From b43bdaff3c13fe2273ec407797ff05db89bf3761 Mon Sep 17 00:00:00 2001
From: Ben Boeckel <ben.boeckel@kitware.com>
Date: Thu, 2 Jun 2022 17:20:05 -0400
Subject: cmCxxModuleMapper: implement support for GCC's module map format

---
 Source/cmCxxModuleMapper.cxx | 46 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

(limited to 'Source/cmCxxModuleMapper.cxx')

diff --git a/Source/cmCxxModuleMapper.cxx b/Source/cmCxxModuleMapper.cxx
index ddb95e38dd..94ad721702 100644
--- a/Source/cmCxxModuleMapper.cxx
+++ b/Source/cmCxxModuleMapper.cxx
@@ -3,6 +3,8 @@
 #include "cmCxxModuleMapper.h"
 
 #include <cassert>
+#include <sstream>
+#include <vector>
 
 #include "cmScanDepFormat.h"
 
@@ -15,9 +17,48 @@ cm::optional<std::string> CxxModuleLocations::BmiGeneratorPathForModule(
   return {};
 }
 
+namespace {
+
+std::string CxxModuleMapContentGcc(CxxModuleLocations const& loc,
+                                   cmScanDepInfo const& obj)
+{
+  std::stringstream mm;
+
+  // Documented in GCC's documentation. The format is a series of
+  // lines with a module name and the associated filename separated
+  // by spaces. The first line may use `$root` as the module name
+  // to specify a "repository root". That is used to anchor any
+  // relative paths present in the file (CMake should never
+  // generate any).
+
+  // Write the root directory to use for module paths.
+  mm << "$root " << loc.RootDirectory << "\n";
+
+  for (auto const& p : obj.Provides) {
+    if (auto bmi_loc = loc.BmiGeneratorPathForModule(p.LogicalName)) {
+      mm << p.LogicalName << ' ' << *bmi_loc << '\n';
+    }
+  }
+  for (auto const& r : obj.Requires) {
+    if (auto bmi_loc = loc.BmiGeneratorPathForModule(r.LogicalName)) {
+      mm << r.LogicalName << ' ' << *bmi_loc << '\n';
+    }
+  }
+
+  return mm.str();
+}
+}
+
 cm::static_string_view CxxModuleMapExtension(
   cm::optional<CxxModuleMapFormat> format)
 {
+  if (format) {
+    switch (*format) {
+      case CxxModuleMapFormat::Gcc:
+        return ".gcm"_s;
+    }
+  }
+
   return ".bmi"_s;
 }
 
@@ -25,6 +66,11 @@ std::string CxxModuleMapContent(CxxModuleMapFormat format,
                                 CxxModuleLocations const& loc,
                                 cmScanDepInfo const& obj)
 {
+  switch (format) {
+    case CxxModuleMapFormat::Gcc:
+      return CxxModuleMapContentGcc(loc, obj);
+  }
+
   assert(false);
   return {};
 }
-- 
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