Forward targets specification to the code generator in impellerc.

impeller/compiler/compiler.cc

@@ -198,6 +198,19 @@ static spv::ExecutionModel ToExecutionModel(Compiler::SourceType type) {
   ;
 }
 
+static spirv_cross::CompilerMSL::Options::Platform
+CompilerTargetPlatformToCompilerMSLTargetPlatform(
+    Compiler::TargetPlatform platform) {
+  switch (platform) {
+    case Compiler::TargetPlatform::kIPhoneOS:
+      return spirv_cross::CompilerMSL::Options::Platform::iOS;
+    case Compiler::TargetPlatform::kMacOS:
+    // Unknown should not happen due to prior validation.
+    case Compiler::TargetPlatform::kUnknown:
+      return spirv_cross::CompilerMSL::Options::Platform::macOS;
+  }
+}
+
 Compiler::Compiler(const fml::Mapping& source_mapping,
                    SourceOptions source_options,
                    Reflector::Options reflector_options)
@@ -208,6 +221,11 @@ Compiler::Compiler(const fml::Mapping& source_mapping,
     return;
   }
 
+  if (source_options.target_platform == TargetPlatform::kUnknown) {
+    COMPILER_ERROR << "Target platform not specified.";
+    return;
+  }
+
   auto shader_kind = ToShaderCShaderKind(source_options.type);
 
   if (shader_kind == shaderc_shader_kind::shaderc_glsl_infer_from_source) {
@@ -297,7 +315,8 @@ Compiler::Compiler(const fml::Mapping& source_mapping,
 
   {
     spirv_cross::CompilerMSL::Options msl_options;
-    msl_options.platform = spirv_cross::CompilerMSL::Options::Platform::macOS;
+    msl_options.platform = CompilerTargetPlatformToCompilerMSLTargetPlatform(
+        options_.target_platform);
     // If this version specification changes, the GN rules that process the
     // Metal to AIR must be updated as well.
     msl_options.msl_version =

impeller/compiler/compiler.h

@@ -27,13 +27,20 @@ class Compiler {
     kFragmentShader,
   };
 
+  enum class TargetPlatform {
+    kUnknown,
+    kMacOS,
+    kIPhoneOS,
+  };
+
   static SourceType SourceTypeFromFileName(const std::string& file_name);
 
   static std::string EntryPointFromSourceName(const std::string& file_name,
                                               SourceType type);
 
   struct SourceOptions {
     SourceType type = SourceType::kUnknown;
+    TargetPlatform target_platform = TargetPlatform::kUnknown;
     std::shared_ptr<fml::UniqueFD> working_directory;
     std::vector<IncludeDir> include_dirs;
     std::string file_name = "main.glsl";

impeller/compiler/impellerc_main.cc

@@ -37,6 +37,7 @@ bool Main(const fml::CommandLine& command_line) {
   }
 
   Compiler::SourceOptions options;
+  options.target_platform = switches.target_platform;
   options.type = Compiler::SourceTypeFromFileName(switches.source_file_name);
   options.working_directory = switches.working_directory;
   options.file_name = switches.source_file_name;

impeller/compiler/switches.cc

@@ -5,14 +5,25 @@
 #include "flutter/impeller/compiler/switches.h"
 
 #include <filesystem>
+#include <map>
 
 #include "flutter/fml/file.h"
 
 namespace impeller {
 namespace compiler {
 
+static const std::map<std::string, Compiler::TargetPlatform> kKnownPlatforms = {
+    {"macos", Compiler::TargetPlatform::kMacOS},
+    {"ios", Compiler::TargetPlatform::kIPhoneOS},
+};
+
 void Switches::PrintHelp(std::ostream& stream) {
   stream << std::endl << "Valid Argument are:" << std::endl;
+  stream << "One of [";
+  for (const auto& platform : kKnownPlatforms) {
+    stream << " --" << platform.first;
+  }
+  stream << " ]" << std::endl;
   stream << "--input=<glsl_file>" << std::endl;
   stream << "--metal=<metal_output_file>" << std::endl;
   stream << "--spirv=<spirv_output_file>" << std::endl;
@@ -28,8 +39,27 @@ Switches::Switches() = default;
 
 Switches::~Switches() = default;
 
+static Compiler::TargetPlatform TargetPlatformFromCommandLine(
+    const fml::CommandLine& command_line) {
+  auto target = Compiler::TargetPlatform::kUnknown;
+  for (const auto& platform : kKnownPlatforms) {
+    if (command_line.HasOption(platform.first)) {
+      // If the platform has already been determined, the caller may have
+      // specified multiple platforms. This is an error and only one must be
+      // selected.
+      if (target != Compiler::TargetPlatform::kUnknown) {
+        return Compiler::TargetPlatform::kUnknown;
+      }
+      target = platform.second;
+      // Keep going to detect duplicates.
+    }
+  }
+  return target;
+}
+
 Switches::Switches(const fml::CommandLine& command_line)
-    : working_directory(std::make_shared<fml::UniqueFD>(
+    : target_platform(TargetPlatformFromCommandLine(command_line)),
+      working_directory(std::make_shared<fml::UniqueFD>(
           fml::OpenDirectory(std::filesystem::current_path().native().c_str(),
                              false,  // create if necessary,
                              fml::FilePermission::kRead))),
@@ -67,6 +97,11 @@ Switches::Switches(const fml::CommandLine& command_line)
 
 bool Switches::AreValid(std::ostream& explain) const {
   bool valid = true;
+  if (target_platform == Compiler::TargetPlatform::kUnknown) {
+    explain << "The target platform (only one) was not specified." << std::endl;
+    valid = false;
+  }
+
   if (!working_directory || !working_directory->is_valid()) {
     explain << "Could not figure out working directory." << std::endl;
     valid = false;

impeller/compiler/switches.h

@@ -10,12 +10,14 @@
 #include "flutter/fml/command_line.h"
 #include "flutter/fml/macros.h"
 #include "flutter/fml/unique_fd.h"
+#include "flutter/impeller/compiler/compiler.h"
 #include "flutter/impeller/compiler/include_dir.h"
 
 namespace impeller {
 namespace compiler {
 
 struct Switches {
+  Compiler::TargetPlatform target_platform = Compiler::TargetPlatform::kUnknown;
   std::shared_ptr<fml::UniqueFD> working_directory;
   std::vector<IncludeDir> include_directories;
   std::string source_file_name;

impeller/tools/impeller.gni

@@ -142,6 +142,13 @@ template("impeller_shaders") {
       "--include={{source_dir}}",
       "--depfile=$depfile_intermediate_path",
     ]
+
+    if (is_mac) {
+      args += [ "--macos" ]
+    }
+    if (is_ios) {
+      args += [ "--ios" ]
+    }
   }
 
   metal_library_target_name = "metal_library_$target_name"