)):(\S+)\s+`)
-	end   = regexp.MustCompile(`(?i)\s+(-?(?:filetype|package|pkg|path|file)):(\S+)\s*$`)
+	start = regexp.MustCompile(`(?i)^\s*(-?(?:filetype|package|pkg|path|file|filename)):(\S+)\s+`)
+	end   = regexp.MustCompile(`(?i)\s+(-?(?:filetype|package|pkg|path|file|filename)):(\S+)\s*$`)
+	// solo matches when the entire query is just a single keyword:value (no other search terms)
+	solo = regexp.MustCompile(`(?i)^\s*(-?(?:filetype|package|pkg|path|file|filename)):(\S+)\s*$`)
 )
 
 func rewriteFilters(query url.Values, filtersRe *regexp.Regexp) url.Values {
@@ -37,6 +39,9 @@ func rewriteFilters(query url.Values, filtersRe *regexp.Regexp) url.Values {
 
 		if filtersRe == start {
 			qstr = strings.TrimPrefix(qstr, matches[0])
+		} else if filtersRe == solo {
+			// For solo matches, the entire query string is consumed
+			qstr = ""
 		} else {
 			qstr = strings.TrimSuffix(qstr, matches[0])
 		}
@@ -53,6 +58,8 @@ func RewriteQuery(u url.URL) url.URL {
 	// query is a copy which we will modify using Set() and use in the result
 	query := rewriteFilters(u.Query(), start)
 	query = rewriteFilters(query, end)
+	// Handle queries that are only a single keyword (no content search term)
+	query = rewriteFilters(query, solo)
 	u.RawQuery = query.Encode()
 
 	return u

cmd/dcs-web/search/query-rewrite_test.go

@@ -161,4 +161,27 @@ func TestRewriteQuery(t *testing.T) {
 	if seen != 2 {
 		t.Fatalf("Expected two elements in the hash of the -package keyword, saw %d", seen)
 	}
+
+	// Verify that filename: keyword is recognized
+	rewritten = rewrite(t, "/search?q=filename:CMakeLists.txt")
+	if filename := rewritten.Query().Get("filename"); filename != "CMakeLists.txt" {
+		t.Fatalf("Expected filename %q, got %q", "CMakeLists.txt", filename)
+	}
+
+	// Verify that filename: keyword with regex is parsed correctly
+	// Note: + is URL-encoded as %2B since + in URLs means space
+	rewritten = rewrite(t, "/search?q=filename:debian/.%2B\\.doc-base.*")
+	if filename := rewritten.Query().Get("filename"); filename != "debian/.+\\.doc-base.*" {
+		t.Fatalf("Expected filename %q, got %q", "debian/.+\\.doc-base.*", filename)
+	}
+
+	// Verify that filename: keyword can be combined with content search
+	rewritten = rewrite(t, "/search?q=searchterm+filename:Makefile")
+	querystr = rewritten.Query().Get("q")
+	if querystr != "searchterm" {
+		t.Fatalf("Expected search query %q, got %q", "searchterm", querystr)
+	}
+	if filename := rewritten.Query().Get("filename"); filename != "Makefile" {
+		t.Fatalf("Expected filename %q, got %q", "Makefile", filename)
+	}
 }

internal/index/read.go

@@ -81,6 +81,27 @@ func (dr *DocidReader) Lookup(docid uint32) (string, error) {
 	return dr.last.fn, nil
 }
 
+// ForEachFilename iterates over all filenames in the index and calls the
+// callback function for each one. If the callback returns an error, iteration
+// stops and the error is returned. The docid is passed along with each filename.
+func (dr *DocidReader) ForEachFilename(fn func(docid uint32, filename string) error) error {
+	data := dr.f.Data[:dr.indexOffset]
+	var docid uint32
+	start := 0
+	for i := 0; i < len(data); i++ {
+		if data[i] == '\n' {
+			filename := string(data[start:i])
+			if err := fn(docid, filename); err != nil {
+				return err
+			}
+			docid++
+			start = i + 1
+		}
+	}
+	return nil
+}
+
+
 type reusableBuffer struct {
 	u []uint32
 }

internal/sourcebackend/sourcebackend.go

@@ -146,6 +146,51 @@ type Server struct {
 	UsePositionalIndex bool
 }
 
+// FilenameMatch represents a single filename match result
+type FilenameMatch struct {
+	Path        string  // Full path including package
+	PackageName string  // Source package name
+	Ranking     float32 // Ranking score for ordering results
+}
+
+// SearchFilenames searches for files matching the given filename pattern regex.
+// Returns all matching file paths without searching file contents.
+func (s *Server) SearchFilenames(pattern string) ([]FilenameMatch, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+
+	filenameRegexp, err := regexp.Compile(pattern)
+	if err != nil {
+		return nil, fmt.Errorf("invalid filename pattern: %v", err)
+	}
+
+	var matches []FilenameMatch
+
+	err = s.Index.DocidMap.ForEachFilename(func(docid uint32, filename string) error {
+		if filenameRegexp.MatchString(filename, true, true) != -1 {
+			// Extract package name (first path component before /)
+			pkgName := filename
+			if idx := strings.Index(filename, "/"); idx != -1 {
+				pkgName = filename[:idx]
+			}
+
+			matches = append(matches, FilenameMatch{
+				Path:        filename,
+				PackageName: pkgName,
+				Ranking:     1.0, // Default ranking, could be enhanced based on match position
+			})
+		}
+		return nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	return matches, nil
+}
+
+
 // Serves a single file for displaying it in /show
 func (s *Server) File(ctx context.Context, in *sourcebackendpb.FileRequest) (*sourcebackendpb.FileReply, error) {
 	log.Printf("requested filename *%s*\n", in.Path)