[LLVM] Allow modulemap installation

[EricWF]

Summary

Currently we can't install the modulemaps provided by LLVM, since they are not structured to support headers generated as part of the build (ex. llvm/IR/Attributes.gen).
This patch restructures the module maps in order to support installation.

Modules containing generated headers are defined in the new module.extern.modulemap file, and are referenced from the main module.modulemap using extern module. There are two versions of the module.extern.modulemap file; one used when building and another, module.install.modulemap, which is re-named during installation.

Users can opt-into module map installation using -DLLVM_INSTALL_MODULEMAPS=ON. The default value is OFF due to llvm.org/PR31905.

[EricWF]

Ping. If this doesn't get any attention within a week, I'll land it for post-commit review.

[tschuett]

Thx, for doing this. Are you planning to do a follow up for Clang? I have been hacking this myself locally.

[EricWF]

In D53510#1301347, @tschuett wrote:

Thx, for doing this. Are you planning to do a follow up for Clang? I have been hacking this myself locally.

I hadn't planned on it (I don't strictly need it for my use case), but I'll look into a follow up commit.

Accepting for post-commit review.

CMakeLists.txt

 
 option(LLVM_INSTALL_BINUTILS_SYMLINKS
   "Install symlinks from the binutils tool names to the corresponding LLVM tools." OFF)
 
 option(LLVM_INSTALL_UTILS "Include utility binaries in the 'install' target." OFF)
 
 option(LLVM_INSTALL_TOOLCHAIN_ONLY "Only include toolchain files in the 'install' target." OFF)
 
+# Unfortunatly Clang is too eager to search directories for module maps, which can cause the
+# installed version of the maps to be found when building LLVM from source. Therefore we turn off
+# the installation by default. See llvm.org/PR31905.
+option(LLVM_INSTALL_MODULEMAPS "Install the modulemap files in the 'install' target." OFF)
+
 option(LLVM_USE_FOLDERS "Enable solution folders in Visual Studio. Disable for Express versions." ON)
 if ( LLVM_USE_FOLDERS )
   set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 endif()
 
 include(VersionFromVCS)
 
 option(LLVM_APPEND_VC_REV
install(DIRECTORY ${LLVM_INCLUDE_DIR}/llvm ${LLVM_INCLUDE_DIR}/llvm-c
     PATTERN "*.gen"
     PATTERN "*.inc"
     # Exclude include/llvm/CMakeFiles/intrinsics_gen.dir, matched by "*.def"
     PATTERN "CMakeFiles" EXCLUDE
     PATTERN "config.h" EXCLUDE
     PATTERN ".svn" EXCLUDE
     )
 
+  if (LLVM_INSTALL_MODULEMAPS)
+    install(DIRECTORY include/llvm include/llvm-c
+            DESTINATION include
+            COMPONENT llvm-headers
+            FILES_MATCHING
+            PATTERN "module.modulemap"
+            )
+    install(FILES include/llvm/module.install.modulemap
+            DESTINATION include/llvm
+            COMPONENT llvm-headers
+            RENAME "module.extern.modulemap"
+            )
+  endif(LLVM_INSTALL_MODULEMAPS)
+
   # Installing the headers needs to depend on generating any public
   # tablegen'd headers.
   add_custom_target(llvm-headers DEPENDS intrinsics_gen)
   set_target_properties(llvm-headers PROPERTIES FOLDER "Misc")
 
   if (NOT LLVM_ENABLE_IDE)
     add_llvm_install_targets(install-llvm-headers
                              DEPENDS llvm-headers

include/llvm/module.extern.modulemap

+module LLVM_Extern_Config_Def {}
+module LLVM_Extern_IR_Attributes_Gen {}
+module LLVM_Extern_IR_Intrinsics_Gen {}
+module LLVM_Extern_IR_Intrinsics_Enum {}
+module LLVM_Extern_Utils_DataTypes {}

include/llvm/module.install.modulemap

+
+module LLVM_Extern_Config_Def {
+ textual header "Config/AsmParsers.def"
+ textual header "Config/AsmPrinters.def"
+ textual header "Config/Disassemblers.def"
+ textual header "Config/Targets.def"
+ export *
+}
+
+module LLVM_Extern_IR_Attributes_Gen {
+  textual header "IR/Attributes.gen"
+  textual header "IR/Attributes.inc"
+}
+
+module LLVM_Extern_IR_Intrinsics_Gen {
+  textual header "IR/Intrinsics.gen"
+  textual header "IR/Intrinsics.inc"
+}
+
+module LLVM_Extern_IR_Intrinsics_Enum {
+  textual header "IR/IntrinsicEnums.inc"
+}
+
+module LLVM_Extern_Utils_DataTypes {
+  header "Support/DataTypes.h"
+  export *
+}

include/llvm/module.modulemap

module LLVM_Backend {
   module Target {
     umbrella "Target"
     module * { export * }
   }
 }
 
 module LLVM_Bitcode { requires cplusplus umbrella "Bitcode" module * { export * } }
 
+
 module LLVM_BinaryFormat {
     requires cplusplus
     umbrella "BinaryFormat" module * { export * }
     textual header "BinaryFormat/Dwarf.def"
     textual header "BinaryFormat/DynamicTags.def"
     textual header "BinaryFormat/MachO.def"
     textual header "BinaryFormat/ELFRelocs/AArch64.def"
     textual header "BinaryFormat/ELFRelocs/AMDGPU.def"
module LLVM_BinaryFormat {
     textual header "BinaryFormat/ELFRelocs/RISCV.def"
     textual header "BinaryFormat/ELFRelocs/Sparc.def"
     textual header "BinaryFormat/ELFRelocs/SystemZ.def"
     textual header "BinaryFormat/ELFRelocs/x86_64.def"
     textual header "BinaryFormat/WasmRelocs.def"
     textual header "BinaryFormat/MsgPack.def"
 }
 
-module LLVM_Config { requires cplusplus umbrella "Config" module * { export * } }
+module LLVM_Config {
+  requires cplusplus
+  umbrella "Config"
+  extern module LLVM_Extern_Config_Def "module.extern.modulemap"
+  module * { export * }
+}
 
 module LLVM_DebugInfo {
   requires cplusplus
   module DIContext { header "DebugInfo/DIContext.h" export * }
 }
 
 module LLVM_DebugInfo_DWARF {
   requires cplusplus

 module LLVM_intrinsic_gen {
   requires cplusplus
 
   // Delay building the modules containing dependencies to Attributes.h and
   // Intrinsics.h because they need to be generated by tablegen first.
 
   // Attributes.h
   module IR_Argument { header "IR/Argument.h" export * }
-  module IR_Attributes { header "IR/Attributes.h" export * }
+  module IR_Attributes {
+    header "IR/Attributes.h"
+    extern module LLVM_Extern_IR_Attributes_Gen "module.extern.modulemap"
+    export *
+  }
   module IR_CallSite { header "IR/CallSite.h" export * }
   module IR_ConstantFolder { header "IR/ConstantFolder.h" export * }
   module IR_GlobalVariable { header "IR/GlobalVariable.h" export * }
   module IR_NoFolder { header "IR/NoFolder.h" export * }
   module IR_Module { header "IR/Module.h" export * }
   module IR_ModuleSummaryIndex { header "IR/ModuleSummaryIndex.h" export * }
   module IR_ModuleSummaryIndexYAML { header "IR/ModuleSummaryIndexYAML.h" export * }
   module IR_Function { header "IR/Function.h" export * }
module LLVM_intrinsic_gen {
   module Analysis_PostDominators { header "Analysis/PostDominators.h" export * }
   module IR_DomTreeUpdater { header "IR/DomTreeUpdater.h" export * }
   module IR_IRBuilder { header "IR/IRBuilder.h" export * }
   module IR_PassManager { header "IR/PassManager.h" export * }
   module IR_PredIteratorCache { header "IR/PredIteratorCache.h" export * }
   module IR_Verifier { header "IR/Verifier.h" export * }
   module IR_InstIterator { header "IR/InstIterator.h" export * }
   module IR_InstVisitor { header "IR/InstVisitor.h" export * }
-  module IR_Intrinsics { header "IR/Intrinsics.h" export * }
+  module IR_Intrinsics {
+    header "IR/Intrinsics.h"
+    extern module LLVM_Extern_IR_Intricsics_Gen "module.extern.modulemap"
+    extern module LLVM_Extern_IR_Intrinsics_Enum "module.extern.modulemap"
+    export *
+  }
   module IR_IntrinsicInst { header "IR/IntrinsicInst.h" export * }
   module IR_PatternMatch { header "IR/PatternMatch.h" export * }
   module IR_Statepoint { header "IR/Statepoint.h" export * }
 
   export *
 }
 
 module LLVM_IR {

 module LLVM_TableGen { requires cplusplus umbrella "TableGen" module * { export * } }
 
 module LLVM_Transforms {
   requires cplusplus
   umbrella "Transforms"
   module * { export * }
 }
 
+extern module LLVM_Extern_Utils_DataTypes "module.extern.modulemap"
+
 // A module covering ADT/ and Support/. These are intertwined and
 // codependent, and notionally form a single module.
 module LLVM_Utils {
   module ADT {
     requires cplusplus
 
     umbrella "ADT"
     module * { export * }