lsp: add textDocument/documentHighlight support

Implement document highlight by reusing the references query and
filtering results to only include occurrences within the same file.
This matches the approach used by Sourcegraph's web client.

Author: jupblb

cmd/src/lsp.go

@@ -25,6 +25,7 @@ Supported LSP methods:
   - textDocument/definition
   - textDocument/references
   - textDocument/hover
+  - textDocument/documentHighlight
 
 Example Neovim configuration (0.11+):
 

internal/lsp/server.go

@@ -52,9 +52,10 @@ func (s *Server) Run() error {
 		SetTrace:               s.handleSetTrace,
 		TextDocumentDidOpen:    s.handleTextDocumentDidOpen,
 		TextDocumentDidClose:   s.handleTextDocumentDidClose,
-		TextDocumentDefinition: s.handleTextDocumentDefinition,
-		TextDocumentReferences: s.handleTextDocumentReferences,
-		TextDocumentHover:      s.handleTextDocumentHover,
+		TextDocumentDefinition:        s.handleTextDocumentDefinition,
+		TextDocumentReferences:        s.handleTextDocumentReferences,
+		TextDocumentHover:             s.handleTextDocumentHover,
+		TextDocumentDocumentHighlight: s.handleTextDocumentDocumentHighlight,
 	}
 
 	srv := server.NewServer(&handler, serverName, false)
@@ -67,9 +68,10 @@ func (s *Server) handleInitialize(_ *glsp.Context, _ *protocol.InitializeParams)
 			TextDocumentSync: &protocol.TextDocumentSyncOptions{
 				OpenClose: &protocol.True,
 			},
-			DefinitionProvider: true,
-			ReferencesProvider: true,
-			HoverProvider:      true,
+			DefinitionProvider:        true,
+			ReferencesProvider:        true,
+			HoverProvider:             true,
+			DocumentHighlightProvider: true,
 		},
 		ServerInfo: &protocol.InitializeResultServerInfo{
 			Name:    serverName,
@@ -237,6 +239,50 @@ func (s *Server) handleTextDocumentHover(_ *glsp.Context, params *protocol.Hover
 	return hover, nil
 }
 
+func (s *Server) handleTextDocumentDocumentHighlight(_ *glsp.Context, params *protocol.DocumentHighlightParams) ([]protocol.DocumentHighlight, error) {
+	path, err := s.uriToRepoPath(params.TextDocument.URI)
+	if err != nil {
+		return nil, err
+	}
+
+	nodes, err := s.queryReferences(context.Background(), path, int(params.Position.Line), int(params.Position.Character))
+	if err != nil {
+		return nil, err
+	}
+	if len(nodes) == 0 {
+		return nil, nil
+	}
+
+	var highlights []protocol.DocumentHighlight
+	for _, node := range nodes {
+		if node.Resource.Repository.Name != s.repoName {
+			continue
+		}
+		if node.Resource.Path != path {
+			continue
+		}
+
+		highlights = append(highlights, protocol.DocumentHighlight{
+			Range: protocol.Range{
+				Start: protocol.Position{
+					Line:      protocol.UInteger(node.Range.Start.Line),
+					Character: protocol.UInteger(node.Range.Start.Character),
+				},
+				End: protocol.Position{
+					Line:      protocol.UInteger(node.Range.End.Line),
+					Character: protocol.UInteger(node.Range.End.Character),
+				},
+			},
+		})
+	}
+
+	if len(highlights) == 0 {
+		return nil, nil
+	}
+
+	return highlights, nil
+}
+
 func (s *Server) uriToRepoPath(uri string) (string, error) {
 	parsed, err := url.Parse(uri)
 	if err != nil {

internal/lsp/server_test.go

@@ -1,10 +1,14 @@
 package lsp
 
 import (
+	"context"
 	"os"
 	"path/filepath"
 	"testing"
 
+	protocol "github.com/tliron/glsp/protocol_3_16"
+
+	"github.com/sourcegraph/src-cli/internal/api/mock"
 	"github.com/stretchr/testify/require"
 )
 
@@ -88,3 +92,197 @@ func TestRunGitCommandError(t *testing.T) {
 	require.Error(t, err)
 	require.Contains(t, err.Error(), "git command failed")
 }
+
+func TestHandleTextDocumentDocumentHighlight(t *testing.T) {
+	gitRoot, err := getGitRoot()
+	require.NoError(t, err)
+
+	tests := []struct {
+		name          string
+		path          string
+		response      string
+		wantCount     int
+		wantNil       bool
+	}{
+		{
+			name: "filters to same file only",
+			path: "main.go",
+			response: `{
+				"repository": {
+					"commit": {
+						"blob": {
+							"lsif": {
+								"references": {
+									"nodes": [
+										{
+											"resource": {
+												"path": "main.go",
+												"repository": {"name": "github.com/test/repo"},
+												"commit": {"oid": "abc123"}
+											},
+											"range": {
+												"start": {"line": 10, "character": 0},
+												"end": {"line": 10, "character": 5}
+											}
+										},
+										{
+											"resource": {
+												"path": "main.go",
+												"repository": {"name": "github.com/test/repo"},
+												"commit": {"oid": "abc123"}
+											},
+											"range": {
+												"start": {"line": 20, "character": 0},
+												"end": {"line": 20, "character": 5}
+											}
+										},
+										{
+											"resource": {
+												"path": "other.go",
+												"repository": {"name": "github.com/test/repo"},
+												"commit": {"oid": "abc123"}
+											},
+											"range": {
+												"start": {"line": 5, "character": 0},
+												"end": {"line": 5, "character": 5}
+											}
+										}
+									]
+								}
+							}
+						}
+					}
+				}
+			}`,
+			wantCount: 2,
+		},
+		{
+			name: "filters out other repositories",
+			path: "main.go",
+			response: `{
+				"repository": {
+					"commit": {
+						"blob": {
+							"lsif": {
+								"references": {
+									"nodes": [
+										{
+											"resource": {
+												"path": "main.go",
+												"repository": {"name": "github.com/test/repo"},
+												"commit": {"oid": "abc123"}
+											},
+											"range": {
+												"start": {"line": 10, "character": 0},
+												"end": {"line": 10, "character": 5}
+											}
+										},
+										{
+											"resource": {
+												"path": "main.go",
+												"repository": {"name": "github.com/other/repo"},
+												"commit": {"oid": "def456"}
+											},
+											"range": {
+												"start": {"line": 15, "character": 0},
+												"end": {"line": 15, "character": 5}
+											}
+										}
+									]
+								}
+							}
+						}
+					}
+				}
+			}`,
+			wantCount: 1,
+		},
+		{
+			name: "no references returns nil",
+			path: "main.go",
+			response: `{
+				"repository": {
+					"commit": {
+						"blob": {
+							"lsif": {
+								"references": {
+									"nodes": []
+								}
+							}
+						}
+					}
+				}
+			}`,
+			wantNil: true,
+		},
+		{
+			name: "all references in other files returns nil",
+			path: "main.go",
+			response: `{
+				"repository": {
+					"commit": {
+						"blob": {
+							"lsif": {
+								"references": {
+									"nodes": [
+										{
+											"resource": {
+												"path": "other.go",
+												"repository": {"name": "github.com/test/repo"},
+												"commit": {"oid": "abc123"}
+											},
+											"range": {
+												"start": {"line": 10, "character": 0},
+												"end": {"line": 10, "character": 5}
+											}
+										}
+									]
+								}
+							}
+						}
+					}
+				}
+			}`,
+			wantNil: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockClient := &mock.Client{}
+			mockRequest := &mock.Request{Response: tt.response}
+			mockRequest.On("Do", context.Background(), &referencesResponse{}).Return(true, nil)
+			mockClient.On("NewRequest", referencesQuery, map[string]any{
+				"repository": "github.com/test/repo",
+				"commit":     "abc123",
+				"path":       tt.path,
+				"line":       10,
+				"character":  5,
+			}).Return(mockRequest)
+
+			s := &Server{
+				apiClient: mockClient,
+				repoName:  "github.com/test/repo",
+				commit:    "abc123",
+			}
+
+			uri := "file://" + filepath.Join(gitRoot, tt.path)
+			params := &protocol.DocumentHighlightParams{
+				TextDocumentPositionParams: protocol.TextDocumentPositionParams{
+					TextDocument: protocol.TextDocumentIdentifier{URI: uri},
+					Position:     protocol.Position{Line: 10, Character: 5},
+				},
+			}
+
+			result, err := s.handleTextDocumentDocumentHighlight(nil, params)
+			require.NoError(t, err)
+
+			if tt.wantNil {
+				require.Nil(t, result)
+				return
+			}
+
+			require.Len(t, result, tt.wantCount)
+		})
+	}
+}