Revert support for simple nullable type return value in generalized function type

This reverts commit 11d081d115

Reason for revert: Breaks parsing less common conditionals (e.g. b ? c = true : g();)

Original change's description:
> Add support for simple nullable type return value in generalized function type
>
> This only supports nullable return values of the form
>
> <identifier> '?' 'Function' '(' ...
>
> This is an increment CL in the ongoing effort to add nullable type support
> as outlined in https://github.com/dart-lang/language/issues/110

Change-Id: I99bce29619d4e448193e3c81fa86a982791b1f77
Reviewed-on: https://dart-review.googlesource.com/c/87283
Reviewed-by: Dan Rubel <danrubel@google.com>

pkg/analyzer/test/generated/parser_test.dart

@@ -2013,46 +2013,6 @@ mixin ComplexParserTestMixin implements AbstractParserTestCase {
     expect(elseExpression, new TypeMatcher<SimpleIdentifier>());
   }
 
-  void test_conditionalExpression_precedence_nullableTypeWithTypeArg1_is() {
-    Expression expression = parseExpression('x is String<S> ? (x + y) : z');
-    expect(expression, isNotNull);
-    expect(expression, new TypeMatcher<ConditionalExpression>());
-    ConditionalExpression conditional = expression;
-    Expression condition = conditional.condition;
-    expect(condition, new TypeMatcher<IsExpression>());
-    Expression thenExpression = conditional.thenExpression;
-    expect(thenExpression, new TypeMatcher<ParenthesizedExpression>());
-    Expression elseExpression = conditional.elseExpression;
-    expect(elseExpression, new TypeMatcher<SimpleIdentifier>());
-  }
-
-  void test_conditionalExpression_precedence_nullableTypeWithTypeArg1GFT_is() {
-    Expression expression =
-        parseExpression('x is String<S> Function() ? (x + y) : z');
-    expect(expression, isNotNull);
-    expect(expression, new TypeMatcher<ConditionalExpression>());
-    ConditionalExpression conditional = expression;
-    Expression condition = conditional.condition;
-    expect(condition, new TypeMatcher<IsExpression>());
-    Expression thenExpression = conditional.thenExpression;
-    expect(thenExpression, new TypeMatcher<ParenthesizedExpression>());
-    Expression elseExpression = conditional.elseExpression;
-    expect(elseExpression, new TypeMatcher<SimpleIdentifier>());
-  }
-
-  void test_conditionalExpression_precedence_nullableTypeWithTypeArg2_is() {
-    Expression expression = parseExpression('x is String<S,T> ? (x + y) : z');
-    expect(expression, isNotNull);
-    expect(expression, new TypeMatcher<ConditionalExpression>());
-    ConditionalExpression conditional = expression;
-    Expression condition = conditional.condition;
-    expect(condition, new TypeMatcher<IsExpression>());
-    Expression thenExpression = conditional.thenExpression;
-    expect(thenExpression, new TypeMatcher<ParenthesizedExpression>());
-    Expression elseExpression = conditional.elseExpression;
-    expect(elseExpression, new TypeMatcher<SimpleIdentifier>());
-  }
-
   void test_constructor_initializer_withParenthesizedExpression() {
     CompilationUnit unit = parseCompilationUnit(r'''
 class C {

pkg/front_end/lib/src/fasta/parser/type_info.dart

@@ -187,7 +187,7 @@ TypeInfo computeType(final Token token, bool required,
   if (isGeneralizedFunctionType(next)) {
     // `Function` ...
     return new ComplexTypeInfo(token, noTypeParamOrArg)
-        .computeNoTypeGFT(token, required);
+        .computeNoTypeGFT(required);
   }
 
   // We've seen an identifier.
@@ -262,17 +262,20 @@ TypeInfo computeType(final Token token, bool required,
   }
 
   if (optional('?', next)) {
-    next = next.next;
-    if (isGeneralizedFunctionType(next)) {
-      // identifier `?` Function `(`
-      return new ComplexTypeInfo(token, noTypeParamOrArg)
-          .computeIdentifierQuestionGFT(required);
-    } else if (required ||
-        (looksLikeName(next) &&
-            isOneOfOrEof(
-                next.next, const [';', ',', '=', '>', '>=', '>>', '>>>']))) {
+    if (required) {
       // identifier `?`
       return simpleNullableType;
+    } else {
+      next = next.next;
+      if (isGeneralizedFunctionType(next)) {
+        // identifier `?` Function `(`
+        return simpleNullableType;
+      } else if (looksLikeName(next) &&
+          isOneOfOrEof(
+              next.next, const [';', ',', '=', '>', '>=', '>>', '>>>'])) {
+        // identifier `?` identifier `=`
+        return simpleNullableType;
+      }
     }
   } else if (required || looksLikeName(next)) {
     // identifier identifier

pkg/front_end/lib/src/fasta/parser/type_info_impl.dart

@@ -376,9 +376,6 @@ class ComplexTypeInfo implements TypeInfo {
   /// Type arguments were seen during analysis.
   final TypeParamOrArgInfo typeArguments;
 
-  /// The token before the trailing question mark or `null` if none.
-  Token beforeQuestionMark;
-
   /// The last token in the type reference.
   Token end;
 
@@ -393,18 +390,12 @@ class ComplexTypeInfo implements TypeInfo {
   ComplexTypeInfo(Token beforeStart, this.typeArguments)
       : this.start = beforeStart.next;
 
-  ComplexTypeInfo._nonNullable(this.start, this.typeArguments, this.end,
-      this.typeVariableStarters, this.gftHasReturnType);
-
   @override
   bool get couldBeExpression => false;
 
   @override
   TypeInfo asNonNullableType() {
-    return beforeQuestionMark == null
-        ? this
-        : new ComplexTypeInfo._nonNullable(start, typeArguments,
-            beforeQuestionMark, typeVariableStarters, gftHasReturnType);
+    return this;
   }
 
   @override
@@ -461,15 +452,7 @@ class ComplexTypeInfo implements TypeInfo {
           }
         }
         token = typeArguments.parseArguments(token, parser);
-        Token questionMark = token.next;
-        if (optional('?', questionMark) &&
-            (typeVariableEndGroups.isNotEmpty || beforeQuestionMark != null)) {
-          // Only consume the `?` if it is part of the complex type
-          token = questionMark;
-        } else {
-          questionMark = null;
-        }
-        parser.listener.handleType(typeRefOrPrefix, questionMark);
+        parser.listener.handleType(typeRefOrPrefix, null);
       }
     }
 
@@ -509,11 +492,10 @@ class ComplexTypeInfo implements TypeInfo {
 
   /// Given `Function` non-identifier, compute the type
   /// and return the receiver or one of the [TypeInfo] constants.
-  TypeInfo computeNoTypeGFT(Token beforeStart, bool required) {
+  TypeInfo computeNoTypeGFT(bool required) {
     assert(optional('Function', start));
-    assert(beforeStart.next == start);
 
-    computeRest(beforeStart, required);
+    computeRest(start, required);
     if (gftHasReturnType == null) {
       return required ? simpleType : noType;
     }
@@ -527,7 +509,7 @@ class ComplexTypeInfo implements TypeInfo {
     assert(optional('void', start));
     assert(optional('Function', start.next));
 
-    computeRest(start, required);
+    computeRest(start.next, required);
     if (gftHasReturnType == null) {
       return voidType;
     }
@@ -541,7 +523,7 @@ class ComplexTypeInfo implements TypeInfo {
     assert(isValidTypeReference(start));
     assert(optional('Function', start.next));
 
-    computeRest(start, required);
+    computeRest(start.next, required);
     if (gftHasReturnType == null) {
       return simpleType;
     }
@@ -549,28 +531,13 @@ class ComplexTypeInfo implements TypeInfo {
     return this;
   }
 
-  /// Given identifier `?` `Function` non-identifier, compute the type
-  /// and return the receiver or one of the [TypeInfo] constants.
-  TypeInfo computeIdentifierQuestionGFT(bool required) {
-    assert(isValidTypeReference(start));
-    assert(optional('?', start.next));
-    assert(optional('Function', start.next.next));
-
-    computeRest(start, required);
-    if (gftHasReturnType == null) {
-      return simpleNullableType;
-    }
-    assert(end != null);
-    return this;
-  }
-
   /// Given a builtin, return the receiver so that parseType will report
   /// an error for the builtin used as a type.
   TypeInfo computeBuiltinOrVarAsType(bool required) {
     assert(start.type.isBuiltIn || optional('var', start));
 
     end = typeArguments.skip(start);
-    computeRest(end, required);
+    computeRest(end.next, required);
     assert(end != null);
     return this;
   }
@@ -583,7 +550,7 @@ class ComplexTypeInfo implements TypeInfo {
     assert(typeArguments != noTypeParamOrArg);
 
     end = typeArguments.skip(start);
-    computeRest(end, required);
+    computeRest(end.next, required);
 
     if (!required && !looksLikeName(end.next) && gftHasReturnType == null) {
       return noType;
@@ -607,7 +574,7 @@ class ComplexTypeInfo implements TypeInfo {
     }
 
     end = typeArguments.skip(token);
-    computeRest(end, required);
+    computeRest(end.next, required);
     if (!required && !looksLikeName(end.next) && gftHasReturnType == null) {
       return noType;
     }
@@ -616,11 +583,6 @@ class ComplexTypeInfo implements TypeInfo {
   }
 
   void computeRest(Token token, bool required) {
-    if (optional('?', token.next)) {
-      beforeQuestionMark = token;
-      end = token = token.next;
-    }
-    token = token.next;
     while (optional('Function', token)) {
       Token typeVariableStart = token;
       // TODO(danrubel): Consider caching TypeParamOrArgInfo
@@ -641,14 +603,9 @@ class ComplexTypeInfo implements TypeInfo {
       assert(optional(')', token));
       gftHasReturnType ??= typeVariableStart != start;
       typeVariableStarters = typeVariableStarters.prepend(typeVariableStart);
-      beforeQuestionMark = null;
       end = token;
       token = token.next;
     }
-    if (optional('?', token)) {
-      beforeQuestionMark = end;
-      end = token;
-    }
   }
 }
 

pkg/front_end/test/fasta/parser/type_info_test.dart

@@ -800,19 +800,6 @@ class TypeInfoTest {
         ]);
   }
 
-  void test_computeType_identifierComplex_questionMark() {
-    expectComplexInfo('C? Function()', required: true, expectedCalls: [
-      'handleNoTypeVariables (',
-      'beginFunctionType C',
-      'handleIdentifier C typeReference',
-      'handleNoTypeArguments ?',
-      'handleType C ?',
-      'beginFormalParameters ( MemberKind.GeneralizedFunctionType',
-      'endFormalParameters 0 ( ) MemberKind.GeneralizedFunctionType',
-      'endFunctionType Function null',
-    ]);
-  }
-
   void test_computeType_identifierTypeArg() {
     expectComplexInfo('C<void>', required: true, expectedCalls: [
       'handleIdentifier C typeReference',