[Fix] (MG_Util/ShaderTranspiler): keep #line directives instead of deleting them, dropping only the GLSL-illegal quoted filename and the ones that precede #version, so __LINE__ and compiler diagnostics follow the application's own numbering

MobileGL/MG_Test/Program/ProgramUtilTest.cpp

@@ -446,6 +446,9 @@ void main() {
     EXPECT_NE(versionPos, String::npos);
     EXPECT_EQ(outputPos, versionPos + std::strlen("#version 330 core\n"));
     EXPECT_NE(source.find("// #version 460 core"), String::npos);
+    // This #line sits ahead of the version directive, where GLSL would never have honoured it, so
+    // it is still dropped. Directives that follow the version line are kept - see
+    // PreprocessKeepsPlainLineDirectivesAndSparesLookalikeIdentifiers.
     EXPECT_EQ(source.find("#line"), String::npos);
 
     ShaderAttrib attrib{.shaderType = GL_FRAGMENT_SHADER, .sourceStr = source};
@@ -526,6 +529,34 @@ void main() {
     }
 }
 
+// KHR-GL33.shaders.preprocessor.builtin.line_* checks that __LINE__ follows #line. That only works
+// if the directive reaches glslang, so a plain integer form must pass through untouched - while
+// "#linear" and friends must not be mistaken for it.
+TEST_F(ProgramUtilTest, PreprocessKeepsPlainLineDirectivesAndSparesLookalikeIdentifiers) {
+    using namespace MG_Util::ShaderTranspiler;
+
+    String source = R"(#version 330 core
+out vec4 fragColor;
+#line 42
+float linear(float x) { return x; }
+void main() {
+#line 100
+    fragColor = vec4(linear(float(__LINE__)));
+}
+)";
+    PreprocessShaderSource(ShaderStage::Fragment, source);
+
+    EXPECT_NE(source.find("#line 42"), String::npos) << source;
+    EXPECT_NE(source.find("#line 100"), String::npos) << source;
+    EXPECT_NE(source.find("float linear(float x)"), String::npos) << "identifier lookalike was eaten:\n" << source;
+
+    ShaderAttrib attrib{.shaderType = GL_FRAGMENT_SHADER, .sourceStr = source};
+    auto res = ShaderCompiler::CompileShader(attrib);
+    if (!res) {
+        FAIL() << "errc: " << res.error().errc << "\nlog: " << res.error().log << "\nsource:\n" << source;
+    }
+}
+
 TEST_F(ProgramUtilTest, PreprocessModernSampleQualifierStaysAtVersion460) {
     using namespace MG_Util::ShaderTranspiler;
 

MobileGL/MG_Util/ShaderTranspiler/ShaderSourceProcessor.cpp

@@ -833,6 +833,58 @@ namespace {
         return info.HasVersionDirective() ? info.versionDirectiveEnd : 0;
     }
 
+    // GLSL's #line takes integer expressions only, but plenty of shader-pack preprocessors emit the
+    // C form with a quoted filename. Deleting every #line outright made those harmless - at the cost
+    // of __LINE__ reporting the position in MobileGL's rewritten text rather than the one the pack
+    // author wrote, and of every later diagnostic pointing at the wrong line. Dropping just the
+    // quoted operand keeps the directive doing its job and still hands glslang something it accepts.
+    void NormalizeLineDirectives(MobileGL::String& source) {
+        const MobileGL::String masked = MaskCommentsAndQuotedText(source);
+        const SizeT versionEnd = FindAfterVersionDirective(source);
+        MobileGL::String result;
+        result.reserve(source.size());
+
+        SizeT lineStart = 0;
+        while (lineStart <= source.size()) {
+            SizeT lineEnd = source.find('\n', lineStart);
+            const bool lastLine = lineEnd == MobileGL::String::npos;
+            if (lastLine) lineEnd = source.size();
+
+            SizeT probe = lineStart;
+            while (probe < lineEnd && (source[probe] == ' ' || source[probe] == '\t')) probe++;
+
+            const bool isLineDirective = masked.compare(probe, 5, "#line") == 0 &&
+                                         (probe + 5 >= lineEnd || !IsIdentifierChar(source[probe + 5]));
+            if (isLineDirective && lineStart < versionEnd) {
+                // #version has to be the first token in the shader, so a #line ahead of it could
+                // never have taken effect. Drop it rather than hand glslang a source it must reject
+                // - some pack preprocessors emit their directives before the version line.
+            } else if (isLineDirective) {
+                // Keep everything up to the first quote that the masker identified as string text.
+                SizeT quotePos = MobileGL::String::npos;
+                for (SizeT i = probe + 5; i < lineEnd; i++) {
+                    if (source[i] == '"' || source[i] == '\'') {
+                        quotePos = i;
+                        break;
+                    }
+                }
+                if (quotePos != MobileGL::String::npos) {
+                    result.append(source, lineStart, quotePos - lineStart);
+                } else {
+                    result.append(source, lineStart, lineEnd - lineStart);
+                }
+            } else {
+                result.append(source, lineStart, lineEnd - lineStart);
+            }
+
+            if (lastLine) break;
+            result.push_back('\n');
+            lineStart = lineEnd + 1;
+        }
+
+        source = std::move(result);
+    }
+
     bool IsExtensionAdvertised(MobileGL::GLExtension extension) {
         const auto& activeBackendObject = MobileGL::MG_Backend::pActiveBackendObject;
         if (!activeBackendObject) {
@@ -1154,19 +1206,7 @@ namespace MobileGL {
 
                 BlankBlockComments(source);
 
-                // remove #line directives
+                NormalizeLineDirectives(source);
-                SizeT linedirPos = source.find("#line");
-                while (linedirPos != String::npos) {
-                    SizeT newlinePos = source.find('\n', linedirPos);
-                    if (newlinePos == String::npos) {
-                        source.erase(linedirPos);
-                        break;
-                    }
-
-                    // Preserve a line break so adjacent preprocessor directives do not merge.
-                    source = source.replace(linedirPos, newlinePos - linedirPos + 1, "\n");
-                    linedirPos = source.find("#line", linedirPos);
-                }
 
                 // remove "noperspective"
                 const char* str_np = "noperspective";