parser: add specialized error for extension with descriptions (#3242)

Fixes #2568
Fixes #2385

Author: IvanGoncharov

src/language/__tests__/schema-parser-test.ts

@@ -340,8 +340,9 @@ describe('Schema Parser', () => {
         world: String
       }
     `).to.deep.equal({
-      message: 'Syntax Error: Unexpected Name "extend".',
-      locations: [{ line: 3, column: 7 }],
+      message:
+        'Syntax Error: Unexpected description, descriptions are supported only on type definitions.',
+      locations: [{ line: 2, column: 7 }],
     });
 
     expectSyntaxError(`
@@ -361,8 +362,9 @@ describe('Schema Parser', () => {
         world: String
       }
     `).to.deep.equal({
-      message: 'Syntax Error: Unexpected Name "extend".',
-      locations: [{ line: 3, column: 7 }],
+      message:
+        'Syntax Error: Unexpected description, descriptions are supported only on type definitions.',
+      locations: [{ line: 2, column: 7 }],
     });
 
     expectSyntaxError(`

src/language/parser.ts

@@ -41,7 +41,6 @@ import type {
   NamedTypeNode,
   ListTypeNode,
   NonNullTypeNode,
-  TypeSystemDefinitionNode,
   SchemaDefinitionNode,
   OperationTypeDefinitionNode,
   ScalarTypeDefinitionNode,
@@ -226,35 +225,72 @@ export class Parser {
    * ExecutableDefinition :
    *   - OperationDefinition
    *   - FragmentDefinition
+   *
+   * TypeSystemDefinition :
+   *   - SchemaDefinition
+   *   - TypeDefinition
+   *   - DirectiveDefinition
+   *
+   * TypeDefinition :
+   *   - ScalarTypeDefinition
+   *   - ObjectTypeDefinition
+   *   - InterfaceTypeDefinition
+   *   - UnionTypeDefinition
+   *   - EnumTypeDefinition
+   *   - InputObjectTypeDefinition
    */
   parseDefinition(): DefinitionNode {
-    if (this.peek(TokenKind.NAME)) {
-      switch (this._lexer.token.value) {
-        case 'query':
-        case 'mutation':
-        case 'subscription':
-          return this.parseOperationDefinition();
-        case 'fragment':
-          return this.parseFragmentDefinition();
+    if (this.peek(TokenKind.BRACE_L)) {
+      return this.parseOperationDefinition();
+    }
+
+    // Many definitions begin with a description and require a lookahead.
+    const hasDescription = this.peekDescription();
+    const keywordToken = hasDescription
+      ? this._lexer.lookahead()
+      : this._lexer.token;
+
+    if (keywordToken.kind === TokenKind.NAME) {
+      switch (keywordToken.value) {
         case 'schema':
+          return this.parseSchemaDefinition();
         case 'scalar':
+          return this.parseScalarTypeDefinition();
         case 'type':
+          return this.parseObjectTypeDefinition();
         case 'interface':
+          return this.parseInterfaceTypeDefinition();
         case 'union':
+          return this.parseUnionTypeDefinition();
         case 'enum':
+          return this.parseEnumTypeDefinition();
         case 'input':
+          return this.parseInputObjectTypeDefinition();
         case 'directive':
-          return this.parseTypeSystemDefinition();
+          return this.parseDirectiveDefinition();
+      }
+
+      if (hasDescription) {
+        throw syntaxError(
+          this._lexer.source,
+          this._lexer.token.start,
+          'Unexpected description, descriptions are supported only on type definitions.',
+        );
+      }
+
+      switch (keywordToken.value) {
+        case 'query':
+        case 'mutation':
+        case 'subscription':
+          return this.parseOperationDefinition();
+        case 'fragment':
+          return this.parseFragmentDefinition();
         case 'extend':
           return this.parseTypeSystemExtension();
       }
-    } else if (this.peek(TokenKind.BRACE_L)) {
-      return this.parseOperationDefinition();
-    } else if (this.peekDescription()) {
-      return this.parseTypeSystemDefinition();
     }
 
-    throw this.unexpected();
+    throw this.unexpected(keywordToken);
   }
 
   // Implements the parsing rules in the Operations section.
@@ -731,50 +767,6 @@ export class Parser {
 
   // Implements the parsing rules in the Type Definition section.
 
-  /**
-   * TypeSystemDefinition :
-   *   - SchemaDefinition
-   *   - TypeDefinition
-   *   - DirectiveDefinition
-   *
-   * TypeDefinition :
-   *   - ScalarTypeDefinition
-   *   - ObjectTypeDefinition
-   *   - InterfaceTypeDefinition
-   *   - UnionTypeDefinition
-   *   - EnumTypeDefinition
-   *   - InputObjectTypeDefinition
-   */
-  parseTypeSystemDefinition(): TypeSystemDefinitionNode {
-    // Many definitions begin with a description and require a lookahead.
-    const keywordToken = this.peekDescription()
-      ? this._lexer.lookahead()
-      : this._lexer.token;
-
-    if (keywordToken.kind === TokenKind.NAME) {
-      switch (keywordToken.value) {
-        case 'schema':
-          return this.parseSchemaDefinition();
-        case 'scalar':
-          return this.parseScalarTypeDefinition();
-        case 'type':
-          return this.parseObjectTypeDefinition();
-        case 'interface':
-          return this.parseInterfaceTypeDefinition();
-        case 'union':
-          return this.parseUnionTypeDefinition();
-        case 'enum':
-          return this.parseEnumTypeDefinition();
-        case 'input':
-          return this.parseInputObjectTypeDefinition();
-        case 'directive':
-          return this.parseDirectiveDefinition();
-      }
-    }
-
-    throw this.unexpected(keywordToken);
-  }
-
   peekDescription(): boolean {
     return this.peek(TokenKind.STRING) || this.peek(TokenKind.BLOCK_STRING);
   }