Add a node to InvalidGenerationSourceError (#670)

Allow attempting to find the source location from an AstNode as an
alternative to finding it from an Element.

Author: natebosch

source_gen/CHANGELOG.md

@@ -1,6 +1,8 @@
-## 1.3.3-wip
+## 1.4.0-wip
 
 - Require Dart 3.0
+- Add a `node` argument to `InvalidGenerationSourceError` to allow finding the
+  source location from an `AstNode` over an `Element`.
 
 ## 1.3.2
 

source_gen/lib/src/generator.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:build/build.dart';
 
@@ -41,18 +42,30 @@ class InvalidGenerationSourceError extends Error {
 
   /// The code element associated with this error.
   ///
-  /// May be `null` if the error had no associated element.
+  /// May be `null` if the error had no associated element, or if the location
+  /// was passed with [node].
   final Element? element;
 
-  InvalidGenerationSourceError(this.message, {this.todo = '', this.element});
+  /// The AST Node associated with this error.
+  ///
+  /// May be `null` if the error has no associated node in the input source
+  /// code, or if the location was passed with [element].
+  final AstNode? node;
+
+  InvalidGenerationSourceError(
+    this.message, {
+    this.todo = '',
+    this.element,
+    this.node,
+  });
 
   @override
   String toString() {
     final buffer = StringBuffer(message);
 
-    if (element != null) {
+    if (element case final element?) {
       try {
-        final span = spanForElement(element!);
+        final span = spanForElement(element);
         buffer
           ..writeln()
           ..writeln(span.start.toolString)
@@ -66,6 +79,20 @@ class InvalidGenerationSourceError extends Error {
       }
     }
 
+    if (node case final node?) {
+      try {
+        final span = spanForNode(node);
+        buffer
+          ..writeln()
+          ..writeln(span.start.toolString)
+          ..write(span.highlight());
+      } catch (_) {
+        buffer
+          ..writeln()
+          ..writeln('Cause: $node');
+      }
+    }
+
     return buffer.toString();
   }
 }

source_gen/lib/src/span_for_element.dart

@@ -2,6 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:source_span/source_span.dart';
 
@@ -51,3 +52,13 @@ SourceSpan spanForElement(Element element, [SourceFile? file]) {
 
   return file.span(element.nameOffset, element.nameOffset + element.nameLength);
 }
+
+/// Returns a source span that spans the location where [node] is written.
+SourceSpan spanForNode(AstNode node) {
+  final unit = node.thisOrAncestorOfType<CompilationUnit>()!;
+  final element = unit.declaredElement!;
+  final contents = element.source.contents.data;
+  final url = assetToPackageUrl(element.source.uri);
+  final file = SourceFile.fromString(contents, url: url);
+  return file.span(node.offset, node.offset + node.length);
+}

source_gen/pubspec.yaml

@@ -1,5 +1,5 @@
 name: source_gen
-version: 1.3.3-wip
+version: 1.4.0-wip
 description: >-
   Source code generation builders and utilities for the Dart build system
 repository: https://github.com/dart-lang/source_gen/tree/master/source_gen

source_gen/test/span_for_element_test.dart

@@ -5,13 +5,14 @@
 import 'package:analyzer/dart/element/element.dart';
 import 'package:build/build.dart';
 import 'package:build_test/build_test.dart';
-import 'package:source_gen/source_gen.dart';
+import 'package:source_gen/src/span_for_element.dart';
 import 'package:term_glyph/term_glyph.dart' as glyph;
 import 'package:test/test.dart';
 
 void main() {
   glyph.ascii = true;
   late LibraryElement library;
+  late Resolver resolver;
 
   setUpAll(() async {
     library = await resolveSource(
@@ -28,7 +29,10 @@ abstract class Example implements List {
   }
 }
 ''',
-      (resolver) async => (await resolver.findLibraryByName('test_lib'))!,
+      (r) async {
+        resolver = r;
+        return (await resolver.findLibraryByName('test_lib'))!;
+      },
       inputId: AssetId('test_lib', 'lib/test_lib.dart'),
     );
   });
@@ -96,4 +100,18 @@ line 7, column 11 of package:test_lib/test_lib.dart: Here it is
   '""",
     );
   });
+
+  test('highlights based on AstNode source location', () async {
+    final element = library.getClass('Example')!.getField('field')!.declaration;
+    final node = (await resolver.astNodeFor(element, resolve: true))!;
+    expect(
+      spanForNode(node).message('Here it is'),
+      r"""
+line 6, column 7 of package:test_lib/test_lib.dart: Here it is
+  ,
+6 |   int field;
+  |       ^^^^^
+  '""",
+    );
+  });
 }