[fix-finder] Remove redundant null-forgiving operator in MamJsonParser.ReadClassRewrites

[github-actions]

Problem

MamJsonParser.ReadClassRewrites uses the ! null-forgiving operator on a value that is already proven non-null by an explicit if (classRewrite == null) continue; guard immediately above it. The dotnet/android coding rules state the ! null-forgiving operator must never be used in C# code; here it is also redundant. The sibling method ReadGlobalMethodCalls performs the exact same call without the operator, confirming it is unnecessary.

Location

• File(s): src/Xamarin.Android.Build.Tasks/Utilities/MamJsonParser.cs
• Line(s): ~73 (inside ReadClassRewrites)

Current Code

foreach (var classRewrite in classRewrites.AsArray ()) {
    if (classRewrite == null) {
        continue;
    }
    if (!TryReadClassFromTo (classRewrite!, out var from, out var to)) {
        Logger (TraceLevel.Verbose, $"No from or to! {classRewrite}");
        continue;
    }

For comparison, ReadGlobalMethodCalls (~line 183) makes the identical call with no !:

if (!TryReadClassFromTo (globalMethodCall, out var from, out var to)) {

Suggested Fix

Remove the ! operator. After the if (classRewrite == null) continue; guard, the C# compiler already narrows classRewrite to non-null, so the operator is redundant:

    if (!TryReadClassFromTo (classRewrite, out var from, out var to)) {

Guidelines

• Repo rule: NEVER use the ! null-forgiving operator in C# code.
• The owning project (Xamarin.Android.Build.Tasks.csproj, netstandard2.0) builds with <Nullable>enable</Nullable> and <WarningsAsErrors>Nullable</WarningsAsErrors>. The identical operator-free call in ReadGlobalMethodCalls already compiles cleanly, so this change will not introduce a nullable warning. The file is also compiled standalone by tools/remap-mam-json-to-xml.
• C# tabs, Mono style; keep the diff minimal.
• Out of scope: the separate JsonNode.Parse ("{}")! on ~line 63 in ReadJson is a genuine (non-redundant) non-null assertion guarding a nullable return value; do not modify it as part of this issue.

Acceptance Criteria

• The ! operator is removed from the TryReadClassFromTo (classRewrite!, ...) call in ReadClassRewrites (becomes classRewrite).
• No other lines are changed.
• All tests pass.
• No new warnings introduced.

Fix-finder metadata

• Script: 02-null-forgiving-operator
• Score: 29/30 (actionability: 10, safety: 9, scope: 10)

Generated by Nightly Fix Finder for issue #11769 · 384 AIC · ⌖ 48.1 AIC · ⊞ 40.8K · ◷

• expires on Jul 4, 2026, 3:38 PM UTC