[ModuleInterface] Look for a prebuilt module by full target name

lib/Frontend/ParseableInterfaceModuleLoader.cpp

@@ -19,6 +19,7 @@
 #include "swift/AST/Module.h"
 #include "swift/AST/ProtocolConformance.h"
 #include "swift/Basic/Lazy.h"
+#include "swift/Basic/Platform.h"
 #include "swift/Basic/STLExtras.h"
 #include "swift/Frontend/Frontend.h"
 #include "swift/Frontend/ParseableInterfaceSupport.h"
@@ -826,7 +827,7 @@ class ParseableInterfaceModuleLoaderImpl {
     // Assemble the expected path: $PREBUILT_CACHE/Foo.swiftmodule or
     // $PREBUILT_CACHE/Foo.swiftmodule/arch.swiftmodule. Note that there's no
     // cache key here.
-    scratch.append(prebuiltCacheDir);
+    scratch = prebuiltCacheDir;
 
     // FIXME: Would it be possible to only have architecture-specific names
     // here? Then we could skip this check.
@@ -845,6 +846,48 @@ class ParseableInterfaceModuleLoaderImpl {
     return scratch.str();
   }
 
+  /// Hack to deal with build systems (including the Swift standard library, at
+  /// the time of this comment) that aren't yet using target-specific names for
+  /// multi-target swiftmodules, in case the prebuilt cache is.
+  Optional<StringRef>
+  computeFallbackPrebuiltModulePath(llvm::SmallString<256> &scratch) {
+    namespace path = llvm::sys::path;
+    StringRef sdkPath = ctx.SearchPathOpts.SDKPath;
+
+    // Check if the interface file comes from the SDK
+    if (sdkPath.empty() || !hasPrefix(path::begin(interfacePath),
+                                      path::end(interfacePath),
+                                      path::begin(sdkPath),
+                                      path::end(sdkPath)))
+      return None;
+
+    // If the module isn't target-specific, there's no fallback path.
+    StringRef inParentDirName =
+        path::filename(path::parent_path(interfacePath));
+    if (path::extension(inParentDirName) != ".swiftmodule")
+      return None;
+
+    // If the interface is already using the target-specific name, there's
+    // nothing else to try.
+    auto normalizedTarget = getTargetSpecificModuleTriple(ctx.LangOpts.Target);
+    if (path::stem(modulePath) == normalizedTarget.str())
+      return None;
+
+    // Assemble the expected path:
+    // $PREBUILT_CACHE/Foo.swiftmodule/target.swiftmodule. Note that there's no
+    // cache key here.
+    scratch = prebuiltCacheDir;
+    path::append(scratch, inParentDirName);
+    path::append(scratch, normalizedTarget.str());
+    scratch += ".swiftmodule";
+
+    // If there isn't a file at this location, skip returning a path.
+    if (!fs.exists(scratch))
+      return None;
+
+    return scratch.str();
+  }
+
   bool isInResourceDir(StringRef path) {
     StringRef resourceDir = ctx.SearchPathOpts.RuntimeLibraryPath;
     if (resourceDir.empty()) return false;
@@ -926,7 +969,12 @@ class ParseableInterfaceModuleLoaderImpl {
     if (!prebuiltCacheDir.empty()) {
       llvm::SmallString<256> scratch;
       std::unique_ptr<llvm::MemoryBuffer> moduleBuffer;
-      auto path = computePrebuiltModulePath(scratch);
+      Optional<StringRef> path = computePrebuiltModulePath(scratch);
+      if (!path) {
+        // Hack: deal with prebuilds of modules that still use the target-based
+        // names.
+        path = computeFallbackPrebuiltModulePath(scratch);
+      }
       if (path) {
         if (swiftModuleIsUpToDate(*path, deps, moduleBuffer)) {
           LLVM_DEBUG(llvm::dbgs() << "Found up-to-date prebuilt module at "

test/ParseableInterface/ModuleCache/prebuilt-module-cache-fallback.swift

@@ -0,0 +1,45 @@
+// Like prebuilt-module-cache-archs.swift, but testing the fallback behavior.
+// This means we have to know the expected names in advance, so this test only
+// runs on macOS.
+
+// REQUIRES: OS=macosx
+// REQUIRES: CPU=x86_64
+
+// Use the short name "x86_64.swiftmodule".
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/include/Lib.swiftmodule)
+// RUN: cp %S/Inputs/prebuilt-module-cache/Lib.swiftinterface %t/include/Lib.swiftmodule/x86_64.swiftinterface
+
+// Do a manual prebuild with the long name "x86_64-apple-macos.swiftmodule",
+// and see if it gets picked up.
+// RUN: %empty-directory(%t/MCP)
+// RUN: %empty-directory(%t/prebuilt-cache/Lib.swiftmodule)
+// RUN: sed -e 's/FromInterface/FromPrebuiltLong/g' %S/Inputs/prebuilt-module-cache/Lib.swiftinterface | %target-swift-frontend -parse-stdlib -module-cache-path %t/MCP -emit-module-path %t/prebuilt-cache/Lib.swiftmodule/x86_64-apple-macos.swiftmodule - -module-name Lib
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %t/include -I %t/include/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT-LONG %s
+// RUN: %{python} %S/Inputs/check-is-forwarding-module.py %t/MCP/Lib-*.swiftmodule
+
+// Prefer a matching name.
+// RUN: %empty-directory(%t/MCP)
+// RUN: sed -e 's/FromInterface/FromPrebuiltShort/g' %S/Inputs/prebuilt-module-cache/Lib.swiftinterface | %target-swift-frontend -parse-stdlib -module-cache-path %t/MCP -emit-module-path %t/prebuilt-cache/Lib.swiftmodule/x86_64.swiftmodule - -module-name Lib
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %t/include -I %t/include/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT-SHORT %s
+// RUN: %{python} %S/Inputs/check-is-forwarding-module.py %t/MCP/Lib-*.swiftmodule
+
+// Prefer a matching name in the other direction too.
+// RUN: %empty-directory(%t/MCP)
+// RUN: mv %t/include/Lib.swiftmodule/x86_64.swiftinterface %t/include/Lib.swiftmodule/x86_64-apple-macos.swiftinterface
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %t/include -I %t/include/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-PREBUILT-LONG %s
+// RUN: %{python} %S/Inputs/check-is-forwarding-module.py %t/MCP/Lib-*.swiftmodule
+
+// Don't do the fallback thing for long names to short names.
+// RUN: %empty-directory(%t/MCP)
+// RUN: rm %t/prebuilt-cache/Lib.swiftmodule/x86_64-apple-macos.swiftmodule
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-cache-path %t/MCP -sdk %t/include -I %t/include/ -prebuilt-module-cache-path %t/prebuilt-cache %s 2>&1 | %FileCheck -check-prefix=FROM-INTERFACE %s
+// RUN: not %{python} %S/Inputs/check-is-forwarding-module.py %t/MCP/Lib-*.swiftmodule
+
+import Lib
+
+struct X {}
+let _: X = Lib.testValue
+// FROM-INTERFACE: [[@LINE-1]]:16: error: cannot convert value of type 'FromInterface' to specified type 'X'
+// FROM-PREBUILT-LONG: [[@LINE-2]]:16: error: cannot convert value of type 'FromPrebuiltLong' to specified type 'X'
+// FROM-PREBUILT-SHORT: [[@LINE-3]]:16: error: cannot convert value of type 'FromPrebuiltShort' to specified type 'X'