Skip to content

Improve error recovery for incomplete attribute in a type-parameter. #81231

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
CyrusNajmabadi merged 15 commits into from
Nov 18, 2025
Merged

Improve error recovery for incomplete attribute in a type-parameter. #81231

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
15 commits
Select commit Hold shift + click to select a range
3a09a5d
Initial plan
Copilot Nov 11, 2025
c780868
Implement attribute target filtering for IntelliSense
Copilot Nov 11, 2025
a95e595
Cache ValidAttributeTargets to avoid expensive recomputation
Copilot Nov 11, 2025
51cfa91
Update src/Workspaces/SharedUtilitiesAndExtensions/Workspace/CSharp/E…
CyrusNajmabadi Nov 11, 2025
bd67526
Add comprehensive tests and use pattern matching improvements
Copilot Nov 11, 2025
8fc6527
Add tests
CyrusNajmabadi Nov 11, 2025
0a0d8ce
Update parser
CyrusNajmabadi Nov 11, 2025
78d6908
Use 'field'
CyrusNajmabadi Nov 11, 2025
13d6ec2
Update logic and add tests
CyrusNajmabadi Nov 12, 2025
286d305
More precise check
CyrusNajmabadi Nov 12, 2025
01e2862
Simplify
CyrusNajmabadi Nov 12, 2025
92b1b54
Merge branch 'main' into copilot/update-intellisense-attribute-filter…
CyrusNajmabadi Nov 14, 2025
acd2b5b
Add tests
CyrusNajmabadi Nov 14, 2025
8a38ae5
Merge remote-tracking branch 'upstream/main' into copilot/update-inte…
CyrusNajmabadi Nov 18, 2025
fd5d3d1
Add tests
CyrusNajmabadi Nov 18, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
26 changes: 12 additions & 14 deletions src/Compilers/CSharp/Portable/Parser/LanguageParser.cs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -6028,36 +6028,34 @@ private bool IsStartOfTypeParameter()
if (this.IsCurrentTokenWhereOfConstraintClause())
return false;

// possible attributes
if (this.CurrentToken.Kind == SyntaxKind.OpenBracketToken && this.PeekToken(1).Kind != SyntaxKind.CloseBracketToken)
Copy link
Member Author

@CyrusNajmabadi CyrusNajmabadi Nov 14, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

this blocks good error recovery in the Foo<[]T> case. There isn't a good reason for this, as [] isn't a suitable start of some other construct. In all other attribute cases, running into [] is supported, just not for type params.

This simply removes that restriction, and gives consistent support for attributes here like everywhere else.

return true;

// possible attributes.
// Variance.
if (this.CurrentToken.Kind is SyntaxKind.InKeyword or SyntaxKind.OutKeyword)
if (this.CurrentToken.Kind is SyntaxKind.OpenBracketToken or SyntaxKind.InKeyword or SyntaxKind.OutKeyword)
return true;

return IsTrueIdentifier();
}

private TypeParameterSyntax ParseTypeParameter()
{
if (this.IsCurrentTokenWhereOfConstraintClause())
{
return _syntaxFactory.TypeParameter(
default(SyntaxList<AttributeListSyntax>),
varianceKeyword: null,
this.AddError(CreateMissingIdentifierToken(), ErrorCode.ERR_IdentifierExpected));
}

var attrs = default(SyntaxList<AttributeListSyntax>);
if (this.CurrentToken.Kind == SyntaxKind.OpenBracketToken && this.PeekToken(1).Kind != SyntaxKind.CloseBracketToken)
if (this.CurrentToken.Kind == SyntaxKind.OpenBracketToken)
{
var saveTerm = _termState;
_termState = TerminatorState.IsEndOfTypeArgumentList;
attrs = this.ParseAttributeDeclarations(inExpressionContext: false);
_termState = saveTerm;
}

if (this.IsCurrentTokenWhereOfConstraintClause() ||
this.IsCurrentTokenPartialKeywordOfPartialMemberOrType())
Copy link
Member

@jcouv jcouv Nov 18, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

It's not obvious why "partial" is getting special treatment. Should we similarly care about other modifier keywords?

Copy link
Member Author

@CyrusNajmabadi CyrusNajmabadi Nov 18, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

partial/where refer to the special identifiers that IsTrueIdentifier returns false for if it sees that these should not actually be treated as identifiers but as contextual keywords.

They're treated specially here as they are very reasonable contextual keywords that would follow a type param being written.

{
return _syntaxFactory.TypeParameter(
attrs,
varianceKeyword: null,
this.AddError(CreateMissingIdentifierToken(), ErrorCode.ERR_IdentifierExpected));
}

return _syntaxFactory.TypeParameter(
attrs,
this.CurrentToken.Kind is SyntaxKind.InKeyword or SyntaxKind.OutKeyword ? EatToken() : null,
Expand Down
Loading