Add WithSkipEmptySourceMaps parser option

parser/parser.go

@@ -53,6 +53,7 @@ const (
 
 type options struct {
 	disableSourceMaps bool
+	skipEmptySourceMaps bool
 	sourceMapLoader   func(path string) ([]byte, error)
 }
 
@@ -66,6 +67,13 @@ func WithDisableSourceMaps(opts *options) {
 	opts.disableSourceMaps = true
 }
 
+// WithSkipEmptySourceMaps is an option to ignore source maps that are empty rather than fail parsing.
+// This is particulary useful for code compiled from TypeScript. The TypeScript compiler outputs empty
+// source maps for files containing only type definitions.
+func WithSkipEmptySourceMaps(opts *options) {
+	opts.skipEmptySourceMaps = true
+}
+
 // WithSourceMapLoader is an option to set a custom source map loader. The loader will be given a path or a
 // URL from the sourceMappingURL. If sourceMappingURL is not absolute it is resolved relatively to the name
 // of the file being parsed. Any error returned by the loader will fail the parsing.

parser/parser_test.go

@@ -1235,6 +1235,25 @@ var x = {};
 		is(err, nil)
 		is(count, 1)
 		is(requestedPath, "https://site.com/delme.js.map")
+
+		// Checks related to empty source maps.
+		emptySourceMapLoader := func(p string) ([]byte, error) {
+			count++
+			requestedPath = p
+			emptySourceMap := `{"version":3,"file":"delme.js","sourceRoot":"","sources":["../src/delme.ts"],"names":[],"mappings":""}`
+			return []byte(emptySourceMap), nil
+		}
+
+		// First, ensure that the expected error is produced for an empty source map.
+		_, err = ParseFile(nil, "delme.js", src, 0, WithSourceMapLoader(emptySourceMapLoader))
+		is(true, strings.Contains(err.Error(), errSourceMapEmptyString))
+
+		// Then, ensure WithSkipEmptySourceMaps bypasses the error.
+		count = 0
+		_, err = ParseFile(nil, "delme.js", src, 0, WithSourceMapLoader(emptySourceMapLoader), WithSkipEmptySourceMaps)
+		is(err, nil)
+		is(count, 1)
+		is(requestedPath, "delme.js.map")
 	})
 }
 

parser/statement.go

@@ -12,6 +12,11 @@ import (
 	"github.com/go-sourcemap/sourcemap"
 )
 
+const (
+	// Copied from https://github.com/go-sourcemap/sourcemap/blob/794171861aeb0f83fcd66eeb0415a5062594cde6/mappings.go#L35
+	errSourceMapEmptyString = "sourcemap: mappings are empty"
+)
+
 func (self *_parser) parseBlockStatement() *ast.BlockStatement {
 	node := &ast.BlockStatement{}
 	node.LeftBrace = self.expect(token.LEFT_BRACE)
@@ -950,6 +955,8 @@ func (self *_parser) parseSourceMap() *sourcemap.Consumer {
 
 		if sm, err := sourcemap.Parse(self.file.Name(), data); err == nil {
 			return sm
+		} else if self.opts.skipEmptySourceMaps && strings.Contains(err.Error(), errSourceMapEmptyString) {
+			return nil
 		} else {
 			self.error(file.Idx(0), "Could not parse source map: %v", err)
 		}