Merge pull request swiftlang#35779 from nathawes/driver-vfs-source-files

[Driver] Don't check input file existence if a -vfsoverlay arg is present.

Author: Nathan Hawes

lib/Driver/Driver.cpp

@@ -1284,6 +1284,7 @@ void Driver::buildInputs(const ToolChain &TC,
                          const DerivedArgList &Args,
                          InputFileList &Inputs) const {
   llvm::DenseMap<StringRef, StringRef> SourceFileNames;
+  bool HasVFS = Args.hasArg(options::OPT_vfsoverlay);
 
   for (Arg *A : Args) {
     if (A->getOption().getKind() == Option::InputClass) {
@@ -1305,7 +1306,7 @@ void Driver::buildInputs(const ToolChain &TC,
         }
       }
 
-      if (checkInputExistence(*this, Args, Diags, Value))
+      if (HasVFS || checkInputExistence(*this, Args, Diags, Value))
         Inputs.push_back(std::make_pair(Ty, A));
 
       if (Ty == file_types::TY_Swift) {

test/Driver/vfs.swift

@@ -7,3 +7,7 @@
 // RUN: %swiftc_driver -driver-print-jobs -c -vfsoverlay overlay1.yaml -vfsoverlay overlay2.yaml -vfsoverlay overlay3.yaml %s | %FileCheck --check-prefix=CHECK-MULTIPLE %s
 
 // CHECK-MULTIPLE: bin{{/|\\\\}}swift{{(-frontend|c)?(\.exe)?"?}} -frontend{{.*}}-c{{.*}}-vfsoverlay overlay1.yaml -vfsoverlay overlay2.yaml -vfsoverlay overlay3.yaml
+
+// Verifies that input paths are not rejected prematurely when -vfsoverlay is present as they may exist on the vfs (which the frontend accounts for) even if they don't exist on the real file system.
+// RUN: not %swiftc_driver -driver-print-jobs -c %t/file-not-on-the-real-filesystem.swift
+// RUN: %swiftc_driver -driver-print-jobs -c -vfsoverlay overlay1.yaml %t/file-not-on-the-real-filesystem.swift