Fix issue with getUniformFloat crashing with hot reload (#180138)

Fixes https://github.com/flutter/flutter/issues/180101.

Our hot reloading behavior for shader uniforms only handled the case
where uniforms were reordered. In the case that a uniform was renamed or
deleted, and a user had acquired a handle to that uniform via
`getUniformFloat`, we would try (and fail) to locate that uniform in the
shader, and the program would crash.

This PR fixes that issue and adds a test to verify. Also manually
verified on mac and android

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above.
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[test-exempt].
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Fixes] where supported.
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engine/src/flutter/lib/ui/fixtures/shaders/general_shaders/BUILD.gn

@@ -26,6 +26,7 @@ if (enable_unittests) {
     "uniforms_reordered.frag",
     "uniforms_sorted.frag",
     "uniforms.frag",
+    "uniforms_renamed.frag",
     "vec3_uniform.frag",
   ]
 

engine/src/flutter/lib/ui/fixtures/shaders/general_shaders/uniforms_renamed.frag

@@ -0,0 +1,20 @@
+#version 320 es
+
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Note: Don't update this file without updating `uniforms_reordered.frag`.
+// Note: Don't update this file without updating `uniforms_inserted.frag`.
+
+precision highp float;
+
+layout(location = 0) out vec4 oColor;
+
+layout(location = 0) uniform float iFloatUniformRenamed;
+layout(location = 1) uniform vec2 iVec2Uniform;
+layout(location = 2) uniform mat2 iMat2Uniform;
+
+void main() {
+  oColor = vec4(iFloatUniformRenamed, iVec2Uniform, iMat2Uniform[1][1]);
+}

engine/src/flutter/lib/ui/painting.dart

@@ -5391,6 +5391,10 @@ base class FragmentProgram extends NativeFieldWrapperClass1 {
           return true;
         }
 
+        if (!program._hasUniform(slot.name)) {
+          return true;
+        }
+
         slot._shaderIndex = program._getUniformFloatIndex(slot.name, slot.index);
         return false;
       });
@@ -5409,6 +5413,10 @@ base class FragmentProgram extends NativeFieldWrapperClass1 {
     });
   }
 
+  bool _hasUniform(String name) {
+    return _uniformInfo.any((dynamic entry) => (entry! as Map<String, Object>)['name'] == name);
+  }
+
   int _getImageSamplerIndex(String name) {
     var index = 0;
     var found = false;

engine/src/flutter/testing/dart/vm_service/shader_reload_test.dart

@@ -130,6 +130,43 @@ void main() {
     }
   });
 
+  test('rename uniforms', () async {
+    if (impellerEnabled) {
+      // Needs https://github.com/flutter/flutter/issues/129659
+      return;
+    }
+    final testAssetName = 'test_rename_uniforms_${DateTime.now().millisecondsSinceEpoch}.frag.iplr';
+    final String buildDir = Platform.environment['FLUTTER_BUILD_DIRECTORY']!;
+    final String assetsDir = path.join(buildDir, 'gen/flutter/lib/ui/assets');
+    final String shaderSrcA = path.join(assetsDir, 'uniforms.frag.iplr');
+    final String shaderSrcB = path.join(assetsDir, 'uniforms_renamed.frag.iplr');
+    final String shaderSrcC = path.join(assetsDir, testAssetName);
+
+    final fileC = File(shaderSrcC);
+    final Uint8List sourceA = File(shaderSrcA).readAsBytesSync();
+    final Uint8List sourceB = File(shaderSrcB).readAsBytesSync();
+
+    fileC.writeAsBytesSync(sourceA, flush: true);
+
+    try {
+      final FragmentProgram program = await FragmentProgram.fromAsset(testAssetName);
+      final FragmentShader shader = program.fragmentShader();
+      final UniformFloatSlot slotA = shader.getUniformFloat('iFloatUniform');
+      slotA.set(1.0);
+
+      fileC.writeAsBytesSync(sourceB, flush: true);
+      await _performReload(testAssetName);
+
+      final UniformFloatSlot slotB = shader.getUniformFloat('iFloatUniformRenamed');
+      // Make sure this doesn't break.
+      slotB.set(0.0);
+    } finally {
+      if (fileC.existsSync()) {
+        fileC.deleteSync();
+      }
+    }
+  });
+
   test('reorder samplers', () async {
     if (impellerEnabled) {
       // Needs https://github.com/flutter/flutter/issues/129659