[libcxx-commits] [libcxx] [libc++] Reformulate availability in terms of LLVM releases (PR #87563)

[Mark de Wever via libcxx-commits]

================
@@ -28,30 +28,32 @@
 // that previously released library. Normally, this would be a load-time error
 // when one tries to launch the program against the older library.
 //
-// For example, the filesystem library was introduced in the dylib in macOS 10.15.
-// If a user compiles on a macOS 10.15 host but targets macOS 10.13 with their
-// program, the compiler would normally not complain (because the required
-// declarations are in the headers), but the dynamic loader would fail to find
-// the symbols when actually trying to launch the program on macOS 10.13. To
-// turn this into a compile-time issue instead, declarations are annotated with
-// when they were introduced, and the compiler can produce a diagnostic if the
-// program references something that isn't available on the deployment target.
+// For example, the filesystem library was introduced in the dylib in LLVM 9.
+// On Apple platforms, this corresponds to macOS 10.15. If a user compiles on
+// a macOS 10.15 host but targets macOS 10.13 with their program, the compiler
+// would normally not complain (because the required declarations are in the
+// headers), but the dynamic loader would fail to find the symbols when actually
+// trying to launch the program on macOS 10.13. To turn this into a compile-time
+// issue instead, declarations are annotated with when they were introduced, and
+// the compiler can produce a diagnostic if the program references something that
+// isn't available on the deployment target.
 //
 // This mechanism is general in nature, and any vendor can add their markup to
 // the library (see below). Whenever a new feature is added that requires support
 // in the shared library, two macros are added below to allow marking the feature
 // as unavailable:
-// 1. A macro named `_LIBCPP_AVAILABILITY_HAS_NO_<feature>` which must be defined
-//    exactly when compiling for a target that doesn't support the feature.
-// 2. A macro named `_LIBCPP_AVAILABILITY_<feature>`, which must always be defined
-//    and must expand to the proper availability attribute for the platform.
+// 1. A macro named `_LIBCPP_AVAILABILITY_HAS_<feature>` which must be defined
+//    to `_LIBCPP_INTRODUCED_IN_<version>` for the appropriate LLVM version.
+// 2. A macro named `_LIBCPP_AVAILABILITY_<feature>`, which must be defined to
+//    `_LIBCPP_INTRODUCED_IN_<version>_MARKUP` for the appropriate LLVM version.
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mordante wrote:

Do you want to change this?

https://github.com/llvm/llvm-project/pull/87563