Always write to gl_Position when compiling shaders with

src/compiler/translator/Compiler.cpp

@@ -322,7 +322,10 @@ TIntermNode *TCompiler::compileTreeImpl(const char *const shaderStrings[],
         if (success && (compileOptions & SH_CLAMP_INDIRECT_ARRAY_BOUNDS))
             arrayBoundsClamper.MarkIndirectArrayBoundsForClamping(root);
 
-        if (success && shaderType == GL_VERTEX_SHADER && (compileOptions & SH_INIT_GL_POSITION))
+        // gl_Position is always written in compatibility output mode
+        if (success && shaderType == GL_VERTEX_SHADER &&
+            ((compileOptions & SH_INIT_GL_POSITION) ||
+             (outputType == SH_GLSL_COMPATIBILITY_OUTPUT)))
             initializeGLPosition(root);
 
         // This pass might emit short circuits so keep it before the short circuit unfolding

src/tests/angle_unittests.gypi

@@ -47,6 +47,7 @@
             '<(angle_path)/src/tests/compiler_tests/ExpressionLimit_test.cpp',
             '<(angle_path)/src/tests/compiler_tests/EXT_blend_func_extended_test.cpp',
             '<(angle_path)/src/tests/compiler_tests/FragDepth_test.cpp',
+            '<(angle_path)/src/tests/compiler_tests/GLSLCompatibilityOutput_test.cpp',
             '<(angle_path)/src/tests/compiler_tests/IntermNode_test.cpp',
             '<(angle_path)/src/tests/compiler_tests/MalformedShader_test.cpp',
             '<(angle_path)/src/tests/compiler_tests/NV_draw_buffers_test.cpp',

src/tests/compiler_tests/GLSLCompatibilityOutput_test.cpp

+//
+// Copyright (c) 2016 The ANGLE Project Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// GLSLCompatibilityOutputTest.cpp
+//   Test compiler output for glsl compatibility mode
+//
+
+#include "angle_gl.h"
+#include "gtest/gtest.h"
+#include "GLSLANG/ShaderLang.h"
+#include "tests/test_utils/compiler_test.h"
+
+class GLSLCompatibilityOutputTest : public testing::Test
+{
+  public:
+    GLSLCompatibilityOutputTest() {}
+
+  protected:
+    void compile(const std::string &shaderString)
+    {
+        int compilationFlags = SH_VARIABLES;
+
+        std::string infoLog;
+        bool compilationSuccess =
+            compileTestShader(GL_VERTEX_SHADER, SH_GLES2_SPEC, SH_GLSL_COMPATIBILITY_OUTPUT,
+                              shaderString, compilationFlags, &mTranslatedSource, &infoLog);
+        if (!compilationSuccess)
+        {
+            FAIL() << "Shader compilation failed " << infoLog;
+        }
+    }
+
+    bool find(const char *name) const { return mTranslatedSource.find(name) != std::string::npos; }
+
+  private:
+    std::string mTranslatedSource;
+};
+
+// Verify gl_Position is written when compiling in compatibility mode
+TEST_F(GLSLCompatibilityOutputTest, GLPositionWrittenTest)
+{
+    const std::string &shaderString =
+        "precision mediump float;\n"
+        "void main() {\n"
+        "}";
+    compile(shaderString);
+    EXPECT_TRUE(find("gl_Position"));
+}
\ No newline at end of file