Non-internal API for accessing ElementAnnotation source ranges

[MichaelRFairhurst]

If someone uses an annotation wrong,

@Directive(...) // but I forgot to import angular!
class ... { ... }

then the ElementAnnotation for this cannot compute constant value, and has no element.

To aid creators of tools such as angular, the element model should contain a source range for the element annotation so that Angular can attempt to help the user in this case, rather than just having some 'null's in their program that could mean anything at all.

+@matanlurey says he could use this change to remove some instances of computeNode().

[matanlurey]

Thanks!

This is for dart-lang/source_gen#316:

  // TODO: Remove internal API once ElementAnnotation has source information.
  // https://github.com/dart-lang/sdk/issues/32454
  static SourceSpan _getSourceSpanFrom(ElementAnnotation annotation) {
    final internals = annotation as ElementAnnotationImpl;
    final astNode = internals.annotationAst;
    final contents = annotation.source.contents.data;
    final start = astNode.offset;
    final end = start + astNode.length;
    return new SourceSpan(
      new SourceLocation(start, sourceUrl: annotation.source.uri),
      new SourceLocation(end, sourceUrl: annotation.source.uri),
      contents.substring(start, end),
    );
  }

[bwilkerson]

@MichaelRFairhurst Is this still relevant?

[MichaelRFairhurst]

Looks like yes, source_gen has a src import from analyzer to work around this: https://github.com/dart-lang/source_gen/blob/master/source_gen/lib/src/type_checker.dart#L12. Assuming we want to fix that...

[natebosch]

This might also be giving us trouble in the migration to analysis driver, some details of the workaround in source_gen could be broken.

Any chance we can get a nicer and backwards/forwards compatible API for this?

[stereotype441]

We discussed this and found a different way to achieve the same result: by having the angular compiler retrieve the ResolvedLibraryResult after an error occurs, and find annotation's AST inside it in order to get the source range.

So we no longer need a special API for this.

[matanlurey]

Chatted internally with @natebosch - despite this being marked fixed I actually don't see how I can access the ResolvedLibraryResult object or migrate off of using src/ for package:analyzer, which was what this ticket was originally about. Here is a reference to our current code:

import 'package:analyzer/dart/element/element.dart';
// ignore: implementation_imports
import 'package:analyzer/src/dart/element/element.dart';

class BuildError {
  /// Creates a build error using the provided source annotation as [context].
  factory BuildError.forAnnotation(
    ElementAnnotation context,
    String message,
  ) {
    // TOOD(b/170758395): Replace w/ patches from upstream (see pkg/source_gen).
    // https://github.com/dart-lang/sdk/issues/32454
    final annotation = context as ElementAnnotationImpl;
    final astNode = annotation.annotationAst;
    final file = SourceFile.fromString(
      annotation.source.contents.data,
      url: annotation.source.uri,
    );
    return BuildError.forSourceSpan(
      file.span(astNode.offset, astNode.offset + astNode.length),
      message,
    );
  }
}