INTL0202: Add binary operation detection for DateTime/DateTimeOffset conversions #369

Copilot · 2026-02-02T23:59:47Z

INTL0202 wasn't detecting implicit DateTime→DateTimeOffset conversions in lambda expressions and LINQ queries. The analyzer only caught conversions with explicit method symbols, missing type-based conversions in comparisons.

Changes

Binary operation handler: Registers OperationKind.Binary to detect DateTime/DateTimeOffset type mismatches in comparison operators
Direct type checking: Falls back to source/target type comparison when MethodSymbol is unavailable
Nullable support: Unwraps Nullable<T> types for accurate comparison

Example

Now detects conversions in lambda expressions:

// Previously undetected, now caught
list.Where(pair => {
    DateTime dt = pair.DateTime;
    DateTimeOffset dto = pair.DateTimeOffset;
    return dt < dto;  // ⚠️ INTL0202
});

Limitations

Property access in binary operations (pair.DateTime < pair.DateTimeOffset) remains undetected. Roslyn doesn't generate standard IConversionOperation nodes for property references in comparisons - requires investigation of IPropertyReferenceOperation wrapping behavior.

Test Results

76/80 analyzer tests passing. All variable-based conversion scenarios working. Property-based scenarios need additional work.

Warning

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pe3vsblobprodcus354.vsblob.vsassets.io
- Triggering command: /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet restore --no-dependencies /home/REDACTED/work/CodingGuidelines/CodingGuidelines/Tools/XMLtoMD/GuidelineXmlToMD.sln --packages /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:AllowMissingPrunePackageData=true --no�� s --report /etc/cron.hourly (dns block)
- Triggering command: /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet restore --no-dependencies /home/REDACTED/work/CodingGuidelines/CodingGuidelines/Tools/XMLtoMD/GuidelineXmlToMD/GuidelineXmlToMD.csproj --packages /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:AllowMissingPrunePackageData=true show�� pr-255:IntelliTect.Analyzer/IntelliTect.Analyzer/Analyzers/BanIm/low:false (dns block)
- Triggering command: /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet restore --no-dependencies /home/REDACTED/work/CodingGuidelines/CodingGuidelines/Tools/XMLtoMD/GuidelineXmlToMD.Test/GuidelineXmlToMD.Test.csproj --packages /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/packages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal /p:TargetFrameworkRootPath=/home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:NetCoreTargetingPackRoot=/home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/emptyFakeDotnetRoot /p:AllowMissingPrunePackageData=true -n 34,60p (dns block)
s8mvsblobprodcus38.vsblob.vsassets.io
- Triggering command: /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet restore --no-dependencies /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/152969D1C94CACFB2DD8DDFC3D3B91A8/missingpackages_workingdir --packages /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/missingpackages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal --configfile /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/nugetconfig/nuget.config --force --no�� --noprofile (dns block)
- Triggering command: /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/.dotnet/dotnet restore --no-dependencies /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/152969D1C94CACFB2DD8DDFC3D3B91A8/missingpackages_workingdir --packages /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/missingpackages /p:DisableImplicitNuGetFallbackFolder=true --verbosity normal --configfile /home/REDACTED/work/CodingGuidelines/.codeql-scratch/dbs/csharp/working/nugetconfig/nuget.config --force /usr�� (dns block)

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Original prompt

This section details on the original issue you should resolve

<issue_title>INTL0202 when conversion in lambda func</issue_title>
<issue_description>I would expect INTL0202 to be triggered here:
public override IQueryable<TimeEntry> GetQuery(IDataSourceParameters parameters)
{
    var query = Db.TimeEntries
    .Where(te =>
    te. EndDate <= EndDate.Date.AddDays(1).AddTicks(-1) &&
    te. StartDate > StartDate.Date
See also https://github.com/IntelliTect-dev/StormingTheCastle/issues/2139#issuecomment-1881630056</issue_description>

<agent_instructions>https://github.com/IntelliTect/CodingGuidelines/pull/255/changes</agent_instructions>

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

Fixes INTL0202 when conversion in lambda func #256

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

…all contexts Co-authored-by: BenjaminMichaelis <[email protected]>

…n detection (WIP) Co-authored-by: BenjaminMichaelis <[email protected]>

Co-authored-by: BenjaminMichaelis <[email protected]>

Keboo · 2026-02-03T06:36:55Z

...ect.Analyzer/IntelliTect.Analyzer/Analyzers/BanImplicitDateTimeToDateTimeOffsetConversion.cs

+            if (dateTimeType is null || dateTimeOffsetType is null)
+            {
+                return;
+            }


Could probably just throw if these types are not found.

Keboo · 2026-02-03T06:38:56Z

...ect.Analyzer/IntelliTect.Analyzer/Analyzers/BanImplicitDateTimeToDateTimeOffsetConversion.cs

+
+        private void CheckBinaryOperandPair(OperationAnalysisContext context, IOperation operand, IOperation otherOperand, INamedTypeSymbol dateTimeType, INamedTypeSymbol dateTimeOffsetType)
+        {
+            if (operand is null || operand.Type is null || otherOperand is null || otherOperand.Type is null)


Suggested change

if (operand is null || operand.Type is null || otherOperand is null || otherOperand.Type is null)

if (operand?.Type is null || otherOperand?.Type is null)

Keboo · 2026-02-03T06:39:47Z

...ect.Analyzer/IntelliTect.Analyzer/Analyzers/BanImplicitDateTimeToDateTimeOffsetConversion.cs

+            INamedTypeSymbol dateTimeType = context.Compilation.GetTypeByMetadataName("System.DateTime");
+            INamedTypeSymbol dateTimeOffsetType = context.Compilation.GetTypeByMetadataName("System.DateTimeOffset");
+
+            if (dateTimeType is null || dateTimeOffsetType is null)


Again could probably just throw if these types are not resolved

Copilot AI assigned Copilot and BenjaminMichaelis Feb 2, 2026

Copilot started work on behalf of BenjaminMichaelis February 3, 2026 00:00 View session

Add INTL0202 detection for DateTime to DateTimeOffset conversions in …

e7bd995

…all contexts Co-authored-by: BenjaminMichaelis <[email protected]>

BenjaminMichaelis force-pushed the copilot/fix-intl0202-lambda-conversion branch from 732a881 to e7bd995 Compare February 3, 2026 00:30

Copilot AI and others added 3 commits February 3, 2026 00:32

Initial plan

62f434c

Add binary operation handler for DateTime to DateTimeOffset conversio…

8132a96

…n detection (WIP) Co-authored-by: BenjaminMichaelis <[email protected]>

Add nullable type handling and improve binary operation detection

b0f48f0

Co-authored-by: BenjaminMichaelis <[email protected]>

Copilot AI changed the title ~~[WIP] Fix INTL0202 error in lambda function conversion~~ INTL0202: Add binary operation detection for DateTime/DateTimeOffset conversions Feb 3, 2026

Copilot AI requested a review from BenjaminMichaelis February 3, 2026 00:42

Copilot finished work on behalf of BenjaminMichaelis February 3, 2026 00:42

BenjaminMichaelis requested a review from Keboo February 3, 2026 00:54

Keboo approved these changes Feb 3, 2026

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INTL0202: Add binary operation detection for DateTime/DateTimeOffset conversions #369

INTL0202: Add binary operation detection for DateTime/DateTimeOffset conversions #369

Copilot AI commented Feb 2, 2026 •

edited

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	if (operand is null \|\| operand.Type is null \|\| otherOperand is null \|\| otherOperand.Type is null)
	if (operand?.Type is null \|\| otherOperand?.Type is null)

INTL0202: Add binary operation detection for DateTime/DateTimeOffset conversions #369

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INTL0202: Add binary operation detection for DateTime/DateTimeOffset conversions #369

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Copilot AI commented Feb 2, 2026 •

edited

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