[parser] Recover missing identifier in new style typedef

Before, when parsing a new style typedef without an identifier (e.g.
`typedef = whatnot`) it concluded that the token after the equal-sign
wasn't an equal sign an that it thus had to be an old style typedef,
followed by recovery there.

This CL makes the recovery insert an identifier after `typedef` (what
the recovery of the old style actually did too), and then parse it as a
new style typedef.

This causes the previous many errors to just be `Expected an identifier,
but got '='.`

It is furthermore verified that the parsing of such a case is ~the same
as when having an indentifier.

Fixes #56912

Change-Id: I5cde1f29839555b1d6027a7d040dc6f60ac614a5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/392560
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Jens Johansen <[email protected]>

Author: jensjoha

pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart

@@ -721,6 +721,19 @@ class Parser {
             context.parseExtensionModifiers(modifierStart, keyword);
             return parseExtension(beginToken, context.augmentToken, keyword);
           }
+        } else if (identical(value, 'typedef')) {
+          // Having a method called typedef is ok, but we might also want to
+          // recover.
+          if (keyword.next!.endGroup?.next?.isA(TokenType.EQ) ?? false) {
+            // Recovery:
+            // `typedef` `<` [...] `>` `=`
+            // This isn't a legal method name. Assume we're missing the name of
+            // the typedef.
+            ModifierContext context = new ModifierContext(this);
+            context.parseTypedefModifiers(modifierStart, keyword);
+            directiveState?.checkDeclaration();
+            return parseTypedef(context.augmentToken, keyword);
+          }
         }
         directiveState?.checkDeclaration();
         return parseTopLevelMemberImpl(modifierStart);
@@ -1385,14 +1398,44 @@ class Parser {
     Token? equals;
     TypeParamOrArgInfo typeParam =
         computeTypeParamOrArg(next, /* inDeclaration = */ true);
-    if (typeInfo == noType && typeParam.skip(next).next!.isA(TokenType.EQ)) {
+    bool newStyle = false;
+    bool newStyleParseAsRecovered = false;
+    if (typeInfo == noType) {
+      Token skip = typeParam.skip(next);
+      if (skip.next!.isA(TokenType.EQ)) {
+        newStyle = true;
+
+        // Parse as recovered here to 'force' using it as an identifier as we've
+        // already established that the next token is the equal sign we're
+        // looking for.
+        newStyleParseAsRecovered = true;
+      } else if (skip.isA(TokenType.EQ)) {
+        // Recovery: `typedef =` insert missing identifier and parse as new
+        // style.
+        newStyle = true;
+        newStyleParseAsRecovered = false;
+      } else if (skip.isA(TokenType.LT)) {
+        if (skip.endGroup?.next?.isA(TokenType.EQ) ?? false) {
+          TypeParamOrArgInfo newTypeParam =
+              computeTypeParamOrArg(token, /* inDeclaration = */ true);
+          skip = newTypeParam.skip(token);
+          // This if shouldn't be necessary, but let's do it anyway.
+          if (skip.next!.isA(TokenType.EQ)) {
+            // Recovery: `typedef <whatever> =` insert missing identifier and
+            // parse as new style.
+            typeParam = newTypeParam;
+            newStyle = true;
+            newStyleParseAsRecovered = false;
+          }
+        }
+      }
+    }
+    if (newStyle) {
       // New style typedef, e.g. typedef foo = void Function();".
-
-      // Parse as recovered here to 'force' using it as an identifier as we've
-      // already established that the next token is the equal sign we're looking
-      // for.
-      token = ensureIdentifierPotentiallyRecovered(token,
-          IdentifierContext.typedefDeclaration, /* isRecovered = */ true);
+      token = ensureIdentifierPotentiallyRecovered(
+          token,
+          IdentifierContext.typedefDeclaration,
+          /* isRecovered = */ newStyleParseAsRecovered);
 
       token = typeParam.parseVariables(token, this);
       next = token.next!;

pkg/analyzer/test/src/dart/parser/type_alias_test.dart

@@ -61,30 +61,19 @@ GenericTypeAlias
 typedef = int;
 ''');
     parseResult.assertErrors([
-      error(ParserErrorCode.EXPECTED_TOKEN, 0, 7),
       error(ParserErrorCode.MISSING_IDENTIFIER, 8, 1),
-      error(ParserErrorCode.MISSING_TYPEDEF_PARAMETERS, 8, 1),
-      error(ParserErrorCode.EXPECTED_EXECUTABLE, 8, 1),
-      error(ParserErrorCode.MISSING_CONST_FINAL_VAR_OR_TYPE, 10, 3),
     ]);
 
     var node = parseResult.findNode.unit;
     assertParsedNodeText(node, r'''
 CompilationUnit
   declarations
-    FunctionTypeAlias
+    GenericTypeAlias
       typedefKeyword: typedef
       name: <empty> <synthetic>
-      parameters: FormalParameterList
-        leftParenthesis: ( <synthetic>
-        rightParenthesis: ) <synthetic>
-      semicolon: ; <synthetic>
-    TopLevelVariableDeclaration
-      variables: VariableDeclarationList
-        variables
-          VariableDeclaration
-            name: int
-      semicolon: ;
+      equals: =
+      type: NamedType
+        name: int
 ''');
   }
 }

pkg/analyzer/test/src/fasta/recovery/partial_code/typedef_test.dart

@@ -43,7 +43,7 @@ class TypedefTest extends PartialCodeTest {
                 ParserErrorCode.EXPECTED_TOKEN
               ],
               "typedef _s_ = _s_;",
-              allFailing: true),
+              failing: ['functionVoid', 'functionNonVoid', 'getter', 'mixin']),
           TestDescriptor(
               'equals',
               'typedef T =',

pkg/analyzer/test/src/summary/elements/type_alias_test.dart

@@ -6284,28 +6284,9 @@ library
     <testLibraryFragment>
       enclosingElement3: <null>
       typeAliases
-        functionTypeAliasBased @8
+        @8
           reference: <testLibraryFragment>::@typeAlias::0
-          aliasedType: dynamic Function()
-          aliasedElement: GenericFunctionTypeElement
-            returnType: dynamic
-      topLevelVariables
-        static int @10
-          reference: <testLibraryFragment>::@topLevelVariable::int
-          enclosingElement3: <testLibraryFragment>
-          type: dynamic
-      accessors
-        synthetic static get int @-1
-          reference: <testLibraryFragment>::@getter::int
-          enclosingElement3: <testLibraryFragment>
-          returnType: dynamic
-        synthetic static set int= @-1
-          reference: <testLibraryFragment>::@setter::int
-          enclosingElement3: <testLibraryFragment>
-          parameters
-            requiredPositional _int @-1
-              type: dynamic
-          returnType: void
+          aliasedType: int
 ----------------------------------------
 library
   reference: <testLibrary>
@@ -6316,42 +6297,10 @@ library
         <null-name>
           reference: <testLibraryFragment>::@typeAlias::0
           element: <testLibraryFragment>::@typeAlias::0#element
-      topLevelVariables
-        int @10
-          reference: <testLibraryFragment>::@topLevelVariable::int
-          element: <testLibraryFragment>::@topLevelVariable::int#element
-          getter2: <testLibraryFragment>::@getter::int
-          setter2: <testLibraryFragment>::@setter::int
-      getters
-        get <null-name>
-          reference: <testLibraryFragment>::@getter::int
-          element: <testLibraryFragment>::@getter::int#element
-      setters
-        set <null-name>
-          reference: <testLibraryFragment>::@setter::int
-          element: <testLibraryFragment>::@setter::int#element
-          formalParameters
-            <null-name>
-              element: <testLibraryFragment>::@setter::int::@parameter::_int#element
   typeAliases
     <null-name>
       firstFragment: <testLibraryFragment>::@typeAlias::0
-      aliasedType: dynamic Function()
-  topLevelVariables
-    int
-      firstFragment: <testLibraryFragment>::@topLevelVariable::int
-      type: dynamic
-      getter: <testLibraryFragment>::@getter::int#element
-      setter: <testLibraryFragment>::@setter::int#element
-  getters
-    synthetic static get int
-      firstFragment: <testLibraryFragment>::@getter::int
-  setters
-    synthetic static set int=
-      firstFragment: <testLibraryFragment>::@setter::int
-      formalParameters
-        requiredPositional _int
-          type: dynamic
+      aliasedType: int
 ''');
   }
 

pkg/front_end/parser_testcases/error_recovery/issue_56912.dart

@@ -0,0 +1 @@
+typedef = int;

pkg/front_end/parser_testcases/error_recovery/issue_56912.dart.expect

@@ -0,0 +1,20 @@
+Problems reported:
+
+parser/error_recovery/issue_56912:1:9: Expected an identifier, but got '='.
+typedef = int;
+        ^
+
+beginCompilationUnit(typedef)
+  beginMetadataStar(typedef)
+  endMetadataStar(0)
+  beginUncategorizedTopLevelDeclaration(typedef)
+    beginTypedef(typedef)
+      handleRecoverableError(Message[ExpectedIdentifier, Expected an identifier, but got '='., Try inserting an identifier before '='., {lexeme: =}], =, =)
+      handleIdentifier(, typedefDeclaration)
+      handleNoTypeVariables(=)
+      handleIdentifier(int, typeReference)
+      handleNoTypeArguments(;)
+      handleType(int, null)
+    endTypedef(null, typedef, =, ;)
+  endTopLevelDeclaration(;)
+endCompilationUnit(1, )

pkg/front_end/parser_testcases/error_recovery/issue_56912.dart.intertwined.expect

@@ -0,0 +1,27 @@
+parseUnit(typedef)
+  skipErrorTokens(typedef)
+  listener: beginCompilationUnit(typedef)
+  syntheticPreviousToken(typedef)
+  parseTopLevelDeclarationImpl(, DirectiveContext(DirectiveState.Unknown))
+    parseMetadataStar()
+      listener: beginMetadataStar(typedef)
+      listener: endMetadataStar(0)
+    parseTopLevelKeywordDeclaration(typedef, , typedef, null, null, null, null, DirectiveContext(DirectiveState.Unknown))
+      parseTypedef(null, typedef)
+        listener: beginUncategorizedTopLevelDeclaration(typedef)
+        listener: beginTypedef(typedef)
+        ensureIdentifierPotentiallyRecovered(typedef, typedefDeclaration, false)
+          insertSyntheticIdentifier(typedef, typedefDeclaration, message: Message[ExpectedIdentifier, Expected an identifier, but got '='., Try inserting an identifier before '='., {lexeme: =}], messageOnToken: null)
+            reportRecoverableError(=, Message[ExpectedIdentifier, Expected an identifier, but got '='., Try inserting an identifier before '='., {lexeme: =}])
+              listener: handleRecoverableError(Message[ExpectedIdentifier, Expected an identifier, but got '='., Try inserting an identifier before '='., {lexeme: =}], =, =)
+            rewriter()
+          listener: handleIdentifier(, typedefDeclaration)
+        listener: handleNoTypeVariables(=)
+        listener: handleIdentifier(int, typeReference)
+        listener: handleNoTypeArguments(;)
+        listener: handleType(int, null)
+        ensureSemicolon(int)
+        listener: endTypedef(null, typedef, =, ;)
+  listener: endTopLevelDeclaration(;)
+  reportAllErrorTokens(typedef)
+  listener: endCompilationUnit(1, )

pkg/front_end/parser_testcases/error_recovery/issue_56912.dart.parser.expect

@@ -0,0 +1,5 @@
+NOTICE: Stream was rewritten by parser!
+
+typedef *synthetic*= int;
+
+typedef[KeywordToken] [SyntheticStringToken]=[SimpleToken] int[StringToken];[SimpleToken][SimpleToken]

pkg/front_end/parser_testcases/error_recovery/issue_56912.dart.scanner.expect

@@ -0,0 +1,3 @@
+typedef = int;
+
+typedef[KeywordToken] =[SimpleToken] int[StringToken];[SimpleToken][SimpleToken]

pkg/front_end/parser_testcases/error_recovery/issue_56912.equivalence_info

@@ -0,0 +1,7 @@
+files:
+  - issue_56912.dart
+  - issue_56912_prime.dart
+filters:
+  - ignoreListenerArguments
+ignored:
+  - handleRecoverableError