Make ignorewarnings optional in optimize

This allows targets to opt-in to running R8 without the -ignorewarnings
flag. Ignored warnings can cause code to be optimized incorrectly, so
this makes the build safer for such targets.

Ideally ignore_warnings should default to false, but all targets need to
be fixed for that to happen. As a first step, provide a mechanism for
individual targets to ensure they do not introduce regressions.

Bug: 229727645
Bug: 180878971
Bug: 226127213
Bug: 239990030
Test: m (runs dex_test)
Change-Id: Ic0eef29598c1ee47e958da8a5048d9696165a235
(cherry picked from commit bdad314f97)
Merged-In: Ic0eef29598c1ee47e958da8a5048d9696165a235

java/dex.go

@@ -42,6 +42,9 @@ type DexProperties struct {
 		// True if the module containing this has it set by default.
 		EnabledByDefault bool `blueprint:"mutated"`
 
+		// Whether to continue building even if warnings are emitted.  Defaults to true.
+		Ignore_warnings *bool
+
 		// If true, runs R8 in Proguard compatibility mode (default).
 		// Otherwise, runs R8 in full mode.
 		Proguard_compatibility *bool
@@ -293,7 +296,10 @@ func (d *dexer) r8Flags(ctx android.ModuleContext, flags javaBuilderFlags) (r8Fl
 	}
 
 	// TODO(b/180878971): missing classes should be added to the relevant builds.
-	r8Flags = append(r8Flags, "-ignorewarnings")
+	// TODO(b/229727645): do not use true as default for Android platform builds.
+	if proptools.BoolDefault(opt.Ignore_warnings, true) {
+		r8Flags = append(r8Flags, "-ignorewarnings")
+	}
 
 	return r8Flags, r8Deps
 }