Allow the compiler tag to be overridden and used for --version

Rather than showing the Swift/LLVM hashes for `--version`, allow a tag
to be specified (`SWIFT_TOOLCHAIN_VERSION`) that is then used instead.

Author: bnbarham

CMakeLists.txt

@@ -336,6 +336,8 @@ set(SWIFT_COMPILER_VERSION "" CACHE STRING
     "The internal version of the Swift compiler")
 set(CLANG_COMPILER_VERSION "" CACHE STRING
     "The internal version of the Clang compiler")
+set(SWIFT_TOOLCHAIN_VERSION "" CACHE STRING
+    "The Swift compiler tag")
 
 option(SWIFT_DISABLE_DEAD_STRIPPING
       "Turn off Darwin-specific dead stripping for Swift host tools." FALSE)

lib/Basic/CMakeLists.txt

@@ -134,10 +134,8 @@ if(NOT "${SWIFT_VENDOR}" STREQUAL "")
       " -DSWIFT_VENDOR=\"\\\"${SWIFT_VENDOR}\\\"\"")
 endif()
 
-set(SWIFT_COMPILER_VERSION "" CACHE STRING
-    "The string that identifies the SCM commit(s) for this build")
-
 message(STATUS "Swift compiler version: ${SWIFT_COMPILER_VERSION}")
+message(STATUS "Swift toolchain version: ${SWIFT_TOOLCHAIN_VERSION}")
 message(STATUS "Embedded clang compiler version: ${CLANG_COMPILER_VERSION}")
 
 if(SWIFT_COMPILER_VERSION)
@@ -150,3 +148,7 @@ if(CLANG_COMPILER_VERSION)
     " -DCLANG_COMPILER_VERSION=\"\\\"${CLANG_COMPILER_VERSION}\\\"\"")
 endif()
 
+if(SWIFT_TOOLCHAIN_VERSION)
+  set_property(SOURCE Version.cpp APPEND_STRING PROPERTY COMPILE_FLAGS
+    " -DSWIFT_TOOLCHAIN_VERSION=\"\\\"${SWIFT_TOOLCHAIN_VERSION}\\\"\"")
+endif()

lib/Basic/Version.cpp

@@ -50,21 +50,17 @@
 namespace swift {
 namespace version {
 
-/// Print a string of the form "LLVM xxxxx, Swift zzzzz", where each placeholder
+/// Print a string of the form "Swift xxxxx LLVM zzzzz", where each placeholder
 /// is the revision for the associated repository.
 static void printFullRevisionString(raw_ostream &out) {
   // Arbitrarily truncate to 15 characters. This should be enough to unique Git
   // hashes while keeping the REPL version string from overflowing 80 columns.
-#if defined(LLVM_REVISION)
-  out << "LLVM " << StringRef(LLVM_REVISION).slice(0, 15);
-# if defined(SWIFT_REVISION)
-  out << ", ";
-# endif
-#endif
-
 #if defined(SWIFT_REVISION)
   out << "Swift " << StringRef(SWIFT_REVISION).slice(0, 15);
 #endif
+#if defined(LLVM_REVISION)
+  out << " LLVM " << StringRef(LLVM_REVISION).slice(0, 15);
+#endif
 }
 
 Version Version::getCurrentLanguageVersion() {
@@ -270,15 +266,17 @@ std::string getSwiftFullVersion(Version effectiveVersion) {
 #endif
 
   OS << "Swift version " SWIFT_VERSION_STRING;
-#ifndef SWIFT_COMPILER_VERSION
+#if !defined(SWIFT_COMPILER_VERSION) && !defined(SWIFT_TOOLCHAIN_VERSION)
   OS << "-dev";
 #endif
 
   if (effectiveVersion != Version::getCurrentLanguageVersion()) {
     OS << " effective-" << effectiveVersion;
   }
 
-#if defined(SWIFT_COMPILER_VERSION)
+#if defined(SWIFT_TOOLCHAIN_VERSION)
+  OS << " (" SWIFT_TOOLCHAIN_VERSION ")";
+#elif defined(SWIFT_COMPILER_VERSION)
   OS << " (swiftlang-" SWIFT_COMPILER_VERSION;
 #if defined(CLANG_COMPILER_VERSION)
   OS << " clang-" CLANG_COMPILER_VERSION;