Fix trimming analyzer missing diagnostics for method calls in field access expressions

[Copilot]

Fix for Type.GetInterfaceMap Trimming Analyzer Issue (#117849)

Problem

The trimming analyzer fails to report diagnostics when method calls are used in field access expressions. For example, type.GetInterfaceMap(@interface).TargetMethods does not warn, while type.GetInterfaceMap(@interface) correctly reports IL2072.

Root cause: TrimAnalysisVisitor.VisitFieldReference does not visit the field's instance operation before processing the field itself.

Fix: Visit the instance before processing the field, consistent with how other visitor methods handle instances (property references, event references).

Changes

1. TrimAnalysisVisitor.cs: Added Visit(fieldRef.Instance, state); at the start of VisitFieldReference()
2. GetInterfaceDataFlow.cs: Added comprehensive test cases for the GetInterfaceMap scenario
   • Fixed to use typeof(TestType) instead of o.GetType() to avoid unrelated IL2075 warnings
   • Uses array indexing [0] instead of LINQ for test framework compatibility

Testing

• ✅ Code review - no issues
• ✅ Security scan (CodeQL) - no vulnerabilities
• ✅ Test compilation - successful
• ✅ Test warnings - focused on IL2072 only, no unexpected IL2075 warnings
• ⏳ Full test suite - will be verified in CI

Impact

This is a targeted fix that only affects field reference analysis. The change ensures that:

1. Method calls are analyzed regardless of how their return values are used
2. Behavior is consistent across all usage patterns
3. No false negatives in trimming diagnostics

Original prompt

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This section details on the original issue you should resolve

<issue_title>Type.GetInterfaceMap(Type) is treated oddly by the trimming analyzers</issue_title>
<issue_description>### Description

The second usage of GetInterfaceMap causes

IL2072: 'interfaceType' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicMethods', 'DynamicallyAccessedMemberTypes.NonPublicMethods' in call to 'System.Type.GetInterfaceMap(Type)'. The return value of method 'System.Linq.Enumerable.First<TSource>(IEnumerable<TSource>)' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.

while the first usage doesn't cause any warning.

I am not sure whether it's how it's supposed to be or it's an actual bug.

Reproduction Steps

object o = new();

var type = o.GetType();

var @interface = type.GetInterfaces().First();

_ = type.GetInterfaceMap(@interface).TargetMethods;

_ = type.GetInterfaceMap(@interface);

Expected behavior

I am not sure

Actual behavior

The warning is reported or not depending on whether some field is referenced or not

Regression?

No response

Known Workarounds

No response

Configuration

.NET 8

Other information

No response</issue_description>

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

• Fixes Type.GetInterfaceMap(Type) is treated oddly by the trimming analyzers #108114

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[sbomer]

@copilot fix error:

'/__w/1/s/src/tools/illink/test/Mono.Linker.Tests.Cases.Expectations/Support/DynamicallyAccessedMembersAttribute.cs'.\n/__w/1/s/artifacts/bin/ILLink.testcases/linker_tests/DataFlow/GetInterfaceDataFlow/GetInterfaceDataFlow.cs(197,55): error CS1061: 'Type[]' does not contain a definition for 'First' and no accessible extension method 'First' accepting a first argument of type 'Type[]' could be found (are you missing a using directive or an assembly reference?)\n/__w/1/s/artifacts/bin/ILLink.testcases/linker_tests/DataFlow/GetInterfaceDataFlow/GetInterfaceDataFlow.cs(209,55): error CS1061: 'Type[]' does not contain a definition for 'First' and no accessible extension method 'First' accepting a first argument of type 'Type[]' could be found (are you missing a using directive or an assembly reference?)\n/__w/1/s/artifacts/bin/ILLink.testcases/linker_tests/DataFlow/GetInterfaceDataFlow/GetInterfaceDataFlow.cs(219,55): error CS1061: 'Type[]' does not contain a definition for 'First' and no accessible extension method 'First' accepting a first argument of type 'Type[]' could be found (are you missing a using directive or an assembly reference?)\n)\n---- System.Exception : Roslyn compilation

[Copilot]

@copilot fix error:

'/__w/1/s/src/tools/illink/test/Mono.Linker.Tests.Cases.Expectations/Support/DynamicallyAccessedMembersAttribute.cs'.\n/__w/1/s/artifacts/bin/ILLink.testcases/linker_tests/DataF...

Fixed in 8b353ad. Replaced .First() with [0] array indexing since the test framework doesn't include LINQ assembly references. This pattern is consistent with other dataflow tests (e.g., ArrayDataFlow.cs).

[sbomer]

@copilot fix this error:

Unexpected warning found: ILLink: Trim analysis warning IL2075: Mono.Linker.Tests.Cases.DataFlow.GetInterfaceDataFlow.GetInterfaceMap_DataFlow.TestDirectCall(): 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.Interfaces' in call to 'System.Type.GetInterfaces()'. The return value of method 'System.Object.GetType()' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.
Unexpected warning found: ILLink: Trim analysis warning IL2075: Mono.Linker.Tests.Cases.DataFlow.GetInterfaceDataFlow.GetInterfaceMap_DataFlow.TestFieldAccess(): 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.Interfaces' in call to 'System.Type.GetInterfaces()'. The return value of method 'System.Object.GetType()' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.
Unexpected warning found: ILLink: Trim analysis warning IL2075: Mono.Linker.Tests.Cases.DataFlow.GetInterfaceDataFlow.GetInterfaceMap_DataFlow.TestMultipleFieldAccess(): 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.Interfaces' in call to 'System.Type.GetInterfaces()'. The return value of method 'System.Object.GetType()' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.

Be sure to run this test before committing.

[Copilot]

@copilot fix this error:

Unexpected warning found: ILLink: Trim analysis warning IL2075: Mono.Linker.Tests.Cases.DataFlow.GetInterfaceDataFlow.GetInterfaceMap_DataFlow.TestDirectCall(): 'this' argu...

Fixed in 025264e. Replaced o.GetType() with typeof(TestType) to avoid the unrelated IL2075 warnings. The tests now focus only on the IL2072 warnings for GetInterfaceMap, which is what we're testing with this fix.

[Copilot]

Pull request overview

This PR fixes a trimming analyzer bug where diagnostics were not reported when method calls appear in field access expressions. For example, type.GetInterfaceMap(@interface).TargetMethods was not warning even though @interface lacks required annotations, while type.GetInterfaceMap(@interface) correctly reports IL2072.

Changes:

• Added instance visiting in VisitFieldReference to ensure method calls in field access chains are analyzed
• Updated field assignment handling to explicitly visit instances before processing field values
• Added comprehensive test coverage for the GetInterfaceMap scenario with field access patterns

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
TrimAnalysisVisitor.cs	Added Visit(fieldRef.Instance, state) in VisitFieldReference to analyze method calls used as field instances, matching the pattern used by property and event references
LocalDataFlowVisitor.cs	Refactored assignment handling to explicitly visit field reference instances, ensuring consistency for both read and write operations
GetInterfaceDataFlow.cs	Added test class GetInterfaceMap_DataFlow with comprehensive test cases covering direct calls, field access, multiple field access, and properly annotated scenarios
FieldDataFlow.cs	Updated test expectations in AccessReturnedInstanceField to expect IL2072 warnings for all tools (removed tool-specific exclusions)