Support more configurability in GN toolchains

tools/gn/substitution_writer.h

Index: tools/gn/substitution_writer.h
diff --git a/tools/gn/substitution_writer.h b/tools/gn/substitution_writer.h
index cd45566fdb988bf8d1088c81fcaf8b9d652e94cf..219f135635aee87eebb1cc7ea68b72b11931bbbf 100644
--- a/tools/gn/substitution_writer.h
+++ b/tools/gn/substitution_writer.h
@@ -18,11 +18,35 @@ class SourceDir;
 class SourceFile;
 class SubstitutionList;
 class SubstitutionPattern;
+class Target;
+class Tool;
 
 // Help text for script source expansion.
 extern const char kSourceExpansion_Help[];
 
 // This class handles writing or applying substitution patterns to strings.
+//
+// There are several different uses:
+//
+//  - Source substitutions: These are used to compute action_foreach
+//    outputs and arguments. Functions are provided to expand these in terms
+//    of both OutputFiles (for writing Ninja files) as well as SourceFiles
+//    (for computing lists used by code).
+//
+//  - Target substitutions: These are specific to the target+tool combination
+//    and are shared between the compiler and linker ones. It includes things
+//    like the target_gen_dir.
+//
+//  - Compiler substitutions: These are used to compute compiler outputs.
+//    It includes all source substitutions (since they depend on the various
+//    parts of the source file) as well as the target substitutions.
+//
+//  - Linker substitutions: These are used to compute linker outputs. It
+//    includes the target substitutions.
+//
+// The compiler and linker specific substitutions do NOT include the various
+// cflags, ldflags, libraries, etc. These are written by the ninja target
+// writer since they depend on traversing the dependency tree.
 class SubstitutionWriter {
  public:
   enum OutputStyle {
@@ -30,15 +54,20 @@ class SubstitutionWriter {
     OUTPUT_RELATIVE,  // Dirs will be relative to a given directory.
   };
 
-  SubstitutionWriter();
-  ~SubstitutionWriter();
+  // Writes the pattern to the given stream with no special handling, and with
+  // Ninja variables replacing the patterns.
+  static void WriteWithNinjaVariables(
+      const SubstitutionPattern& pattern,
+      const EscapeOptions& escape_options,
+      std::ostream& out);
+
+  // NOP substitutions ---------------------------------------------------------
 
   // Converts the given SubstitutionList to OutputFiles assuming there are
   // no substitutions (it will assert if there are). This is used for cases
   // like actions where the outputs are explicit, but the list is stored as
   // a SubstitutionList.
   static void GetListAsSourceFiles(
-      const Settings* settings,
       const SubstitutionList& list,
       std::vector<SourceFile>* output);
   static void GetListAsOutputFiles(
@@ -46,6 +75,8 @@ class SubstitutionWriter {
       const SubstitutionList& list,
       std::vector<OutputFile>* output);
 
+  // Source substitutions -----------------------------------------------------
+
   // Applies the substitution pattern to a source file, returning the result
   // as either a string, a SourceFile or an OutputFile. If the result is
   // expected to be a SourceFile or an OutputFile, this will CHECK if the
@@ -115,13 +146,6 @@ class SubstitutionWriter {
       const EscapeOptions& escape_options,
       std::ostream& out);
 
-  // Writes the pattern to the given stream with no special handling, and with
-  // Ninja variables replacing the patterns.
-  static void WriteWithNinjaVariables(
-      const SubstitutionPattern& pattern,
-      const EscapeOptions& escape_options,
-      std::ostream& out);
-
   // Extracts the given type of substitution related to a source file from the
   // given source file. If output_style is OUTPUT_RELATIVE, relative_to
   // indicates the directory that the relative directories should be relative
@@ -132,6 +156,75 @@ class SubstitutionWriter {
       SubstitutionType type,
       OutputStyle output_style,
       const SourceDir& relative_to);
+
+  // Target substitutions ------------------------------------------------------
+  //
+  // Handles the target substitutions that apply to both compiler and linker
+  // tools.
+  static OutputFile ApplyPatternToTargetAsOutputFile(
+      const Target* target,
+      const Tool* tool,
+      const SubstitutionPattern& pattern);
+  static void ApplyListToTargetAsOutputFile(
+      const Target* target,
+      const Tool* tool,
+      const SubstitutionList& list,
+      std::vector<OutputFile>* output);
+
+  // This function is slightly different than the other substitution getters
+  // since it can handle failure (since it is designed to be used by the
+  // compiler and linker ones which will fall through if it's not a common tool
+  // one).
+  static bool GetTargetSubstitution(
+      const Target* target,
+      SubstitutionType type,
+      std::string* result);
+  static std::string GetTargetSubstitution(
+      const Target* target,
+      SubstitutionType type);
+
+  // Compiler substitutions ----------------------------------------------------
+  //
+  // A compiler substitution allows both source and tool substitutions. These
+  // are used to compute output names for compiler tools.
+
+  static OutputFile ApplyPatternToCompilerAsOutputFile(
+      const Target* target,
+      const SourceFile& source,
+      const SubstitutionPattern& pattern);
+  static void ApplyListToCompilerAsOutputFile(
+      const Target* target,
+      const SourceFile& source,
+      const SubstitutionList& list,
+      std::vector<OutputFile>* output);
+
+  // Like GetSourceSubstitution but for strings based on the target or
+  // toolchain. This type of result will always be relative to the build
+  // directory.
+  static std::string GetCompilerSubstitution(
+      const Target* target,
+      const SourceFile& source,
+      SubstitutionType type);
+
+  // Linker substitutions ------------------------------------------------------
+
+  static OutputFile ApplyPatternToLinkerAsOutputFile(
+      const Target* target,
+      const Tool* tool,
+      const SubstitutionPattern& pattern);
+  static void ApplyListToLinkerAsOutputFile(
+      const Target* target,
+      const Tool* tool,
+      const SubstitutionList& list,
+      std::vector<OutputFile>* output);
+
+  // Like GetSourceSubstitution but for strings based on the target or
+  // toolchain. This type of result will always be relative to the build
+  // directory.
+  static std::string GetLinkerSubstitution(
+      const Target* target,
+      const Tool* tool,
+      SubstitutionType type);
 };
 
 #endif  // TOOLS_GN_SUBSTITUTION_WRITER_H_