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

[Copilot]

Description

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).

// Before: method calls as field instances were never analyzed
_ = type.GetInterfaceMap(@interface).TargetMethods;  // Silent
_ = type.GetInterfaceMap(@interface);                // IL2072 ✓

// After: both correctly report IL2072

Customer Impact

Silent trimming failures. Code that should warn about missing annotations passes analysis when the return value is immediately used for field access, leading to runtime failures in trimmed applications.

Regression

No. This is a long-standing analyzer gap, not a recent regression.

Testing

• Added regression tests in GetInterfaceDataFlow.cs covering direct calls, field access, and nested field access
• Existing dataflow tests verify no unintended behavioral changes

Risk

Low. The change is minimal (4 lines) and aligns with established patterns in the codebase. It only affects diagnostic reporting—no changes to trimming behavior or false positives. The fix makes the analyzer more correct by eliminating false negatives.

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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