Wire up compiler frontend.

engine/src/flutter/impeller/compiler/BUILD.gn

@@ -11,6 +11,8 @@ source_set("compiler_lib") {
     "logger.h",
     "reflector.cc",
     "reflector.h",
+    "switches.cc",
+    "switches.h",
   ]
 
   public_deps = [
@@ -22,14 +24,16 @@ source_set("compiler_lib") {
   ]
 }
 
-executable("compiler") {
-  output_name = "impellerc"
-
+executable("impellerc") {
   sources = [ "impellerc_main.cc" ]
 
   deps = [ ":compiler_lib" ]
 }
 
+group("compiler") {
+  deps = [ ":impellerc" ]
+}
+
 test_fixtures("compiler_test_fixtures") {
   fixtures = [
     "fixtures/sample.frag",

engine/src/flutter/impeller/compiler/impellerc_main.cc

@@ -3,14 +3,65 @@
 // found in the LICENSE file.
 
 #include "flutter/fml/command_line.h"
+#include "flutter/fml/file.h"
 #include "flutter/fml/macros.h"
+#include "flutter/fml/mapping.h"
+#include "flutter/impeller/compiler/compiler.h"
+#include "flutter/impeller/compiler/switches.h"
 #include "third_party/shaderc/libshaderc/include/shaderc/shaderc.hpp"
 
 namespace impeller {
 namespace compiler {
 
 bool Main(const fml::CommandLine& command_line) {
-  return false;
+  if (command_line.HasOption("help")) {
+    Switches::PrintHelp(std::cout);
+    return true;
+  }
+
+  Switches switches(command_line);
+  if (!switches.AreValid(std::cerr)) {
+    std::cerr << "Invalid flags specified." << std::endl;
+    Switches::PrintHelp(std::cerr);
+    return false;
+  }
+
+  auto source_file_mapping = fml::FileMapping::CreateReadOnly(
+      *switches.working_directory, switches.source_file_name);
+  if (!source_file_mapping) {
+    std::cerr << "Could not open input file." << std::endl;
+    return false;
+  }
+
+  Compiler::SourceOptions options;
+  options.type = Compiler::SourceTypeFromFileName(switches.source_file_name);
+  options.working_directory = switches.working_directory;
+  options.file_name = switches.source_file_name;
+
+  Compiler compiler(*source_file_mapping, options);
+  if (!compiler.IsValid()) {
+    std::cerr << "Compilation failed." << std::endl;
+    std::cerr << compiler.GetErrorMessages() << std::endl;
+    return false;
+  }
+
+  if (!fml::WriteAtomically(*switches.working_directory,
+                            switches.spirv_file_name.c_str(),
+                            *compiler.GetSPIRVAssembly())) {
+    std::cerr << "Could not write file to " << switches.spirv_file_name
+              << std::endl;
+    return false;
+  }
+
+  if (!fml::WriteAtomically(*switches.working_directory,
+                            switches.metal_file_name.c_str(),
+                            *compiler.GetMSLShaderSource())) {
+    std::cerr << "Could not write file to " << switches.spirv_file_name
+              << std::endl;
+    return false;
+  }
+
+  return true;
 }
 
 }  // namespace compiler

engine/src/flutter/impeller/compiler/switches.cc

@@ -0,0 +1,59 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/impeller/compiler/switches.h"
+
+#include <filesystem>
+
+#include "flutter/fml/file.h"
+
+namespace impeller {
+namespace compiler {
+
+void Switches::PrintHelp(std::ostream& stream) {
+  stream << std::endl << "Valid Argument are:" << std::endl;
+  stream << "--input=<glsl_file>" << std::endl;
+  stream << "--metal=<metal_output_file>" << std::endl;
+  stream << "--spirv=<spirv_output_file>" << std::endl;
+}
+
+Switches::Switches() = default;
+
+Switches::~Switches() = default;
+
+Switches::Switches(const fml::CommandLine& 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))),
+      source_file_name(command_line.GetOptionValueWithDefault("input", "")),
+      metal_file_name(command_line.GetOptionValueWithDefault("metal", "")),
+      spirv_file_name(command_line.GetOptionValueWithDefault("spirv", "")) {}
+
+bool Switches::AreValid(std::ostream& explain) const {
+  bool valid = true;
+  if (!working_directory || !working_directory->is_valid()) {
+    explain << "Could not figure out working directory." << std::endl;
+    valid = false;
+  }
+
+  if (source_file_name.empty()) {
+    explain << "Input file name was empty." << std::endl;
+    valid = false;
+  }
+
+  if (metal_file_name.empty()) {
+    explain << "Metal file name was empty." << std::endl;
+    valid = false;
+  }
+
+  if (spirv_file_name.empty()) {
+    explain << "Spirv file name was empty." << std::endl;
+    valid = false;
+  }
+  return valid;
+}
+
+}  // namespace compiler
+}  // namespace impeller

engine/src/flutter/impeller/compiler/switches.h

@@ -0,0 +1,35 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#pragma once
+
+#include <iostream>
+#include <memory>
+
+#include "flutter/fml/command_line.h"
+#include "flutter/fml/macros.h"
+#include "flutter/fml/unique_fd.h"
+
+namespace impeller {
+namespace compiler {
+
+struct Switches {
+  std::shared_ptr<fml::UniqueFD> working_directory;
+  std::string source_file_name;
+  std::string metal_file_name;
+  std::string spirv_file_name;
+
+  Switches();
+
+  ~Switches();
+
+  Switches(const fml::CommandLine& command_line);
+
+  bool AreValid(std::ostream& explain) const;
+
+  static void PrintHelp(std::ostream& stream);
+};
+
+}  // namespace compiler
+}  // namespace impeller

engine/src/flutter/impeller/compiler/tools/compiler.gni

@@ -2,6 +2,32 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/compiled_action.gni")
+
 template("impeller_shaders") {
-  assert(defined(invoker.shaders), "Impeller shaders must be specified.")
+  compiled_action_foreach(target_name) {
+    assert(defined(invoker.shaders), "Impeller shaders must be specified.")
+
+    tool = "//flutter/impeller/compiler:impellerc"
+
+    sources = invoker.shaders
+
+    metal_intermediate = "$target_gen_dir/{{source_file_part}}.metal"
+    spirv_intermediate = "$target_gen_dir/{{source_file_part}}.spirv"
+
+    outputs = [
+      metal_intermediate,
+      spirv_intermediate,
+    ]
+
+    source_path = "{{source}}"
+    metal_intermediate_path = rebase_path(metal_intermediate, root_build_dir)
+    spirv_intermediate_path = rebase_path(spirv_intermediate, root_build_dir)
+
+    args = [
+      "--input=$source_path",
+      "--metal=$metal_intermediate_path",
+      "--spirv=$spirv_intermediate_path",
+    ]
+  }
 }

engine/src/flutter/impeller/impeller/BUILD.gn

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//flutter/common/config.gni")
+import("//flutter/impeller/compiler/tools/compiler.gni")
 
 config("impeller_config") {
   include_dirs = [ ".." ]
@@ -86,6 +87,7 @@ source_set("impeller") {
       compositor_sources + geometry_sources + entity_sources + image_sources
 
   deps = [
+    ":shaders",
     "//flutter/fml",
     "//flutter/impeller/third_party/stb",
     "//flutter/runtime:libdart",  # For tracing, seems to be pulled in by FML.