fix(lsp): parse LocationLink in definition results

We advertise textDocument.definition.linkSupport=true, so gopls and rust-analyzer return the LocationLink shape (targetUri/targetRange). The old code only tried []Location then a single Location; unmarshaling LocationLink JSON into []Location silently succeeds with zero-value URIs/ranges, producing garbage locations (or a false 'No definition found'). parseDefinitionResult now decodes a unified shape capturing both field sets and normalizes to Location, and surfaces a real parse error instead of swallowing it. Adds TestParseDefinitionResult covering all shapes.

internal/lsp/definition_parse_test.go

@@ -0,0 +1,78 @@
+package lsp
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+// TestParseDefinitionResult covers every LSP definition result shape: single
+// Location, Location[], single LocationLink, LocationLink[], plus empty/error
+// cases. The LocationLink shapes are the regression target — we advertise
+// LinkSupport, so gopls/rust-analyzer return targetUri/targetRange, which a
+// naive []Location unmarshal would silently turn into zero-value locations.
+func TestParseDefinitionResult(t *testing.T) {
+	tests := []struct {
+		name     string
+		raw      string
+		wantURIs []string
+		wantErr  bool
+	}{
+		{
+			name:     "single Location",
+			raw:      `{"uri":"file:///a.go","range":{"start":{"line":4,"character":2},"end":{"line":4,"character":8}}}`,
+			wantURIs: []string{"file:///a.go"},
+		},
+		{
+			name:     "Location array",
+			raw:      `[{"uri":"file:///a.go","range":{"start":{"line":1,"character":0},"end":{"line":1,"character":3}}},{"uri":"file:///b.go","range":{"start":{"line":2,"character":0},"end":{"line":2,"character":3}}}]`,
+			wantURIs: []string{"file:///a.go", "file:///b.go"},
+		},
+		{
+			name:     "single LocationLink",
+			raw:      `{"targetUri":"file:///c.go","targetRange":{"start":{"line":9,"character":0},"end":{"line":12,"character":1}}}`,
+			wantURIs: []string{"file:///c.go"},
+		},
+		{
+			name:     "LocationLink array",
+			raw:      `[{"targetUri":"file:///d.go","targetRange":{"start":{"line":0,"character":0},"end":{"line":0,"character":5}}}]`,
+			wantURIs: []string{"file:///d.go"},
+		},
+		{
+			name:     "empty array",
+			raw:      `[]`,
+			wantURIs: []string{},
+		},
+		{
+			name:    "garbage",
+			raw:     `"not-a-location"`,
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			locs, err := parseDefinitionResult(json.RawMessage(tt.raw))
+			if tt.wantErr {
+				if err == nil {
+					t.Fatalf("expected error, got locations %+v", locs)
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if len(locs) != len(tt.wantURIs) {
+				t.Fatalf("got %d locations, want %d (%+v)", len(locs), len(tt.wantURIs), locs)
+			}
+			for i, want := range tt.wantURIs {
+				if locs[i].URI != want {
+					t.Errorf("location[%d].URI = %q, want %q", i, locs[i].URI, want)
+				}
+			}
+			// LocationLink ranges must be carried over, not zeroed.
+			if tt.name == "single LocationLink" && locs[0].Range.Start.Line != 9 {
+				t.Errorf("LocationLink targetRange not preserved: got start line %d, want 9", locs[0].Range.Start.Line)
+			}
+		})
+	}
+}

internal/lsp/manager.go

@@ -358,17 +358,55 @@ func (m *Manager) Definition(ctx context.Context, file string, line, col int) ([
 		return nil, nil
 	}
 
-	// Result can be Location, []Location, or []LocationLink
-	var locations []Location
-	if err := json.Unmarshal(resp.Result, &locations); err != nil {
-		// Try single location
-		var single Location
-		if err := json.Unmarshal(resp.Result, &single); err == nil {
-			locations = []Location{single}
+	return parseDefinitionResult(resp.Result)
+}
+
+// parseDefinitionResult decodes a textDocument/definition result. Per LSP the
+// result may be Location, Location[], LocationLink, or LocationLink[]. Because
+// we advertise LinkSupport (see initialize), servers such as gopls and
+// rust-analyzer return the LocationLink shape (targetUri/targetRange). A naive
+// unmarshal into []Location silently succeeds with zero-value URIs/ranges, so
+// decode into a unified shape that captures both and normalize to Location.
+func parseDefinitionResult(raw json.RawMessage) ([]Location, error) {
+	// locOrLink captures both the Location (uri/range) and LocationLink
+	// (targetUri/targetRange) field sets; whichever is populated wins.
+	type locOrLink struct {
+		URI         string `json:"uri"`
+		Range       Range  `json:"range"`
+		TargetURI   string `json:"targetUri"`
+		TargetRange Range  `json:"targetRange"`
+	}
+	toLocation := func(l locOrLink) (Location, bool) {
+		if l.URI != "" {
+			return Location{URI: l.URI, Range: l.Range}, true
 		}
+		if l.TargetURI != "" {
+			return Location{URI: l.TargetURI, Range: l.TargetRange}, true
+		}
+		return Location{}, false
 	}
 
-	return locations, nil
+	// Array form (Location[] or LocationLink[]).
+	var arr []locOrLink
+	if err := json.Unmarshal(raw, &arr); err == nil {
+		locations := make([]Location, 0, len(arr))
+		for _, l := range arr {
+			if loc, ok := toLocation(l); ok {
+				locations = append(locations, loc)
+			}
+		}
+		return locations, nil
+	}
+
+	// Single object form (Location or LocationLink).
+	var single locOrLink
+	if err := json.Unmarshal(raw, &single); err != nil {
+		return nil, fmt.Errorf("failed to parse definition result: %w", err)
+	}
+	if loc, ok := toLocation(single); ok {
+		return []Location{loc}, nil
+	}
+	return nil, nil
 }
 
 // References finds all references to the symbol at the given position.