[Clang][Modules] Support `requires cplusplus20` in a modulemap

[egorzhdan]

Summary

This change adds the support for requires cplusplus20 directive for a module declared in a Clang modulemap, similarly to existing directives requires cplusplus17, requires cplusplus14, etc.

rdar://108891417

[bruno]

LGTM

[egorzhdan]

@Bigcheese, @ChuanqiXu, could you please take a look at this patch?

[ChuanqiXu]

LGTM. Sorry for misleading.

[egorzhdan]

Looks like https://reviews.llvm.org/D150773 got there first.

clang/docs/Modules.rst

cplusplus11
   C++11 support is available.
 
 cplusplus14
   C++14 support is available.
 
 cplusplus17
   C++17 support is available.
 
+cplusplus20
+  C++20 support is available.
+
 c99
   C99 support is available.
 
 c11
   C11 support is available.
 
 c17
   C17 support is available.

clang/lib/Basic/Module.cpp

static bool hasFeature(StringRef Feature, const LangOptions &LangOpts,
   bool HasFeature = llvm::StringSwitch<bool>(Feature)
                         .Case("altivec", LangOpts.AltiVec)
                         .Case("blocks", LangOpts.Blocks)
                         .Case("coroutines", LangOpts.Coroutines)
                         .Case("cplusplus", LangOpts.CPlusPlus)
                         .Case("cplusplus11", LangOpts.CPlusPlus11)
                         .Case("cplusplus14", LangOpts.CPlusPlus14)
                         .Case("cplusplus17", LangOpts.CPlusPlus17)
+                        .Case("cplusplus20", LangOpts.CPlusPlus20)
                         .Case("c99", LangOpts.C99)
                         .Case("c11", LangOpts.C11)
                         .Case("c17", LangOpts.C17)
                         .Case("freestanding", LangOpts.Freestanding)
                         .Case("gnuinlineasm", LangOpts.GNUAsm)
                         .Case("objc", LangOpts.ObjC)
                         .Case("objc_arc", LangOpts.ObjCAutoRefCount)
                         .Case("opencl", LangOpts.OpenCL)

clang/test/Modules/Inputs/DependsOnModule.framework/module.map

explicit module CXX11 {
     requires cplusplus11
   }
   explicit module CXX14 {
     requires cplusplus14
   }
   explicit module CXX17 {
     requires cplusplus17
   }
+  explicit module CXX20 {
+    requires cplusplus20
+  }
   explicit module C99 {
     requires c99
   }
   explicit module C11 {
     requires c11
   }
   explicit module C17 {
     requires c17
   }
 }

clang/test/Modules/requires.m

 // [e-mail]:* {{module 'RequiresWithMissingHeader.HeaderAfter' requires feature 'missing'}}
 @import RequiresWithMissingHeader.HeaderAfter; // expected-note {{module imported here}}
 // [e-mail]/module.map:40 {{module 'DependsOnModule.CXX11' requires feature 'cplusplus11'}}
 @import DependsOnModule.CXX11; // expected-note {{module imported here}}
 // [e-mail]/module.map:43 {{module 'DependsOnModule.CXX14' requires feature 'cplusplus14'}}
 @import DependsOnModule.CXX14; // expected-note {{module imported here}}
 // [e-mail]/module.map:46 {{module 'DependsOnModule.CXX17' requires feature 'cplusplus17'}}
 @import DependsOnModule.CXX17; // expected-note {{module imported here}}
+// [e-mail]/module.map:49 {{module 'DependsOnModule.CXX20' requires feature 'cplusplus20'}}
+@import DependsOnModule.CXX20; // expected-note {{module imported here}}
 #else
-// [e-mail]/module.map:49 {{module 'DependsOnModule.C99' requires feature 'c99'}}
+// [e-mail]/module.map:52 {{module 'DependsOnModule.C99' requires feature 'c99'}}
 @import DependsOnModule.C99; // expected-note {{module imported here}}
-// [e-mail]/module.map:52 {{module 'DependsOnModule.C11' requires feature 'c11'}}
+// [e-mail]/module.map:55 {{module 'DependsOnModule.C11' requires feature 'c11'}}
 @import DependsOnModule.C11; // expected-note {{module imported here}}
-// [e-mail]/module.map:55 {{module 'DependsOnModule.C17' requires feature 'c17'}}
+// [e-mail]/module.map:58 {{module 'DependsOnModule.C17' requires feature 'c17'}}
 @import DependsOnModule.C17; // expected-note {{module imported here}}
 #endif