Add MA0184: Report interpolated strings without parameters by Copilot · Pull Request #984 · meziantou/Meziantou.Analyzer

Copilot · 2026-02-01T20:10:30Z

Original prompt

This section details on the original issue you should resolve

<issue_title>Report diagnostic for interpolated string without any parameter</issue_title>
<issue_description>As far as I can tell, there's no analyzer that reports a diagnostic when you needlessly define a string as interpolated string.
var x = $"Required attribute 'output' not found."; // NOK
var y = "Required attribute 'output' not found."; // OK

I know this does not have any runtime impact (unless if you needless use `String.Create(...)`), so I can understand if you don't want to waste time with this.</issue_description>

<agent_instructions>Make sure the rule should be disabled by default, and a suggestion.
Only report when the value is a string, not a FormattableString and a custom Handler (InterpolatedStringHandler)</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

Fixes Report diagnostic for interpolated string without any parameter #981

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…ters Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

meziantou · 2026-02-01T20:30:48Z

@@ -0,0 +1,257 @@
+using Meziantou.Analyzer.Rules;


@copilot Can you add test with raw strings

_ = [|$""" Sample """|];

Added test for raw interpolated strings in commit ada289b. The fixer now properly handles both regular and raw interpolated strings by preserving the raw string format when removing the $ prefix.

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

meziantou · 2026-02-01T20:54:13Z

@copilot On older version of Roslyn 3.8, 4.2, the following test fails:

Failed Meziantou.Analyzer.Test.Rules.DoNotUseInterpolatedStringWithoutParametersAnalyzerTests.RawInterpolatedStringWithoutParameters_ShouldReportDiagnostic [53 ms]
  Error Message:
   The code doesn't compile.

class TypeName
{
    public void Test()
    {
        _ = $"""
               ^ CS1002: ; expected
               ^ CS1010: Newline in constant
                ^ CS1002: ; expected
            Sample
            ^^^^^^ CS0103: The name 'Sample' does not exist in the current context
                  ^ CS1002: ; expected
            """;
              ^^ CS1002: ; expected
              ^ CS1010: Newline in constant
                ^ CS1002: ; expected
    }
}

meziantou · 2026-02-01T20:54:42Z

@copilot The documentation is no up to date. Can you regenerate it?

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Copilot · 2026-02-01T20:58:36Z

@copilot On older version of Roslyn 3.8, 4.2, the following test fails:

...

Fixed in commit 18b5049. The raw interpolated string test is now wrapped with #if CSHARP11_OR_GREATER and specifies C# 11 language version to ensure it only runs on Roslyn versions that support raw string literals.

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Copilot · 2026-02-01T21:00:54Z

@copilot The documentation is no up to date. Can you regenerate it?

Documentation regenerated in commit 872fa23. Added source links and fixed formatting.

meziantou · 2026-02-01T21:06:02Z

@copilot

[xUnit.net 00:00:35.15]     Meziantou.Analyzer.Test.Rules.DoNotUseInterpolatedStringWithoutParametersAnalyzerTests.InterpolatedStringWithoutParameters_CustomInterpolatedStringHandler_ShouldNotReportDiagnostic [FAIL]
[xUnit.net 00:00:35.16]       The code doesn't compile.
[xUnit.net 00:00:35.16]       
[xUnit.net 00:00:35.16]       class TypeName
[xUnit.net 00:00:35.16]       {
[xUnit.net 00:00:35.16]           public void Test(CustomInterpolatedStringHandler handler)
[xUnit.net 00:00:35.16]           {
[xUnit.net 00:00:35.16]           }
[xUnit.net 00:00:35.16]       
[xUnit.net 00:00:35.16]           public void Run()
[xUnit.net 00:00:35.16]           {
[xUnit.net 00:00:35.16]               Test($"Required attribute 'output' not found.");
[xUnit.net 00:00:35.16]                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ CS1503: Argument 1: cannot convert from 'string' to 'CustomInterpolatedStringHandler'
[xUnit.net 00:00:35.16]           }
[xUnit.net 00:00:35.16]       }
[xUnit.net 00:00:35.16]       
[xUnit.net 00:00:35.16]       [System.Runtime.CompilerServices.InterpolatedStringHandler]
[xUnit.net 00:00:35.16]       public struct CustomInterpolatedStringHandler
[xUnit.net 00:00:35.16]       {
[xUnit.net 00:00:35.16]           public CustomInterpolatedStringHandler(int literalLength, int formattedCount)
[xUnit.net 00:00:35.16]           {
[xUnit.net 00:00:35.16]           }
[xUnit.net 00:00:35.16]       
[xUnit.net 00:00:35.16]           public void AppendLiteral(string s)
[xUnit.net 00:00:35.16]           {
[xUnit.net 00:00:35.16]           }
[xUnit.net 00:00:35.16]       }
[xUnit.net 00:00:35.16]       Stack Trace:
[xUnit.net 00:00:35.16]         /_/tests/Meziantou.Analyzer.Test/Helpers/ProjectBuilder.Validation.cs(310,0): at TestHelper.ProjectBuilder.GetSortedDiagnosticsFromDocuments(IList`1 analyzers, Document[] documents, Boolean compileSolution)
[xUnit.net 00:00:35.16]         /_/tests/Meziantou.Analyzer.Test/Helpers/ProjectBuilder.Validation.cs(142,0): at TestHelper.ProjectBuilder.GetSortedDiagnostics(IList`1 analyzers)
[xUnit.net 00:00:35.16]         /_/tests/Meziantou.Analyzer.Test/Helpers/ProjectBuilder.Validation.cs(52,0): at TestHelper.ProjectBuilder.VerifyDiagnostics(IList`1 analyzers, IList`1 expected)
[xUnit.net 00:00:35.16]         /_/tests/Meziantou.Analyzer.Test/Helpers/ProjectBuilder.Validation.cs(35,0): at TestHelper.ProjectBuilder.ValidateAsync()
[xUnit.net 00:00:35.16]         /_/tests/Meziantou.Analyzer.Test/Rules/DoNotUseInterpolatedStringWithoutParametersAnalyzerTests.cs(138,0): at Meziantou.Analyzer.Test.Rules.DoNotUseInterpolatedStringWithoutParametersAnalyzerTests.InterpolatedStringWithoutParameters_CustomInterpolatedStringHandler_ShouldNotReportDiagnostic()
[xUnit.net 00:00:35.16]         --- End of stack trace from previous location ---
  Failed Meziantou.Analyzer.Test.Rules.DoNotUseInterpolatedStringWithoutParametersAnalyzerTests.InterpolatedStringWithoutParameters_CustomInterpolatedStringHandler_ShouldNotReportDiagnostic [89 ms]
  Error Message:
   The code doesn't compile.

class TypeName
{
    public void Test(CustomInterpolatedStringHandler handler)
    {
    }

    public void Run()
    {
        Test($"Required attribute 'output' not found.");
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ CS1503: Argument 1: cannot convert from 'string' to 'CustomInterpolatedStringHandler'
    }
}

[System.Runtime.CompilerServices.InterpolatedStringHandler]
public struct CustomInterpolatedStringHandler
{
    public CustomInterpolatedStringHandler(int literalLength, int formattedCount)
    {
    }

    public void AppendLiteral(string s)
    {
    }
}
  Stack Trace:
     at TestHelper.ProjectBuilder.GetSortedDiagnosticsFromDocuments(IList`1 analyzers, Document[] documents, Boolean compileSolution) in /_/tests/Meziantou.Analyzer.Test/Helpers/ProjectBuilder.Validation.cs:line 310
   at TestHelper.ProjectBuilder.GetSortedDiagnostics(IList`1 analyzers) in /_/tests/Meziantou.Analyzer.Test/Helpers/ProjectBuilder.Validation.cs:line 142
   at TestHelper.ProjectBuilder.VerifyDiagnostics(IList`1 analyzers, IList`1 expected) in /_/tests/Meziantou.Analyzer.Test/Helpers/ProjectBuilder.Validation.cs:line 52
   at TestHelper.ProjectBuilder.ValidateAsync() in /_/tests/Meziantou.Analyzer.Test/Helpers/ProjectBuilder.Validation.cs:line 35
   at Meziantou.Analyzer.Test.Rules.DoNotUseInterpolatedStringWithoutParametersAnalyzerTests.InterpolatedStringWithoutParameters_CustomInterpolatedStringHandler_ShouldNotReportDiagnostic() in /_/tests/Meziantou.Analyzer.Test/Rules/DoNotUseInterpolatedStringWithoutParametersAnalyzerTests.cs:line 138
--- End of stack trace from previous location ---

Error: The code doesn't compile.

class TypeName
{
    public void Test(CustomInterpolatedStringHandler handler)
    {
    }

    public void Run()
    {
        Test($"Required attribute 'output' not found.");
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ CS1503: Argument 1: cannot convert from 'string' to 'CustomInterpolatedStringHandler'
    }
}

[System.Runtime.CompilerServices.InterpolatedStringHandler]
public struct CustomInterpolatedStringHandler
{
    public CustomInterpolatedStringHandler(int literalLength, int formattedCount)
    {
    }

    public void AppendLiteral(string s)
    {
    }
}

…th CSHARP10_OR_GREATER Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Copilot · 2026-02-01T21:10:36Z

@copilot

...

Fixed in commit c53d96e. The CustomInterpolatedStringHandler test is now wrapped with #if CSHARP10_OR_GREATER to ensure it only runs on Roslyn versions that support the InterpolatedStringHandlerAttribute (C# 10 / .NET 6+).

Initial plan

bfaf9d5

Copilot AI assigned Copilot and meziantou Feb 1, 2026

Copilot started work on behalf of meziantou February 1, 2026 20:10 View session

Copilot AI and others added 3 commits February 1, 2026 20:18

Add MA0184 analyzer and fixer for interpolated strings without parame…

2f3bd38

…ters Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Update documentation for MA0184

241d985

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Address code review feedback - use attribute check and add documentation

2894b3d

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Add diagnostic for interpolated string without parameters~~ Add MA0184: Report interpolated strings without parameters Feb 1, 2026

Copilot AI requested a review from meziantou February 1, 2026 20:26

Copilot finished work on behalf of meziantou February 1, 2026 20:26

meziantou reviewed Feb 1, 2026

View reviewed changes

Copilot started work on behalf of meziantou February 1, 2026 20:31 View session

Add test for raw interpolated strings and improve fixer

ada289b

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Copilot AI requested a review from meziantou February 1, 2026 20:38

Copilot finished work on behalf of meziantou February 1, 2026 20:38

Copilot started work on behalf of meziantou February 1, 2026 20:54 View session

Fix raw string test for older Roslyn versions with CSHARP11_OR_GREATER

18b5049

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Copilot finished work on behalf of meziantou February 1, 2026 20:59

Copilot started work on behalf of meziantou February 1, 2026 20:59 View session

Regenerate documentation with source links

872fa23

Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Copilot finished work on behalf of meziantou February 1, 2026 21:01

Copilot started work on behalf of meziantou February 1, 2026 21:06 View session

Fix CustomInterpolatedStringHandler test for older Roslyn versions wi…

c53d96e

…th CSHARP10_OR_GREATER Co-authored-by: meziantou <509220+meziantou@users.noreply.github.com>

Copilot finished work on behalf of meziantou February 1, 2026 21:11

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Add MA0184: Report interpolated strings without parameters#984

Add MA0184: Report interpolated strings without parameters#984
meziantou merged 8 commits into
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