Fix .vercelignore negation patterns

file/glob.go

@@ -20,7 +20,16 @@ func GetPaths(basePath string, ignorePatterns []string) ([]string, error) {
 			if err != nil {
 				return err
 			}
-			ignored := ignore.MatchesPath(path)
+
+			relativePath, err := filepath.Rel(basePath, path)
+			if err != nil {
+				return fmt.Errorf("error finding path relative to base: %w", err)
+			}
+			if relativePath == "." {
+				return nil
+			}
+
+			ignored := ignore.MatchesPath(filepath.ToSlash(relativePath))
 
 			if d.IsDir() && ignored {
 				return filepath.SkipDir

file/glob_test.go

@@ -0,0 +1,86 @@
+package file
+
+import (
+	"os"
+	"path/filepath"
+	"slices"
+	"testing"
+)
+
+func TestGetPaths(t *testing.T) {
+	t.Parallel()
+
+	tests := map[string]struct {
+		files          []string
+		ignorePatterns []string
+		expected       []string
+	}{
+		"allowlist patterns": {
+			files: []string{
+				".vercelignore",
+				"api/example.js",
+				"example",
+				"index.html",
+				"main.tf",
+				"providers.tf",
+				"vercel.json",
+				"versions.tf",
+			},
+			ignorePatterns: []string{"/*", "!api", "!vercel.json", "!*.html"},
+			expected:       []string{"api/example.js", "index.html", "vercel.json"},
+		},
+		"root anchored pattern": {
+			files:          []string{"root.txt", "nested/root.txt", "nested/other.txt"},
+			ignorePatterns: []string{"/root.txt"},
+			expected:       []string{"nested/other.txt", "nested/root.txt"},
+		},
+	}
+
+	for name, test := range tests {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			root := t.TempDir()
+			workingDirectory, err := filepath.Abs(".")
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			for _, name := range test.files {
+				path := filepath.Join(root, name)
+				if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+					t.Fatal(err)
+				}
+				if err := os.WriteFile(path, nil, 0o644); err != nil {
+					t.Fatal(err)
+				}
+			}
+
+			relativeRoot, err := filepath.Rel(workingDirectory, root)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			for _, basePath := range []string{root, relativeRoot} {
+				paths, err := GetPaths(basePath, test.ignorePatterns)
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				actual := make([]string, 0, len(paths))
+				for _, path := range paths {
+					relativePath, err := filepath.Rel(basePath, path)
+					if err != nil {
+						t.Fatal(err)
+					}
+					actual = append(actual, filepath.ToSlash(relativePath))
+				}
+				slices.Sort(actual)
+
+				if !slices.Equal(actual, test.expected) {
+					t.Fatalf("GetPaths(%q) = %q, want %q", basePath, actual, test.expected)
+				}
+			}
+		})
+	}
+}