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Improve error messages for keywords used as identifiers in LINQ let clauses #80695

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c4db6de
Initial plan
Copilot Oct 14, 2025
ebea297
Improve error messages for keywords in LINQ let clauses
Copilot Oct 14, 2025
fe41692
Refactor: Extract IsReservedKeywordFollowedByEquals method
Copilot Oct 14, 2025
570ed57
Inline IsReservedKeywordFollowedByEquals method
Copilot Oct 14, 2025
2ce564d
Use conditional expression and EatTokenAsKind
Copilot Oct 14, 2025
48b2070
Fix test
CyrusNajmabadi Oct 14, 2025
a939446
lint
CyrusNajmabadi Oct 14, 2025
9406664
Fix blank lines with whitespace and update contributing docs
Copilot Oct 14, 2025
31f7835
Apply suggestions from code review
CyrusNajmabadi Oct 14, 2025
000650f
Update .github/copilot-instructions.md
CyrusNajmabadi Oct 14, 2025
31069dc
Fix QueryWithMultipleParseErrorsAndScriptParseOption test
Copilot Oct 14, 2025
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12 changes: 10 additions & 2 deletions src/Compilers/CSharp/Portable/Parser/LanguageParser.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -13904,9 +13904,17 @@ private JoinClauseSyntax ParseJoinClause()
private LetClauseSyntax ParseLetClause()
{
Debug.Assert(this.CurrentToken.ContextualKind == SyntaxKind.LetKeyword);
var letKeyword = this.EatContextualToken(SyntaxKind.LetKeyword);

Check failure on line 13908 in src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

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src/Compilers/CSharp/Portable/Parser/LanguageParser.cs#L13908 

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs(13908,1): error IDE0055: (NETCORE_ENGINEERING_TELEMETRY=Build) Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055)

Check failure on line 13908 in src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

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Azure Pipelines / roslyn-CI (Correctness Correctness_Analyzers)

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs#L13908 

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs(13908,1): error IDE0055: (NETCORE_ENGINEERING_TELEMETRY=Build) Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055)
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@copilot Roslyn disallows blank lines with spaces on them. Please update the copilot contributing document to mention that this should be avoided as it will cause linting errors that will have to be fixed up.

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Done in commit 2ce564d. Fixed the blank lines with spaces in ParseLetClause and updated .github/copilot-instructions.md to include a note about this requirement under the Formatting section.

// If we see a keyword followed by '=', use EatTokenAsKind to produce
// a better error message (ERR_IdentifierExpectedKW) and recover well.
var identifier = SyntaxFacts.IsReservedKeyword(this.CurrentToken.Kind) && this.PeekToken(1).Kind == SyntaxKind.EqualsToken
? this.EatTokenAsKind(SyntaxKind.IdentifierToken)
: this.ParseIdentifierToken();

Check failure on line 13914 in src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

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src/Compilers/CSharp/Portable/Parser/LanguageParser.cs#L13914 

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs(13914,1): error IDE0055: (NETCORE_ENGINEERING_TELEMETRY=Build) Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055)

Check failure on line 13914 in src/Compilers/CSharp/Portable/Parser/LanguageParser.cs

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Azure Pipelines / roslyn-CI (Correctness Correctness_Analyzers)

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs#L13914 

src/Compilers/CSharp/Portable/Parser/LanguageParser.cs(13914,1): error IDE0055: (NETCORE_ENGINEERING_TELEMETRY=Build) Fix formatting (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0055)
return _syntaxFactory.LetClause(
this.EatContextualToken(SyntaxKind.LetKeyword),
this.ParseIdentifierToken(),
letKeyword,
identifier,
this.EatToken(SyntaxKind.EqualsToken),
this.ParseExpressionCore());
}
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45 changes: 45 additions & 0 deletions src/Compilers/CSharp/Test/Syntax/Parsing/ExpressionParsingTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7330,5 +7330,50 @@ public void ObjectInitializerWithColonAndDashInsteadOfEqualsSigns()
}
EOF();
}

[Fact, WorkItem("https://github.com/dotnet/roslyn/issues/10446")]
public void LetClauseWithKeywordAsIdentifier()
{
UsingExpression("from m in methods let params = 1 select m",
// (1,23): error CS1041: Identifier expected; 'params' is a keyword
// from m in methods let params = m.GetParameters() select m
Diagnostic(ErrorCode.ERR_IdentifierExpectedKW, "params").WithArguments("", "params").WithLocation(1, 23));

N(SyntaxKind.QueryExpression);
{
N(SyntaxKind.FromClause);
{
N(SyntaxKind.FromKeyword);
N(SyntaxKind.IdentifierToken, "m");
N(SyntaxKind.InKeyword);
N(SyntaxKind.IdentifierName);
{
N(SyntaxKind.IdentifierToken, "methods");
}
}
N(SyntaxKind.QueryBody);
{
N(SyntaxKind.LetClause);
{
N(SyntaxKind.LetKeyword);
M(SyntaxKind.IdentifierToken);
N(SyntaxKind.EqualsToken);
N(SyntaxKind.NumericLiteralExpression);
{
N(SyntaxKind.NumericLiteralToken, "1");
}
}
N(SyntaxKind.SelectClause);
{
N(SyntaxKind.SelectKeyword);
N(SyntaxKind.IdentifierName);
{
N(SyntaxKind.IdentifierToken, "m");
}
}
}
}
EOF();
}
}
}
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