basic support for parsing import attributes

CHANGELOG.md

@@ -131,6 +131,24 @@
       this error and leave the unresolved path in the bundle.
     ```
 
+* Parse and print the `with` keyword in `import` statements
+
+    JavaScript was going to have a feature called "import assertions" that adds an `assert` keyword to `import` statements. It looked like this:
+
+    ```js
+    import stuff from './stuff.json' assert { type: 'json' }
+    ```
+
+    The feature provided a way to assert that the imported file is of a certain type (but was not allowed to affect how the import is interpreted, even though that's how everyone expected it to behave). The feature was fully specified and then actually implemented and shipped in Chrome before the people behind the feature realized that they should allow it to affect how the import is interpreted after all. So import assertions are no longer going to be added to the language.
+
+    Instead, the [current proposal](https://github.com/tc39/proposal-import-attributes) is to add a feature called "import attributes" instead that adds a `with` keyword to import statements. It looks like this:
+
+    ```js
+    import stuff from './stuff.json' with { type: 'json' }
+    ```
+
+    This feature provides a way to affect how the import is interpreted. With this release, esbuild now has preliminary support for parsing and printing this new `with` keyword. The `with` keyword is not yet interpreted by esbuild, however, so bundling code with it will generate a build error. All this release does is allow you to use esbuild to process code containing it (such as removing types from TypeScript code). Note that this syntax is not yet a part of JavaScript and may be removed or altered in the future if the specification changes (which it already has once, as described above). If that happens, esbuild reserves the right to remove or alter its support for this syntax too.
+
 ## 0.19.2
 
 * Update how CSS nesting is parsed again

compat-table/src/index.ts

@@ -57,6 +57,7 @@ export const jsFeatures = {
   Generator: true,
   Hashbang: true,
   ImportAssertions: true,
+  ImportAttributes: true,
   ImportMeta: true,
   InlineScript: true,
   LogicalAssignment: true,

internal/ast/ast.go

@@ -149,10 +149,10 @@ func (flags ImportRecordFlags) Has(flag ImportRecordFlags) bool {
 }
 
 type ImportRecord struct {
-	Assertions  *ImportAssertions
-	GlobPattern *GlobPattern
-	Path        logger.Path
-	Range       logger.Range
+	AssertOrWith *ImportAssertOrWith
+	GlobPattern  *GlobPattern
+	Path         logger.Path
+	Range        logger.Range
 
 	// If the "HandlesImportErrors" flag is present, then this is the location
 	// of the error handler. This is used for error reporting.
@@ -170,24 +170,39 @@ type ImportRecord struct {
 	Kind  ImportKind
 }
 
-type ImportAssertions struct {
-	Entries            []AssertEntry
-	AssertLoc          logger.Loc
+type AssertOrWithKeyword uint8
+
+const (
+	AssertKeyword AssertOrWithKeyword = iota
+	WithKeyword
+)
+
+func (kw AssertOrWithKeyword) String() string {
+	if kw == AssertKeyword {
+		return "assert"
+	}
+	return "with"
+}
+
+type ImportAssertOrWith struct {
+	Entries            []AssertOrWithEntry
+	KeywordLoc         logger.Loc
 	InnerOpenBraceLoc  logger.Loc
 	InnerCloseBraceLoc logger.Loc
 	OuterOpenBraceLoc  logger.Loc
 	OuterCloseBraceLoc logger.Loc
+	Keyword            AssertOrWithKeyword
 }
 
-type AssertEntry struct {
+type AssertOrWithEntry struct {
 	Key             []uint16 // An identifier or a string
 	Value           []uint16 // Always a string
 	KeyLoc          logger.Loc
 	ValueLoc        logger.Loc
 	PreferQuotedKey bool
 }
 
-func FindAssertion(assertions []AssertEntry, name string) *AssertEntry {
+func FindAssertOrWithEntry(assertions []AssertOrWithEntry, name string) *AssertOrWithEntry {
 	for _, assertion := range assertions {
 		if helpers.UTF16EqualsString(assertion.Key, name) {
 			return &assertion

internal/bundler/bundler.go

@@ -380,6 +380,13 @@ func parseFile(args parseArgs) {
 						continue
 					}
 
+					// TODO: Implement bundling with import attributes
+					if record.AssertOrWith != nil && record.AssertOrWith.Keyword == ast.WithKeyword {
+						args.log.AddError(&tracker, js_lexer.RangeOfIdentifier(result.file.inputFile.Source, record.AssertOrWith.KeywordLoc),
+							"Bundling with import attributes is not currently supported")
+						continue
+					}
+
 					// Special-case glob pattern imports
 					if record.GlobPattern != nil {
 						prettyPath := helpers.GlobPatternToString(record.GlobPattern.Parts)
@@ -1962,7 +1969,7 @@ func (s *scanner) scanAllDependencies() {
 						sourceIndex := s.allocateGlobSourceIndex(result.file.inputFile.Source.Index, uint32(importRecordIndex))
 						record.SourceIndex = ast.MakeIndex32(sourceIndex)
 						s.results[sourceIndex] = s.generateResultForGlobResolve(sourceIndex, globResults.absPath,
-							&result.file.inputFile.Source, record.Range, record.GlobPattern.Kind, globResults, record.Assertions)
+							&result.file.inputFile.Source, record.Range, record.GlobPattern.Kind, globResults, record.AssertOrWith)
 					}
 					continue
 				}
@@ -2010,7 +2017,7 @@ func (s *scanner) generateResultForGlobResolve(
 	importRange logger.Range,
 	kind ast.ImportKind,
 	result globResolveResult,
-	assertions *ast.ImportAssertions,
+	assertions *ast.ImportAssertOrWith,
 ) parseResult {
 	keys := make([]string, 0, len(result.resolveResults))
 	for key := range result.resolveResults {
@@ -2057,10 +2064,10 @@ func (s *scanner) generateResultForGlobResolve(
 
 		resolveResults = append(resolveResults, &resolveResult)
 		importRecords = append(importRecords, ast.ImportRecord{
-			Path:        path,
-			SourceIndex: sourceIndex,
-			Assertions:  assertions,
-			Kind:        kind,
+			Path:         path,
+			SourceIndex:  sourceIndex,
+			AssertOrWith: assertions,
+			Kind:         kind,
 		})
 
 		switch kind {
@@ -2203,7 +2210,7 @@ func (s *scanner) processScannedFiles(entryPointMeta []graph.EntryPoint) []scann
 					s.log.AddErrorWithNotes(&tracker, record.Range,
 						fmt.Sprintf("The file %q was loaded with the %q loader", otherFile.inputFile.Source.PrettyPath, config.LoaderToString[otherFile.inputFile.Loader]),
 						[]logger.MsgData{
-							tracker.MsgData(js_lexer.RangeOfImportAssertion(result.file.inputFile.Source, *ast.FindAssertion(record.Assertions.Entries, "type")),
+							tracker.MsgData(js_lexer.RangeOfImportAssertOrWith(result.file.inputFile.Source, *ast.FindAssertOrWithEntry(record.AssertOrWith.Entries, "type")),
 								"This import assertion requires the loader to be \"json\" instead:"),
 							{Text: "You need to either reconfigure esbuild to ensure that the loader for this file is \"json\" or you need to remove this import assertion."}})
 				}

internal/bundler_tests/bundler_loader_test.go

@@ -1537,3 +1537,23 @@ func TestLoaderCopyWithInjectedFileBundle(t *testing.T) {
 		},
 	})
 }
+
+func TestLoaderBundleWithImportAttributes(t *testing.T) {
+	loader_suite.expectBundled(t, bundled{
+		files: map[string]string{
+			"/entry.js": `
+				import x from "./import.js"
+				import y from "./import.js" with { type: 'json' }
+				console.log(x === y)
+			`,
+			"/import.js": `{}`,
+		},
+		entryPaths: []string{"/entry.js"},
+		options: config.Options{
+			Mode:          config.ModeBundle,
+			AbsOutputFile: "/out.js",
+		},
+		expectedScanLog: `entry.js: ERROR: Bundling with import attributes is not currently supported
+`,
+	})
+}

internal/compat/js_table.go

@@ -90,6 +90,7 @@ const (
 	Generator
 	Hashbang
 	ImportAssertions
+	ImportAttributes
 	ImportMeta
 	InlineScript
 	LogicalAssignment
@@ -149,6 +150,7 @@ var StringToJSFeature = map[string]JSFeature{
 	"generator":                         Generator,
 	"hashbang":                          Hashbang,
 	"import-assertions":                 ImportAssertions,
+	"import-attributes":                 ImportAttributes,
 	"import-meta":                       ImportMeta,
 	"inline-script":                     InlineScript,
 	"logical-assignment":                LogicalAssignment,
@@ -504,6 +506,7 @@ var jsTable = map[JSFeature]map[Engine][]versionRange{
 		Edge:   {{start: v{91, 0, 0}}},
 		Node:   {{start: v{16, 14, 0}}},
 	},
+	ImportAttributes: {},
 	ImportMeta: {
 		Chrome:  {{start: v{64, 0, 0}}},
 		Deno:    {{start: v{1, 0, 0}}},

internal/graph/graph.go

@@ -195,7 +195,7 @@ func CloneLinkerGraph(
 							// For example, "import('./foo.json', { assert: { type: 'json' } })"
 							// will likely be converted into an import of a JavaScript file and
 							// leaving the import assertion there will prevent it from working.
-							record.Assertions = nil
+							record.AssertOrWith = nil
 						}
 					}
 				}

internal/js_lexer/js_lexer.go

@@ -673,9 +673,9 @@ func RangeOfIdentifier(source logger.Source, loc logger.Loc) logger.Range {
 	return source.RangeOfString(loc)
 }
 
-func RangeOfImportAssertion(source logger.Source, assertion ast.AssertEntry) logger.Range {
-	loc := RangeOfIdentifier(source, assertion.KeyLoc).Loc
-	return logger.Range{Loc: loc, Len: source.RangeOfString(assertion.ValueLoc).End() - loc.Start}
+func RangeOfImportAssertOrWith(source logger.Source, assertOrWith ast.AssertOrWithEntry) logger.Range {
+	loc := RangeOfIdentifier(source, assertOrWith.KeyLoc).Loc
+	return logger.Range{Loc: loc, Len: source.RangeOfString(assertOrWith.ValueLoc).End() - loc.Start}
 }
 
 func (lexer *Lexer) ExpectJSXElementChild(token T) {