[Serialization] Fix message for using an older compiler's module file (#17340) (#17474)

Previously: "module compiled with Swift 4.1 cannot be imported in Swift
4.1.50" (i.e. following the -swift-version flag)

Now: "module compiled with Swift 4.1 cannot be imported by the Swift
4.2 compiler"

I'm pretty sure this is what I intended to do all along, and I just
messed it up when I originally implemented it. This is especially
important when working with downloadable toolchains, which would say
"module compiled with Swift 4.2 cannot be imported in Swift 4.1.50",
which is not really the problem at all. Now it'll fall back to the
more generic "module file was created by an older version of the
compiler" error.

(cherry picked from commit 2c40c6b)

Author: jrose-apple

include/swift/AST/DiagnosticsSema.def

@@ -575,7 +575,8 @@ ERROR(serialization_module_too_new,Fatal,
       "module file was created by a newer version of the compiler: %0",
       (StringRef))
 ERROR(serialization_module_language_version_mismatch,Fatal,
-      "module compiled with Swift %0 cannot be imported in Swift %1: %2",
+      "module compiled with Swift %0 cannot be imported by the Swift %1 "
+      "compiler: %2",
       (StringRef, StringRef, StringRef))
 ERROR(serialization_module_too_old,Fatal,
       "module file was created by an older version of the compiler; "

lib/Serialization/SerializedModuleLoader.cpp

@@ -27,6 +27,7 @@
 #include <system_error>
 
 using namespace swift;
+using swift::version::Version;
 
 namespace {
 using AccessPathElem = std::pair<Identifier, SourceLoc>;
@@ -240,7 +241,7 @@ FileUnit *SerializedModuleLoader::loadAST(
 
     SmallString<32> versionBuf;
     llvm::raw_svector_ostream versionString(versionBuf);
-    versionString << Ctx.LangOpts.EffectiveLanguageVersion;
+    versionString << Version::getCurrentLanguageVersion();
     if (versionString.str() == shortVersion)
       return false;
 

test/Serialization/version-mismatches.swift

@@ -1,25 +1,19 @@
 // RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-old/ -show-diagnostics-after-fatal 2>&1 | %FileCheck -check-prefix CHECK -check-prefix TOO-OLD %s
 // RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-new/ -show-diagnostics-after-fatal 2>&1 | %FileCheck -check-prefix CHECK -check-prefix TOO-NEW %s
 
-// RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-old-language/ -show-diagnostics-after-fatal 2>&1 | %FileCheck -check-prefix CHECK -check-prefix LANGUAGE %s
-// RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-new-language/ -show-diagnostics-after-fatal 2>&1 | %FileCheck -check-prefix CHECK -check-prefix LANGUAGE %s
-
 // Update this line when "-swift-version 3" is no longer supported.
-// RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-new-language/ -show-diagnostics-after-fatal -swift-version 3 2>&1 | %FileCheck -check-prefix CHECK -check-prefix LANGUAGE-3 %s
-// Update this line when "-swift-version 4" is no longer supported.
-// RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-new-language/ -show-diagnostics-after-fatal -swift-version 4 2>&1 | %FileCheck -check-prefix CHECK -check-prefix LANGUAGE-4 %s
+// RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-new-language/ -show-diagnostics-after-fatal -swift-version 3 2>&1 | %FileCheck -check-prefix CHECK -check-prefix LANGUAGE %s
+// RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-new-language/ -show-diagnostics-after-fatal -swift-version 4 2>&1 | %FileCheck -check-prefix CHECK -check-prefix LANGUAGE %s
+// RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-new-language/ -show-diagnostics-after-fatal -swift-version 5 2>&1 | %FileCheck -check-prefix CHECK -check-prefix LANGUAGE %s
+
+// RUN: not %target-swift-frontend %s -typecheck -I %S/Inputs/too-old-language/ -show-diagnostics-after-fatal 2>&1 | %FileCheck -check-prefix CHECK -check-prefix LANGUAGE %s
 
 import Library
 // TOO-OLD: :[[@LINE-1]]:8: error: module file was created by an older version of the compiler; rebuild 'Library' and try again: {{.*}}too-old/Library.swiftmodule{{$}}
 // TOO-NEW: :[[@LINE-2]]:8: error: module file was created by a newer version of the compiler: {{.*}}too-new/Library.swiftmodule{{$}}
 
-// Update this line when the default language version changes
-// LANGUAGE: :[[@LINE-5]]:8: error: module compiled with Swift X.Y cannot be imported in Swift {{.+}}.{{.+}}: {{.*}}too-{{old|new}}-language/Library.swiftmodule{{$}}
-
-// Update this line when "-swift-version 3" is no longer supported.
-// LANGUAGE-3: :[[@LINE-8]]:8: error: module compiled with Swift X.Y cannot be imported in Swift 3.{{.+}}: {{.*}}too-{{old|new}}-language/Library.swiftmodule{{$}}
-// Update this line when "-swift-version 3" is no longer supported.
-// LANGUAGE-4: :[[@LINE-10]]:8: error: module compiled with Swift X.Y cannot be imported in Swift 4.{{.+}}: {{.*}}too-{{old|new}}-language/Library.swiftmodule{{$}}
+// Update this line when the compiler version changes.
+// LANGUAGE: :[[@LINE-5]]:8: error: module compiled with Swift X.Y cannot be imported by the Swift 4.{{.+}} compiler: {{.*}}too-{{old|new}}-language/Library.swiftmodule{{$}}
 
 // Compiler thinks that the module is empty in all cases.
 // CHECK: :[[@LINE+1]]:1: error: module 'Library' has no member named 'foo'