Swift: extract all source files in WMO mode

WMO stands for whole module optimization. It's a compilation mode where
all sources of a module are compiled together, e.g.
```
swift-frontend -emit-module A.swift B.swift -o Module.swiftmodule
```
This is opposed to incremental mode, where one would do something like
```
swift-frontend -emit-module -primary-file A.swift B.swift -module-name Module -o Module~A.swiftmodule
swift-frontend -emit-module A.swift -primary-file B.swift -module-name Module -o Module~B.swiftmodule
swift-frontend -merge-modules Module~A.swiftmodule Module~B.swiftmodule -o Module.swiftmodule
```

In WMO mode we were skipping extraction of all files after the first
one, because we were filtering in only files with an associated output,
and internally swift only assigns the output to the first input file in
WMO mode (which is just an implementation detail).

This patch refines that filter, by getting all input source files in
case there are no primary inputs.

Author: redsun82

swift/extractor/SwiftExtractor.cpp

@@ -161,11 +161,12 @@ static std::unordered_set<swift::ModuleDecl*> extractDeclarations(
 static std::unordered_set<std::string> collectInputFilenames(swift::CompilerInstance& compiler) {
   // The frontend can be called in many different ways.
   // At each invocation we only extract system and builtin modules and any input source files that
-  // have an output associated with them.
+  // are primary inputs, or all of them if there are no primary inputs (whole module optimization)
   std::unordered_set<std::string> sourceFiles;
-  auto inputFiles = compiler.getInvocation().getFrontendOptions().InputsAndOutputs.getAllInputs();
-  for (auto& input : inputFiles) {
-    if (input.getType() == swift::file_types::TY_Swift && !input.outputFilename().empty()) {
+  const auto& inOuts = compiler.getInvocation().getFrontendOptions().InputsAndOutputs;
+  for (auto& input : inOuts.getAllInputs()) {
+    if (input.getType() == swift::file_types::TY_Swift &&
+        (!inOuts.hasPrimaryInputs() || input.isPrimary())) {
       sourceFiles.insert(input.getFileName());
     }
   }
@@ -191,11 +192,15 @@ void codeql::extractSwiftFiles(SwiftExtractorState& state, swift::CompilerInstan
     todo.pop_back();
     bool isFromSourceFile = false;
     std::unordered_set<swift::ModuleDecl*> encounteredModules;
+    llvm::errs() << "MODULE: " << module->getRealName() << '\n';
     for (auto file : module->getFiles()) {
+      llvm::errs() << "  FILE: kind=" << static_cast<int>(file->getKind());
       auto sourceFile = llvm::dyn_cast<swift::SourceFile>(file);
       if (!sourceFile) {
+        llvm::errs() << '\n';
         continue;
       }
+      llvm::errs() << " name=" << sourceFile->getFilename() << '\n';
       isFromSourceFile = true;
       if (inputFiles.count(sourceFile->getFilename().str()) == 0) {
         continue;

swift/integration-tests/posix-only/frontend-invocations/Files.expected

@@ -6,6 +6,7 @@
 | F1.swift:0:0:0:0 | F1.swift |
 | F2.swift:0:0:0:0 | F2.swift |
 | F3.swift:0:0:0:0 | F3.swift |
+| F4.swift:0:0:0:0 | F4.swift |
 | F5.swift:0:0:0:0 | F5.swift |
 | G.swift:0:0:0:0 | G.swift |
 | H1.swift:0:0:0:0 | H1.swift |