Fix panic in SkipTriviaEx when printing type predicates with declaration maps enabled

internal/scanner/issue1092_test.go

@@ -0,0 +1,49 @@
+package scanner
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/core"
+)
+
+// TestTypePredicate_Issue1092 tests the specific scenario that caused the panic in issue #1092
+// This test ensures that type predicates with declaration maps enabled do not cause panics
+func TestTypePredicate_Issue1092(t *testing.T) {
+	// The original problematic text that caused the slice bounds out of range panic
+	// This simulates the content from a declaration map that references a position beyond text bounds
+
+	shortText := "import { foo } from './export';\nexport const x = foo();"
+	textLen := len(shortText) // Should be 55 characters
+
+	// The original issue had pos=158 (or 167) but text length was 55/58
+	problematicPos := 158
+
+	// This should not panic - before the fix, this would cause:
+	// panic: runtime error: slice bounds out of range [158:55]
+	result := SkipTriviaEx(shortText, problematicPos, nil)
+
+	// The function should return the original position when it's beyond text bounds
+	if result != problematicPos {
+		t.Errorf("Expected position %d, got %d", problematicPos, result)
+	}
+
+	// Also test the GetLineAndCharacterOfPosition function that had a similar issue
+	sourceFile := &mockSourceFile{
+		text:    shortText,
+		lineMap: []core.TextPos{0, 27}, // Approximate line starts
+	}
+
+	// This should also not panic
+	line, char := GetLineAndCharacterOfPosition(sourceFile, problematicPos)
+
+	// We should get valid results (not negative numbers)
+	if line < 0 {
+		t.Errorf("Got negative line number: %d", line)
+	}
+	if char < 0 {
+		t.Errorf("Got negative character number: %d", char)
+	}
+
+	t.Logf("Successfully handled position %d beyond text length %d", problematicPos, textLen)
+	t.Logf("Computed line: %d, character: %d", line, char)
+}

internal/scanner/scanner.go

@@ -2094,6 +2094,9 @@ func SkipTriviaEx(text string, pos int, options *SkipTriviaOptions) int {
 	}
 
 	textLen := len(text)
+	if pos >= textLen {
+		return pos
+	}
 	canConsumeStar := false
 	// Keep in sync with couldStartTrivia
 	for {
@@ -2327,7 +2330,15 @@ func GetLineStarts(sourceFile ast.SourceFileLike) []core.TextPos {
 func GetLineAndCharacterOfPosition(sourceFile ast.SourceFileLike, pos int) (line int, character int) {
 	lineMap := GetLineStarts(sourceFile)
 	line = ComputeLineOfPosition(lineMap, pos)
-	character = utf8.RuneCountInString(sourceFile.Text()[lineMap[line]:pos])
+	textLen := len(sourceFile.Text())
+	startPos := int(lineMap[line])
+	if pos > textLen {
+		pos = textLen
+	}
+	if startPos > textLen {
+		startPos = textLen
+	}
+	character = utf8.RuneCountInString(sourceFile.Text()[startPos:pos])
 	return
 }
 

internal/scanner/scanner_test.go

@@ -0,0 +1,80 @@
+package scanner
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/core"
+)
+
+func TestSkipTriviaEx_BoundsCheck(t *testing.T) {
+	// Test with trivia (spaces and tabs)
+	text := "  \t hello"
+
+	// Test normal functionality - should skip leading whitespace
+	result := SkipTriviaEx(text, 0, nil)
+	if result != 4 { // Should skip 2 spaces and 1 tab to position 4 ('h')
+		t.Errorf("Expected position 4, got %d", result)
+	}
+
+	textLen := len(text) // 8 characters
+
+	// Test position at end of text
+	result = SkipTriviaEx(text, textLen, nil)
+	if result != textLen {
+		t.Errorf("Expected position %d, got %d", textLen, result)
+	}
+
+	// Test position beyond text bounds (should not panic)
+	result = SkipTriviaEx(text, textLen+10, nil)
+	if result != textLen+10 {
+		t.Errorf("Expected position %d, got %d", textLen+10, result)
+	}
+
+	// Test position way beyond text bounds (reproduces the original issue)
+	result = SkipTriviaEx(text, 158, nil)
+	if result != 158 {
+		t.Errorf("Expected position 158, got %d", result)
+	}
+}
+
+func TestGetLineAndCharacterOfPosition_BoundsCheck(t *testing.T) {
+	// Create a mock source file with a small text
+	sourceFile := &mockSourceFile{
+		text:    "hello\nworld",
+		lineMap: []core.TextPos{0, 6}, // Line 0 starts at 0, line 1 starts at 6
+	}
+
+	textLen := len(sourceFile.text) // 11 characters
+
+	// Test position within bounds
+	line, char := GetLineAndCharacterOfPosition(sourceFile, 7)
+	if line != 1 || char != 1 {
+		t.Errorf("Expected line 1, char 1, got line %d, char %d", line, char)
+	}
+
+	// Test position beyond text bounds (should not panic)
+	line, char = GetLineAndCharacterOfPosition(sourceFile, textLen+10)
+	if line < 0 {
+		t.Errorf("Expected valid line, got %d", line)
+	}
+
+	// Test the exact scenario from the bug report
+	line, char = GetLineAndCharacterOfPosition(sourceFile, 158)
+	if line < 0 {
+		t.Errorf("Expected valid line, got %d", line)
+	}
+}
+
+// Mock source file for testing
+type mockSourceFile struct {
+	text    string
+	lineMap []core.TextPos
+}
+
+func (m *mockSourceFile) Text() string {
+	return m.text
+}
+
+func (m *mockSourceFile) LineMap() []core.TextPos {
+	return m.lineMap
+}