cmTarget: add support for C++ module fileset types

C++ modules have two variants which are of importance to CMake:

  - `CXX_MODULES`: interface modules (those using `export module M;`,
    `export module M:part;`, or `module M:internal_part;`)
  - `CXX_MODULE_HEADER_UNITS`: importable header units

Creating C++ modules or partitions are *not* supported in any other
source listing. This is because the source files must be installed (so
their scope matters), but not part of usage requirements (what it means
for a module source to be injected into a consumer is not clear at this
moment). Due to the way `FILE_SET` works with scopes, they are a perfect
fit as long as `INTERFACE` is not allowed (which it is not).

1 files changed, 79 insertions, 0 deletions

diff --git a/Source/cmTarget.cxx b/Source/cmTarget.cxx
index 83dc1c2..4a94dc6 100644
--- a/Source/cmTarget.cxx
+++ b/Source/cmTarget.cxx
@@ -272,6 +272,8 @@ public:
   cmListFileBacktrace Backtrace;
 
   FileSetType HeadersFileSets;
+  FileSetType CxxModulesFileSets;
+  FileSetType CxxModuleHeadersFileSets;
 
   cmTargetInternals();
 
@@ -301,6 +303,19 @@ cmTargetInternals::cmTargetInternals()
                     "The default header set"_s, "Header set"_s,
                     FileSetEntries("HEADER_SETS"_s),
                     FileSetEntries("INTERFACE_HEADER_SETS"_s))
+  , CxxModulesFileSets("CXX_MODULES"_s, "CXX_MODULE_DIRS"_s,
+                       "CXX_MODULE_SET"_s, "CXX_MODULE_DIRS_"_s,
+                       "CXX_MODULE_SET_"_s, "C++ module"_s,
+                       "The default C++ module set"_s, "C++ module set"_s,
+                       FileSetEntries("CXX_MODULE_SETS"_s),
+                       FileSetEntries("INTERFACE_CXX_MODULE_SETS"_s))
+  , CxxModuleHeadersFileSets(
+      "CXX_MODULE_HEADER_UNITS"_s, "CXX_MODULE_HEADER_UNIT_DIRS"_s,
+      "CXX_MODULE_HEADER_UNIT_SET"_s, "CXX_MODULE_HEADER_UNIT_DIRS_"_s,
+      "CXX_MODULE_HEADER_UNIT_SET_"_s, "C++ module header"_s,
+      "The default C++ module header set"_s, "C++ module header set"_s,
+      FileSetEntries("CXX_MODULE_HEADER_UNIT_SETS"_s),
+      FileSetEntries("INTERFACE_CXX_MODULE_HEADER_UNIT_SETS"_s))
 {
 }
 
@@ -1366,11 +1381,32 @@ cmBTStringRange cmTarget::GetHeaderSetsEntries() const
   return cmMakeRange(this->impl->HeadersFileSets.SelfEntries.Entries);
 }
 
+cmBTStringRange cmTarget::GetCxxModuleSetsEntries() const
+{
+  return cmMakeRange(this->impl->CxxModulesFileSets.SelfEntries.Entries);
+}
+
+cmBTStringRange cmTarget::GetCxxModuleHeaderSetsEntries() const
+{
+  return cmMakeRange(this->impl->CxxModuleHeadersFileSets.SelfEntries.Entries);
+}
+
 cmBTStringRange cmTarget::GetInterfaceHeaderSetsEntries() const
 {
   return cmMakeRange(this->impl->HeadersFileSets.InterfaceEntries.Entries);
 }
 
+cmBTStringRange cmTarget::GetInterfaceCxxModuleSetsEntries() const
+{
+  return cmMakeRange(this->impl->CxxModulesFileSets.InterfaceEntries.Entries);
+}
+
+cmBTStringRange cmTarget::GetInterfaceCxxModuleHeaderSetsEntries() const
+{
+  return cmMakeRange(
+    this->impl->CxxModuleHeadersFileSets.InterfaceEntries.Entries);
+}
+
 namespace {
 #define MAKE_PROP(PROP) const std::string prop##PROP = #PROP
 MAKE_PROP(C_STANDARD);
@@ -1630,6 +1666,12 @@ void cmTarget::StoreProperty(const std::string& prop, ValueType value)
   } else if (this->impl->HeadersFileSets.WriteProperties(
                this, this->impl.get(), prop, value, true)) {
     /* Handled in the `if` condition. */
+  } else if (this->impl->CxxModulesFileSets.WriteProperties(
+               this, this->impl.get(), prop, value, true)) {
+    /* Handled in the `if` condition. */
+  } else if (this->impl->CxxModuleHeadersFileSets.WriteProperties(
+               this, this->impl.get(), prop, value, true)) {
+    /* Handled in the `if` condition. */
   } else {
     this->impl->Properties.SetProperty(prop, value);
   }
@@ -1741,6 +1783,13 @@ void cmTarget::AppendProperty(const std::string& prop,
     this->impl->Makefile->IssueMessage(
       MessageType::FATAL_ERROR, prop + " property may not be appended.");
   } else if (this->impl->HeadersFileSets.WriteProperties(
+               this, this->impl.get(), prop, value,
+               false)) { // NOLINT(bugprone-branch-clone)
+    /* Handled in the `if` condition. */
+  } else if (this->impl->CxxModulesFileSets.WriteProperties(
+               this, this->impl.get(), prop, value, false)) {
+    /* Handled in the `if` condition. */
+  } else if (this->impl->CxxModuleHeadersFileSets.WriteProperties(
                this, this->impl.get(), prop, value, false)) {
     /* Handled in the `if` condition. */
   } else {
@@ -2249,6 +2298,17 @@ cmValue cmTarget::GetProperty(const std::string& prop) const
     if (headers.first) {
       return headers.second;
     }
+    auto cxx_modules = this->impl->CxxModulesFileSets.ReadProperties(
+      this, this->impl.get(), prop);
+    if (cxx_modules.first) {
+      return cxx_modules.second;
+    }
+    auto cxx_module_headers =
+      this->impl->CxxModuleHeadersFileSets.ReadProperties(
+        this, this->impl.get(), prop);
+    if (cxx_module_headers.first) {
+      return cxx_module_headers.second;
+    }
   }
 
   cmValue retVal = this->impl->Properties.GetPropertyValue(prop);
@@ -2526,6 +2586,11 @@ std::pair<cmFileSet*, bool> cmTarget::GetOrCreateFileSet(
     auto bt = this->impl->Makefile->GetBacktrace();
     if (type == this->impl->HeadersFileSets.TypeName) {
       this->impl->HeadersFileSets.AddFileSet(name, vis, std::move(bt));
+    } else if (type == this->impl->CxxModulesFileSets.TypeName) {
+      this->impl->CxxModulesFileSets.AddFileSet(name, vis, std::move(bt));
+    } else if (type == this->impl->CxxModuleHeadersFileSets.TypeName) {
+      this->impl->CxxModuleHeadersFileSets.AddFileSet(name, vis,
+                                                      std::move(bt));
     }
   }
   return std::make_pair(&result.first->second, result.second);
@@ -2536,6 +2601,12 @@ std::string cmTarget::GetFileSetsPropertyName(const std::string& type)
   if (type == "HEADERS") {
     return "HEADER_SETS";
   }
+  if (type == "CXX_MODULES") {
+    return "CXX_MODULE_SETS";
+  }
+  if (type == "CXX_MODULE_HEADER_UNITS") {
+    return "CXX_MODULE_HEADER_UNIT_SETS";
+  }
   return "";
 }
 
@@ -2544,6 +2615,12 @@ std::string cmTarget::GetInterfaceFileSetsPropertyName(const std::string& type)
   if (type == "HEADERS") {
     return "INTERFACE_HEADER_SETS";
   }
+  if (type == "CXX_MODULES") {
+    return "INTERFACE_CXX_MODULE_SETS";
+  }
+  if (type == "CXX_MODULE_HEADER_UNITS") {
+    return "INTERFACE_CXX_MODULE_HEADER_UNIT_SETS";
+  }
   return "";
 }
 
@@ -2571,6 +2648,8 @@ std::vector<std::string> cmTarget::GetAllInterfaceFileSets() const
   };
 
   appendEntries(this->impl->HeadersFileSets.InterfaceEntries.Entries);
+  appendEntries(this->impl->CxxModulesFileSets.InterfaceEntries.Entries);
+  appendEntries(this->impl->CxxModuleHeadersFileSets.InterfaceEntries.Entries);
 
   return result;
 }