fix: sync open files to disk before rename to prevent silent corruption

integrationtests/tests/rust/rename_symbol/stale_buffer_test.go

@@ -0,0 +1,90 @@
+package rename_symbol_test
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/isaacphi/mcp-language-server/integrationtests/tests/rust/internal"
+	"github.com/isaacphi/mcp-language-server/internal/tools"
+)
+
+// TestRenameSymbolStaleBuffer reproduces silent file corruption: when a file is
+// edited on disk by a non-LSP path after the server opened it, and a rename is
+// issued before the server's buffer is re-synced, the server plans the
+// WorkspaceEdit against its stale (pre-edit) buffer. Those ranges point at where
+// references used to be; applied to the now-larger on-disk file they overwrite
+// unrelated text and miss the real references, while the tool reports success.
+//
+// It runs the real configuration (watcher ON). rust-analyzer is warmed first so
+// the rename completes in ~1ms, far inside the watcher's 300ms debounce, and wins
+// the race exactly as in production. The ~200x margin keeps it deterministic: if
+// the rename ever lost the race it fails loudly with ContentModified rather than
+// flake. A correct bridge must sync open files to disk before renaming.
+func TestRenameSymbolStaleBuffer(t *testing.T) {
+	suite := internal.GetTestSuite(t)
+
+	ctx, cancel := context.WithTimeout(suite.Context, 30*time.Second)
+	defer cancel()
+
+	for _, f := range []string{
+		"src/main.rs", "src/types.rs", "src/helper.rs",
+		"src/consumer.rs", "src/another_consumer.rs", "src/clean.rs",
+	} {
+		if err := suite.Client.OpenFile(ctx, filepath.Join(suite.WorkspaceDir, f)); err != nil {
+			t.Logf("open %s: %v", f, err)
+		}
+	}
+	time.Sleep(3 * time.Second)
+
+	// Force rust-analyzer's first (slow) analysis now so the timed rename is fast.
+	for i := 0; i < 3; i++ {
+		if _, err := tools.FindReferences(ctx, suite.Client, "SHARED_CONSTANT"); err != nil {
+			t.Logf("warm-up references: %v", err)
+		}
+	}
+
+	consumerPath := filepath.Join(suite.WorkspaceDir, "src/consumer.rs")
+	original, err := os.ReadFile(consumerPath)
+	if err != nil {
+		t.Fatalf("read consumer.rs: %v", err)
+	}
+
+	// Edit consumer.rs on disk without notifying the server: prepend marker lines
+	// so every SHARED_CONSTANT reference shifts down, off the server's stale view.
+	const markerCount = 8
+	var markers strings.Builder
+	for i := 0; i < markerCount; i++ {
+		fmt.Fprintf(&markers, "// REPRO MARKER %d - must be preserved verbatim\n", i)
+	}
+	if err := os.WriteFile(consumerPath, append([]byte(markers.String()), original...), 0644); err != nil {
+		t.Fatalf("write consumer.rs: %v", err)
+	}
+
+	// Rename the constant at its definition in types.rs (line 78, col 11).
+	typesPath := filepath.Join(suite.WorkspaceDir, "src/types.rs")
+	t0 := time.Now()
+	result, err := tools.RenameSymbol(ctx, suite.Client, typesPath, 78, 11, "RENAMED_CONSTANT")
+	t.Logf("rename took %v (watcher debounce is 300ms)", time.Since(t0))
+	if err != nil {
+		t.Fatalf("RenameSymbol returned error (likely ContentModified, watcher beat the rename): %v", err)
+	}
+	t.Logf("rename result: %s", result)
+
+	got, err := os.ReadFile(consumerPath)
+	if err != nil {
+		t.Fatalf("re-read consumer.rs: %v", err)
+	}
+	gotStr := string(got)
+
+	// A correct rename replaces both SHARED_CONSTANT references and touches nothing
+	// else; any other bytes are the stale-position corruption.
+	want := markers.String() + strings.ReplaceAll(string(original), "SHARED_CONSTANT", "RENAMED_CONSTANT")
+	if gotStr != want {
+		t.Errorf("consumer.rs corrupted by a stale-position rename.\n--- got ---\n%s\n--- want ---\n%s", gotStr, want)
+	}
+}

internal/lsp/client.go

@@ -366,6 +366,27 @@ func (c *Client) NotifyChange(ctx context.Context, filepath string) error {
 	return c.Notify(ctx, "textDocument/didChange", params)
 }
 
+// SyncOpenFiles re-sends every open file's current on-disk content to the server
+// via didChange. Callers that plan edits from the server's view of a document
+// must call this first (see RenameSymbol).
+func (c *Client) SyncOpenFiles(ctx context.Context) {
+	c.openFilesMu.RLock()
+	uris := make([]string, 0, len(c.openFiles))
+	for uri := range c.openFiles {
+		uris = append(uris, uri)
+	}
+	c.openFilesMu.RUnlock()
+
+	for _, uri := range uris {
+		path := strings.TrimPrefix(uri, "file://")
+		if err := c.NotifyChange(ctx, path); err != nil {
+			// Unreadable (e.g. deleted): leave it stale. ApplyWorkspaceEdit will
+			// then error on it rather than corrupt it.
+			lspLogger.Debug("SyncOpenFiles: skipping %s: %v", path, err)
+		}
+	}
+}
+
 func (c *Client) CloseFile(ctx context.Context, filepath string) error {
 	uri := fmt.Sprintf("file://%s", filepath)
 

internal/tools/rename-symbol.go

@@ -39,6 +39,11 @@ func RenameSymbol(ctx context.Context, client *lsp.Client, filePath string, line
 	// Skip the PrepareRename check as it might not be supported by all language servers
 	// Execute the rename directly
 
+	// Sync the server's view of every open file to disk before planning the
+	// rename: an out-of-band on-disk edit after the file was opened otherwise
+	// leaves a stale buffer, and the rename's ranges land at stale positions.
+	client.SyncOpenFiles(ctx)
+
 	// Execute the rename operation
 	workspaceEdit, err := client.Rename(ctx, params)
 	if err != nil {