[Explicit Module Builds] Switch versioned 'canImport' to return 'true' when encountering unversioned candidate

Specifically, when the scanner found a candidate which does not carry a user-specified version, it will pass '-module-can-import Foo' to compilation. During compilation, if the check is versioned but the candidate is unversioned, evaluate the check to 'true' to restore the behavior we had with implicitly-built modules.

Resolves rdar://148134993

include/swift/AST/ASTContext.h

@@ -1184,7 +1184,7 @@ public:
   /// module is loaded in full.
   bool canImportModuleImpl(ImportPath::Module ModulePath, SourceLoc loc,
                            llvm::VersionTuple version, bool underlyingVersion,
-                           bool updateFailingList,
+                           bool isSourceCanImport,
                            llvm::VersionTuple &foundVersion) const;
 
   /// Add successful canImport modules.

lib/AST/ASTContext.cpp

@@ -2674,7 +2674,7 @@ void ASTContext::addSucceededCanImportModule(
 bool ASTContext::canImportModuleImpl(ImportPath::Module ModuleName,
                                      SourceLoc loc, llvm::VersionTuple version,
                                      bool underlyingVersion,
-                                     bool updateFailingList,
+                                     bool isSourceCanImport,
                                      llvm::VersionTuple &foundVersion) const {
   SmallString<64> FullModuleName;
   ModuleName.getString(FullModuleName);
@@ -2692,21 +2692,14 @@ bool ASTContext::canImportModuleImpl(ImportPath::Module ModuleName,
     if (version.empty())
       return true;
 
-    if (underlyingVersion) {
-      if (!Found->second.UnderlyingVersion.empty())
-        return version <= Found->second.UnderlyingVersion;
-    } else {
-      if (!Found->second.Version.empty())
-        return version <= Found->second.Version;
-    }
-
-    // If the canImport information is coming from the command-line, then no
-    // need to continue the search, return false. For checking modules that are
-    // not passed from command-line, allow fallback to the module loading since
-    // this is not in a canImport request context that has already been resolved
-    // by scanner.
-    if (!SearchPathOpts.CanImportModuleInfo.empty())
-      return false;
+    if (underlyingVersion)
+      return Found->second.UnderlyingVersion.empty()
+                 ? true
+                 : version <= Found->second.UnderlyingVersion;
+    else
+      return Found->second.Version.empty()
+                 ? true
+                 : version <= Found->second.Version;
   }
 
   if (version.empty()) {
@@ -2720,7 +2713,7 @@ bool ASTContext::canImportModuleImpl(ImportPath::Module ModuleName,
         return true;
     }
 
-    if (updateFailingList)
+    if (isSourceCanImport)
       FailedModuleImportNames.insert(ModuleNameStr);
 
     return false;

test/Parse/ConditionalCompilation/can_import_options.swift

@@ -73,8 +73,8 @@ func canImportVersioned() {
 #endif
 
 #if canImport(Bar, _underlyingVersion: 113.33)
-  // Bar is a Swift module with no underlying clang module.
-  let underlyingMinorSmaller = 1
+  // Bar is an unversioned Swift module with no underlying clang module.
+  let underlyingMinorSmaller = 1 // expected-warning {{initialization of immutable value 'underlyingMinorSmaller' was never used; consider replacing with assignment to '_' or removing it}}
 #endif
 
 #if canImport(Bar)

test/Parse/ConditionalCompilation/can_import_version.swift

@@ -68,8 +68,8 @@ func canImportVersioned() {
 #endif
 
 #if canImport(Foo, _underlyingVersion: 113.33)
-  // Foo is a Swift module with no underlying clang module.
-  let underlyingMinorSmaller = 1
+  // Foo is an unversioned Swift module with no underlying clang module.
+  let underlyingMinorSmaller = 1 // expected-warning {{initialization of immutable value 'underlyingMinorSmaller' was never used; consider replacing with assignment to '_' or removing it}}
 #endif
 
 #if canImport(Foo)
@@ -136,7 +136,7 @@ func canImportVersionedString() {
 #endif
 
 #if canImport(Foo, _underlyingVersion: "113.33")
-  // Foo is a Swift module with no underlying clang module.
-  let underlyingMinorSmaller = 1
+  // Foo is an unversioned Swift module with no underlying clang module.
+  let underlyingMinorSmaller = 1 // expected-warning {{initialization of immutable value 'underlyingMinorSmaller' was never used; consider replacing with assignment to '_' or removing it}}
 #endif
 }

test/ScanDependencies/can_import_explicit_versioned_unversioned_module.swift

@@ -0,0 +1,58 @@
+// REQUIRES: executable_test
+// RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/inputs)
+// RUN: %empty-directory(%t/module-cache)
+// RUN: split-file %s %t
+
+// - Fixup the input module file map
+// RUN: sed -e "s|INPUTSDIR|%/t/inputs|g" %t/map.json.template > %t/map.json.template1
+// RUN: sed -e "s|STDLIBMOD|%/stdlib_module|g" %t/map.json.template1 > %t/map.json.template2
+// RUN: sed -e "s|ONONEMOD|%/ononesupport_module|g" %t/map.json.template2 > %t/map.json.template3
+// RUN: sed -e "s|MYLIBMOD|%/t/inputs/MyLib.swiftmodule|g" %t/map.json.template3 > %t/map.json.template4
+// RUN: sed -e "s|SWIFTLIBDIR|%swift-lib-dir|g" %t/map.json.template4 > %t/map.json
+
+// - Set up explicit dependencies for MyExe
+// RUN: %target-swift-emit-pcm -module-name SwiftShims %swift-lib-dir/swift/shims/module.modulemap -o %t/inputs/SwiftShims.pcm
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/inputs/MyLib.swiftmodule %t/MyLib.swift -module-name MyLib -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -disable-implicit-swift-modules -explicit-swift-module-map-file %t/map.json
+
+// - Build MyExe
+// RUN: %target-swift-frontend -c %t/MyExe.swift -I %t/inputs -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import -disable-implicit-swift-modules -explicit-swift-module-map-file %t/map.json -module-can-import MyLib -verify 
+
+//--- map.json.template
+[
+  {
+      "moduleName": "Swift",
+      "modulePath": "STDLIBMOD",
+      "isFramework": false
+  },
+  {
+      "moduleName": "SwiftOnoneSupport",
+      "modulePath": "ONONEMOD",
+      "isFramework": false
+  },
+  {
+      "moduleName": "SwiftShims",
+      "isFramework": false,
+      "clangModuleMapPath": "SWIFTLIBDIR/swift/shims/module.modulemap",
+      "clangModulePath": "INPUTSDIR/SwiftShims.pcm"
+  },
+  {
+      "moduleName": "MyLib",
+      "modulePath": "MYLIBMOD",
+      "isFramework": false
+  }  
+]
+
+//--- MyLib.swift
+public func Foo() {
+    print("foo")
+}
+
+//--- MyExe.swift
+#if canImport(MyLib, _version: 42)
+  #warning("versioned canImport() of unversioned module is working")
+// expected-warning@-1{{versioned canImport() of unversioned module is working}}
+#else
+  #warning("versioned canImport() of unversioned module is broken")
+#endif
+  

test/ScanDependencies/module_deps_can_import.swift

@@ -1,6 +1,10 @@
 // RUN: %empty-directory(%t)
+// RUN: %empty-directory(%t/unversionedInputs)
 // RUN: split-file %s %t
-// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %t/main.swift -module-name Test -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %t/include -swift-version 4
+
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/unversionedUnputs/Foo.swiftmodule %t/Foo.swift -module-name Foo -disable-implicit-concurrency-module-import -disable-implicit-string-processing-module-import
+
+// RUN: %target-swift-frontend -scan-dependencies -module-cache-path %t/clang-module-cache %t/main.swift -module-name Test -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -I %t/include -I %t/unversionedUnputs
 
 // RUN: %{python} %S/../CAS/Inputs/SwiftDepsExtractor.py %t/deps.json Test directDependencies | %FileCheck %s
 
@@ -17,13 +21,24 @@
 // CMD-NEXT: "ClangTest.Sub"
 // CMD-NEXT: "-module-can-import"
 // CMD-NEXT: "F"
+// CMD-NEXT: "-module-can-import"
+// CMD-NEXT: "Foo"
 // CMD-NEXT: "-module-can-import-version"
 // CMD-NEXT: "Version"
 // CMD-NEXT: "100.1"
 // CMD-NEXT: "0"
 
+//--- Foo.swift
+public func Foo() {
+    print("foo")
+}
+
 //--- main.swift
 
+#if canImport(Foo, _version: 44)
+import Foo
+#endif
+
 #if canImport(Missing)
 import G
 #endif