Metal: Fix rewritten out variables with underscores

Fix compilation in case of output variables start with underscores.
Make name emission always emit MSL name ANGLE_{name}, so that GLSL `_e`
and `e` cannot clash. This regressed in angleproject:8558.

Bug: chromium:335744344
Change-Id: Ibae4dba4a24888acc1461582e69d48218ba11176
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5473412
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Auto-Submit: Kimmo Kinnunen <kkinnunen@apple.com>
Commit-Queue: Kimmo Kinnunen <kkinnunen@apple.com>
Reviewed-by: Kimmo Kinnunen <kkinnunen@apple.com>

3 files changed, 62 insertions, 6 deletions

diff --git a/src/compiler/translator/msl/Name.cpp b/src/compiler/translator/msl/Name.cpp
index 9dc3b5481a..7faed0f5ba 100644
--- a/src/compiler/translator/msl/Name.cpp
+++ b/src/compiler/translator/msl/Name.cpp
@@ -96,13 +96,9 @@ void Name::emitImpl(T &out) const
             {
                 out << mRawName;
             }
-            else if (mRawName[0] != '_')
-            {
-                out << kAngleInternalPrefix << '_' << mRawName;
-            }
             else
             {
-                out << kAngleInternalPrefix << mRawName;
+                out << kAngleInternalPrefix << '_' << mRawName;
             }
             break;
 
diff --git a/src/compiler/translator/msl/TranslatorMSL.cpp b/src/compiler/translator/msl/TranslatorMSL.cpp
index 73fb34d17f..06d309e1ad 100644
--- a/src/compiler/translator/msl/TranslatorMSL.cpp
+++ b/src/compiler/translator/msl/TranslatorMSL.cpp
@@ -520,7 +520,7 @@ void AddFragDepthEXTDeclaration(TCompiler &compiler, TIntermBlock &root, TSymbol
         // EXT_blend_func_extended usage, the exact variable may be unknown until the
         // program is linked.
         TVariable *alpha0 =
-            new TVariable(&symbolTable, sh::ImmutableString("_ALPHA0"),
+            new TVariable(&symbolTable, sh::ImmutableString("ALPHA0"),
                           StaticType::Get<EbtFloat, EbpUndefined, EvqSpecConst, 1, 1>(),
                           SymbolType::AngleInternal);
 
diff --git a/src/tests/gl_tests/GLSLTest.cpp b/src/tests/gl_tests/GLSLTest.cpp
index fde319d879..58feeaf77b 100644
--- a/src/tests/gl_tests/GLSLTest.cpp
+++ b/src/tests/gl_tests/GLSLTest.cpp
@@ -19231,6 +19231,66 @@ Foo foo(float bar)
     EXPECT_PIXEL_COLOR_EQ(0, 0, GLColor::green);
 }
 
+// Test that underscores in array names work with out arrays.
+TEST_P(GLSLTest_ES3, UnderscoresWorkWithOutArrays)
+{
+    GLuint fbo;
+    glGenFramebuffers(1, &fbo);
+    glBindFramebuffer(GL_DRAW_FRAMEBUFFER, fbo);
+
+    GLuint textures[4];
+    glGenTextures(4, textures);
+
+    for (size_t texIndex = 0; texIndex < ArraySize(textures); texIndex++)
+    {
+        glBindTexture(GL_TEXTURE_2D, textures[texIndex]);
+        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, getWindowWidth(), getWindowHeight(), 0, GL_RGBA,
+                     GL_UNSIGNED_BYTE, nullptr);
+    }
+
+    GLint maxDrawBuffers;
+    glGetIntegerv(GL_MAX_DRAW_BUFFERS, &maxDrawBuffers);
+    ASSERT_GE(maxDrawBuffers, 4);
+
+    GLuint readFramebuffer;
+    glGenFramebuffers(1, &readFramebuffer);
+    glBindFramebuffer(GL_READ_FRAMEBUFFER, readFramebuffer);
+
+    constexpr char kFS[] = R"(#version 300 es
+precision highp float;
+out vec4 _e[4];
+void main()
+{
+    _e[0] = vec4(1.0, 0.0, 0.0, 1.0);
+    _e[1] = vec4(0.0, 1.0, 0.0, 1.0);
+    _e[2] = vec4(0.0, 0.0, 1.0, 1.0);
+    _e[3] = vec4(1.0, 1.0, 1.0, 1.0);
+}
+)";
+    ANGLE_GL_PROGRAM(program, essl3_shaders::vs::Simple(), kFS);
+    GLenum allBufs[4] = {GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1, GL_COLOR_ATTACHMENT2,
+                         GL_COLOR_ATTACHMENT3};
+    constexpr GLuint kMaxBuffers = 4;
+    // Enable all draw buffers.
+    for (GLuint texIndex = 0; texIndex < kMaxBuffers; texIndex++)
+    {
+        glBindTexture(GL_TEXTURE_2D, textures[texIndex]);
+        glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + texIndex, GL_TEXTURE_2D,
+                               textures[texIndex], 0);
+        glFramebufferTexture2D(GL_READ_FRAMEBUFFER, GL_COLOR_ATTACHMENT0 + texIndex, GL_TEXTURE_2D,
+                               textures[texIndex], 0);
+    }
+    glDrawBuffers(kMaxBuffers, allBufs);
+
+    // Draw with simple program.
+    drawQuad(program, essl3_shaders::PositionAttrib(), 0.5f, 1.0f, true);
+    ASSERT_GL_NO_ERROR();
+    verifyAttachment2DColor(0, textures[0], GL_TEXTURE_2D, 0, GLColor::red);
+    verifyAttachment2DColor(1, textures[1], GL_TEXTURE_2D, 0, GLColor::green);
+    verifyAttachment2DColor(2, textures[2], GL_TEXTURE_2D, 0, GLColor::blue);
+    verifyAttachment2DColor(3, textures[3], GL_TEXTURE_2D, 0, GLColor::white);
+}
+
 }  // anonymous namespace
 
 ANGLE_INSTANTIATE_TEST_ES2_AND_ES3_AND(