[Batch Mode] Add frontend check to ensure that all primaries are present in the supplementary output filemap.

include/swift/AST/DiagnosticsFrontend.def

@@ -136,6 +136,9 @@ ERROR(error_underlying_module_not_found,none,
 ERROR(error_unable_to_load_supplementary_output_file_map, none,
       "unable to load supplementary output file map '%0': %1", (StringRef, StringRef))
 
+ERROR(error_missing_entry_in_supplementary_output_file_map, none,
+      "supplementary output file map '%0' is missing an entry for '%1' (this likely indicates a compiler issue; please file a bug report)", (StringRef, StringRef))
+
 ERROR(error_repl_requires_no_input_files,none,
   "REPL mode requires no input files", ())
 ERROR(error_mode_requires_one_input_file,none,

include/swift/Frontend/ArgsToFrontendOutputsConverter.h

@@ -24,6 +24,7 @@
 #include <vector>
 
 namespace swift {
+class OutputFileMap;
 
 /// Given the command line arguments and information about the inputs,
 /// Fill in all the information in FrontendInputsAndOutputs.

lib/Frontend/ArgsToFrontendOutputsConverter.cpp

@@ -518,13 +518,23 @@ SupplementaryOutputPathsComputer::readSupplementaryOutputFileMap() const {
   }
 
   std::vector<SupplementaryOutputPaths> outputPaths;
+  bool hadError = false;
   InputsAndOutputs.forEachInputProducingSupplementaryOutput(
       [&](const InputFile &input) -> bool {
         const TypeToPathMap *mapForInput =
             OFM->getOutputMapForInput(input.file());
+        if (!mapForInput) {
+          Diags.diagnose(
+              SourceLoc(),
+              diag::error_missing_entry_in_supplementary_output_file_map,
+              supplementaryFileMapPath, input.file());
+          hadError = true;
+        }
         outputPaths.push_back(createFromTypeToPathMap(mapForInput));
         return false;
       });
+  if (hadError)
+    return None;
 
   return outputPaths;
 }

test/Frontend/Inputs/supplementary_output_filemap_missing_a_primary.yaml

@@ -0,0 +1,4 @@
+"main.swift":
+  object: "main.o"
+  dependencies: "main.d"
+  diagnostics: "main.dia"

test/Frontend/batch_mode_output_file_map_missing_primary.swift

@@ -0,0 +1,6 @@
+// RUN: %empty-directory(%t)
+// RUN: echo 'print("Hello, World!")' >%t/main.swift
+// RUN: touch %t/file-01.swift
+// RUN: (cd %t && not %target-swift-frontend -parse -primary-file main.swift -primary-file file-01.swift -supplementary-output-file-map %S/Inputs/supplementary_output_filemap_missing_a_primary.yaml >%t/errs.txt 2>&1)
+// RUN: %FileCheck %s <%t/errs.txt
+// CHECK: error: supplementary output file map '{{.*}}supplementary_output_filemap_missing_a_primary.yaml' is missing an entry for 'file-01.swift' (this likely indicates a compiler issue; please file a bug report)