[Caching] Fix versioned canImport check for swift module

Fix the ExplicitCASModuleLoader check for if `canImport` works for a
specific swift module. It was mistakenly using the clang caching schema
to load the underlying module but in reality, it should only load swift
module with swift caching schema.

In future, we should let dependency scanner to report version/underlying
version for the modules it enounters so the versioned canImport check
doesn't need to load and parse the module/TBD file to figure out if the
check is successful or not.

rdar://120554271

Author: cachemeifyoucan

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -22,6 +22,7 @@
 #include "swift/Basic/Platform.h"
 #include "swift/Basic/StringExtras.h"
 #include "swift/Frontend/CachingUtils.h"
+#include "swift/Frontend/CompileJobCacheResult.h"
 #include "swift/Frontend/Frontend.h"
 #include "swift/Frontend/ModuleInterfaceSupport.h"
 #include "swift/Parse/ParseVersion.h"
@@ -2446,12 +2447,19 @@ struct ExplicitCASModuleLoader::Implementation {
     if (!moduleRef)
       return nullptr;
 
-    clang::cas::CompileJobResultSchema schema(CAS);
+    auto proxy = CAS.getProxy(*moduleRef);
+    if (!proxy)
+      return proxy.takeError();
+
+    swift::cas::CompileJobResultSchema schema(CAS);
+    if (!schema.isRootNode(*proxy))
+      return nullptr;
+
     auto result = schema.load(*moduleRef);
     if (!result)
       return result.takeError();
-    auto output = result->getOutput(
-        clang::cas::CompileJobCacheResult::OutputKind::MainOutput);
+
+    auto output = result->getOutput(file_types::ID::TY_SwiftModuleFile);
     if (!output)
       return nullptr;
 

test/CAS/can-import.swift

@@ -14,6 +14,9 @@
 // RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json clang:B > %t/B.cmd
 // RUN: %swift_frontend_plain @%t/B.cmd
 
+// RUN: %{python} %S/Inputs/BuildCommandExtractor.py %t/deps.json C > %t/C.cmd
+// RUN: %swift_frontend_plain @%t/C.cmd
+
 // RUN: %{python} %S/Inputs/GenerateExplicitModuleMap.py %t/deps.json > %t/map.json
 // RUN: llvm-cas --cas %t/cas --make-blob --data %t/map.json > %t/map.casid
 
@@ -38,9 +41,18 @@ import A.Missing
 func b() {}
 #endif
 
+#if canImport(C, _version: 1.0)
+import C
+#endif
+
+#if canImport(C, _version: 2.0)
+import Missing
+#endif
+
 func useA() {
   a()
   b()
+  c()
 }
 
 //--- include/module.modulemap
@@ -61,3 +73,8 @@ void notused(void);
 
 //--- include/B.h
 void notused2(void);
+
+//--- include/C.swiftinterface
+// swift-interface-format-version: 1.0
+// swift-module-flags: -module-name C -O -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib -user-module-version 1.0
+public func c() { }