From 73cfe34622f54be665257ef80ce84769a95416db Mon Sep 17 00:00:00 2001
From: Keith Smiley <keithbsmiley@gmail.com>
Date: Fri, 22 Oct 2021 22:05:12 +0000
Subject: [PATCH] Allow -explicit-swift-module-map-file without full explicit
 module build

This enables the use of `-explicit-swift-module-map-file` for some
modules in the build, while still loading implicit modules as before.
This is useful to improve the performance of builds with many modules to
avoid searching many different directories pass with `-I`. Previously
VFS overlays could be used for this use case as well, but it seems
valuable to unify on the same infrastructure used for explicit module
builds.
---
 lib/Frontend/Frontend.cpp                     |  6 ++++--
 .../can_import_with_map_and_implicit.swift    | 21 +++++++++++++++++++
 2 files changed, 25 insertions(+), 2 deletions(-)
 create mode 100644 test/ScanDependencies/can_import_with_map_and_implicit.swift

diff --git a/lib/Frontend/Frontend.cpp b/lib/Frontend/Frontend.cpp
index dbd5bd03f51b5..961922d847f94 100644
--- a/lib/Frontend/Frontend.cpp
+++ b/lib/Frontend/Frontend.cpp
@@ -556,7 +556,7 @@ bool CompilerInstance::setUpModuleLoaders() {
   // If implicit modules are disabled, we need to install an explicit module
   // loader.
   bool ExplicitModuleBuild = Invocation.getFrontendOptions().DisableImplicitModules;
-  if (ExplicitModuleBuild) {
+  if (ExplicitModuleBuild || !Invocation.getSearchPathOptions().ExplicitSwiftModuleMap.empty()) {
     auto ESML = ExplicitSwiftModuleLoader::create(
         *Context,
         getDependencyTracker(), MLM,
@@ -564,7 +564,9 @@ bool CompilerInstance::setUpModuleLoaders() {
         IgnoreSourceInfoFile);
     this->DefaultSerializedLoader = ESML.get();
     Context->addModuleLoader(std::move(ESML));
-  } else {
+  }
+
+  if (!ExplicitModuleBuild) {
     if (MLM != ModuleLoadingMode::OnlySerialized) {
       // We only need ModuleInterfaceLoader for implicit modules.
       auto PIML = ModuleInterfaceLoader::create(
diff --git a/test/ScanDependencies/can_import_with_map_and_implicit.swift b/test/ScanDependencies/can_import_with_map_and_implicit.swift
new file mode 100644
index 0000000000000..509b33132881e
--- /dev/null
+++ b/test/ScanDependencies/can_import_with_map_and_implicit.swift
@@ -0,0 +1,21 @@
+// RUN: %empty-directory(%t)
+// RUN: mkdir -p %t/clang-module-cache
+// RUN: mkdir -p %t/inputs
+// RUN: mkdir -p %t/barinputs
+// RUN: echo "public func foo() {}" >> %t/foo.swift
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/inputs/Foo.swiftmodule -emit-module-doc-path %t/inputs/Foo.swiftdoc -emit-module-source-info -emit-module-source-info-path %t/inputs/Foo.swiftsourceinfo -module-cache-path %t.module-cache %t/foo.swift -module-name Foo
+// RUN: echo "public func bar() {}" >> %t/bar.swift
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/barinputs/Bar.swiftmodule -emit-module-doc-path %t/barinputs/Bar.swiftdoc -emit-module-source-info -emit-module-source-info-path %t/barinputs/Bar.swiftsourceinfo -module-cache-path %t.module-cache %t/bar.swift -module-name Bar
+
+// RUN: echo "[{" > %/t/inputs/map.json
+// RUN: echo "\"moduleName\": \"Foo\"," >> %/t/inputs/map.json
+// RUN: echo "\"modulePath\": \"%/t/inputs/Foo.swiftmodule\"," >> %/t/inputs/map.json
+// RUN: echo "\"docPath\": \"%/t/inputs/Foo.swiftdoc\"," >> %/t/inputs/map.json
+// RUN: echo "\"sourceInfoPath\": \"%/t/inputs/Foo.swiftsourceinfo\"," >> %/t/inputs/map.json
+// RUN: echo "\"isFramework\": false" >> %/t/inputs/map.json
+// RUN: echo "}]" >> %/t/inputs/map.json
+
+// RUN: not %target-swift-frontend -typecheck %s -explicit-swift-module-map-file %t/inputs/map.json -disable-implicit-swift-modules
+// RUN: %target-swift-frontend -typecheck %s -explicit-swift-module-map-file %t/inputs/map.json -I %t/barinputs
+import Foo
+import Bar