Make all fragment shader out variables require location layout qualifier

src/compiler/translator/ValidateOutputs.cpp

@@ -14,7 +14,7 @@ ValidateOutputs::ValidateOutputs(TInfoSinkBase& sink, int maxDrawBuffers)
       mSink(sink),
       mMaxDrawBuffers(maxDrawBuffers),
       mNumErrors(0),
-      mHasUnspecifiedOutputLocation(false)
+      mUnspecifiedOutputLocationCount(0)
 {
 }
 
@@ -32,14 +32,15 @@ void ValidateOutputs::visitSymbol(TIntermSymbol *symbol)
     {
         const TType &type = symbol->getType();
         const int location = type.getLayoutQualifier().location;
+        const bool isUnspecifiedOutputLocation = location == -1;
 
-        if (mHasUnspecifiedOutputLocation)
+        if (mUnspecifiedOutputLocationCount > 0 || (isUnspecifiedOutputLocation && !mOutputMap.empty()))
         {
             error(symbol->getLine(), "must explicitly specify all locations when using multiple fragment outputs", name.c_str());
         }
-        else if (location == -1)
+        else if (isUnspecifiedOutputLocation)
         {
-            mHasUnspecifiedOutputLocation = true;
+            ++mUnspecifiedOutputLocationCount;
         }
         else
         {

src/compiler/translator/ValidateOutputs.h

@@ -26,7 +26,7 @@ class ValidateOutputs : public TIntermTraverser
     TInfoSinkBase& mSink;
     int mMaxDrawBuffers;
     int mNumErrors;
-    bool mHasUnspecifiedOutputLocation;
+    bool mUnspecifiedOutputLocationCount;
 
     typedef std::map<int, TIntermSymbol*> OutputMap;
     OutputMap mOutputMap;

src/tests/compiler_tests/MalformedShader_test.cpp

@@ -689,6 +689,64 @@ TEST_F(MalformedShaderTest, LayoutQualifierInFunctionReturnType)
     }
 }
 
+// If there is more than one output, the location must be specified for all outputs.
+// (ESSL 3.00.04 section 4.3.8.2)
+TEST_F(MalformedShaderTest, TwoOutputsNoLayoutQualifiers)
+{
+    const std::string &shaderString =
+        "#version 300 es\n"
+        "precision mediump float;\n"
+        "uniform vec4 u;\n"
+        "out vec4 my_FragColor;\n"
+        "out vec4 my_SecondaryFragColor;\n"
+        "void main() {\n"
+        "    my_FragColor = vec4(1.0);\n"
+        "    my_SecondaryFragColor = vec4(0.5);\n"
+        "}\n";
+    if (compile(shaderString))
+    {
+        FAIL() << "Shader compilation succeeded, expecting failure " << mInfoLog;
+    }
+}
+
+// (ESSL 3.00.04 section 4.3.8.2)
+TEST_F(MalformedShaderTest, TwoOutputsFirstLayoutQualifier)
+{
+    const std::string &shaderString =
+        "#version 300 es\n"
+        "precision mediump float;\n"
+        "uniform vec4 u;\n"
+        "layout(location = 0) out vec4 my_FragColor;\n"
+        "out vec4 my_SecondaryFragColor;\n"
+        "void main() {\n"
+        "    my_FragColor = vec4(1.0);\n"
+        "    my_SecondaryFragColor = vec4(0.5);\n"
+        "}\n";
+    if (compile(shaderString))
+    {
+        FAIL() << "Shader compilation succeeded, expecting failure " << mInfoLog;
+    }
+}
+
+// (ESSL 3.00.04 section 4.3.8.2)
+TEST_F(MalformedShaderTest, TwoOutputsSecondLayoutQualifier)
+{
+    const std::string &shaderString =
+        "#version 300 es\n"
+        "precision mediump float;\n"
+        "uniform vec4 u;\n"
+        "out vec4 my_FragColor;\n"
+        "layout(location = 0) out vec4 my_SecondaryFragColor;\n"
+        "void main() {\n"
+        "    my_FragColor = vec4(1.0);\n"
+        "    my_SecondaryFragColor = vec4(0.5);\n"
+        "}\n";
+    if (compile(shaderString))
+    {
+        FAIL() << "Shader compilation succeeded, expecting failure " << mInfoLog;
+    }
+}
+
 // Uniforms can be arrays (ESSL 3.00 section 4.3.5)
 TEST_F(MalformedShaderTest, UniformArray)
 {