[Frontend] Recover missing input file by dummy input buffer.

include/swift/Frontend/Frontend.h

@@ -572,7 +572,9 @@ class CompilerInstance {
   /// Return the buffer ID if it is not already compiled, or None if so.
   /// Set failed on failure.
 
-  Optional<unsigned> getRecordedBufferID(const InputFile &input, bool &failed);
+  Optional<unsigned> getRecordedBufferID(const InputFile &input,
+                                         const bool shouldRecover,
+                                         bool &failed);
 
   /// Given an input file, return a buffer to use for its contents,
   /// and a buffer for the corresponding module doc file if one exists.

include/swift/Frontend/FrontendInputsAndOutputs.h

@@ -46,6 +46,9 @@ class FrontendInputsAndOutputs {
   /// Punt where needed to enable batch mode experiments.
   bool AreBatchModeChecksBypassed = false;
 
+  /// Recover missing inputs. Note that recovery itself is users responsibility.
+  bool ShouldRecoverMissingInputs = false;
+
 public:
   bool areBatchModeChecksBypassed() const { return AreBatchModeChecksBypassed; }
   void setBypassBatchModeChecks(bool bbc) { AreBatchModeChecksBypassed = bbc; }
@@ -66,6 +69,9 @@ class FrontendInputsAndOutputs {
 
   bool isWholeModule() const { return !hasPrimaryInputs(); }
 
+  bool shouldRecoverMissingInputs() { return ShouldRecoverMissingInputs; }
+  void setShouldRecoverMissingInputs() { ShouldRecoverMissingInputs = true; }
+
   // Readers:
 
   // All inputs:

lib/Frontend/Frontend.cpp

@@ -599,17 +599,23 @@ bool CompilerInstance::setUpInputs() {
 
   const auto &Inputs =
       Invocation.getFrontendOptions().InputsAndOutputs.getAllInputs();
+  const bool shouldRecover = Invocation.getFrontendOptions()
+                                 .InputsAndOutputs.shouldRecoverMissingInputs();
+
+  bool hasFailed = false;
   for (const InputFile &input : Inputs) {
     bool failed = false;
-    Optional<unsigned> bufferID = getRecordedBufferID(input, failed);
-    if (failed)
-      return true;
+    Optional<unsigned> bufferID =
+        getRecordedBufferID(input, shouldRecover, failed);
+    hasFailed |= failed;
 
     if (!bufferID.hasValue() || !input.isPrimary())
       continue;
 
     recordPrimaryInputBuffer(*bufferID);
   }
+  if (hasFailed)
+    return true;
 
   // Set the primary file to the code-completion point if one exists.
   if (codeCompletionBufferID.hasValue() &&
@@ -621,8 +627,9 @@ bool CompilerInstance::setUpInputs() {
   return false;
 }
 
-Optional<unsigned> CompilerInstance::getRecordedBufferID(const InputFile &input,
-                                                         bool &failed) {
+Optional<unsigned>
+CompilerInstance::getRecordedBufferID(const InputFile &input,
+                                      const bool shouldRecover, bool &failed) {
   if (!input.getBuffer()) {
     if (Optional<unsigned> existingBufferID =
             SourceMgr.getIDForBufferIdentifier(input.getFileName())) {
@@ -631,6 +638,13 @@ Optional<unsigned> CompilerInstance::getRecordedBufferID(const InputFile &input,
   }
   auto buffers = getInputBuffersIfPresent(input);
 
+  // Recover by dummy buffer if requested.
+  if (!buffers.hasValue() && shouldRecover &&
+      input.getType() == file_types::TY_Swift && !input.isPrimary()) {
+    buffers = ModuleBuffers(llvm::MemoryBuffer::getMemBuffer(
+        "// missing file\n", input.getFileName()));
+  }
+
   if (!buffers.hasValue()) {
     failed = true;
     return None;

lib/Frontend/FrontendInputsAndOutputs.cpp

@@ -38,6 +38,7 @@ FrontendInputsAndOutputs::FrontendInputsAndOutputs(
   for (InputFile input : other.AllInputs)
     addInput(input);
   IsSingleThreadedWMO = other.IsSingleThreadedWMO;
+  ShouldRecoverMissingInputs = other.ShouldRecoverMissingInputs;
 }
 
 FrontendInputsAndOutputs &FrontendInputsAndOutputs::
@@ -46,6 +47,7 @@ operator=(const FrontendInputsAndOutputs &other) {
   for (InputFile input : other.AllInputs)
     addInput(input);
   IsSingleThreadedWMO = other.IsSingleThreadedWMO;
+  ShouldRecoverMissingInputs = other.ShouldRecoverMissingInputs;
   return *this;
 }
 

lib/IDE/Utils.cpp

@@ -215,6 +215,7 @@ static FrontendInputsAndOutputs resolveSymbolicLinksInInputs(
       ++primaryCount;
     }
     assert(primaryCount < 2 && "cannot handle multiple primaries");
+
     replacementInputsAndOutputs.addInput(
         InputFile(newFilename.str(), newIsPrimary, input.getBuffer()));
   }
@@ -310,6 +311,11 @@ bool ide::initCompilerInvocation(
       resolveSymbolicLinksInInputs(
           Invocation.getFrontendOptions().InputsAndOutputs,
           UnresolvedPrimaryFile, FileSystem, Error);
+
+  // SourceKit functionalities want to proceed even if there are missing inputs.
+  Invocation.getFrontendOptions().InputsAndOutputs
+      .setShouldRecoverMissingInputs();
+
   if (!Error.empty())
     return true;
 

test/Frontend/missing_files.swift

@@ -0,0 +1,17 @@
+// RUN: %empty-directory(%t)
+
+// RUN: not %target-swift-frontend -c -parse-as-library /tmp/SOMETHING_DOES_NOT_EXIST_1.swift -primary-file %s /tmp/SOMETHING_DOES_NOT_EXIST_2.swift -o %t/out.o 2> %t/error1.output
+// RUN: not test -f %t/out.o
+// RUN: %FileCheck %s -input-file %t/error1.output --check-prefixes=CHECK
+
+// RUN: not %target-swift-frontend -c -parse-as-library -primary-file /tmp/SOMETHING_DOES_NOT_EXIST_1.swift -primary-file %s /tmp/SOMETHING_DOES_NOT_EXIST_2.swift -o %t/out1.o -o %t/out2.o 2> %t/error2.output
+// RUN: not test -f %t/out1.o
+// RUN: not test -f %t/out2.o
+// RUN: %FileCheck %s -input-file %t/error2.output --check-prefixes=CHECK
+
+// CHECK-DAG: <unknown>:0: error: error opening input file '{{[/\\]}}tmp{{[/\\]}}SOMETHING_DOES_NOT_EXIST_1.swift' ({{.*}})
+// CHECK-DAG: <unknown>:0: error: error opening input file '{{[/\\]}}tmp{{[/\\]}}SOMETHING_DOES_NOT_EXIST_2.swift' ({{.*}})
+
+public var x = INVALID_DECL
+// CHECK-NOT: INVALID_DECL
+

test/SourceKit/CodeComplete/complete_missing_files.swift

@@ -0,0 +1,3 @@
+// RUN: %sourcekitd-test -req=complete -pos=1:1 %s -- /tmp/SOMETHING_DOES_NOT_EXIST_1.swift %s /tmp/SOMETHING_DOES_NOT_EXIST_2.swift | %FileCheck %s
+
+// CHECK: results: [