[Serialized diagnostics] Avoid generating filenames that break the reader

lib/Frontend/SerializedDiagnosticConsumer.cpp

@@ -225,6 +225,17 @@ namespace serialized_diagnostics {
 } // namespace serialized_diagnostics
 } // namespace swift
 
+/// Sanitize a filename for the purposes of the serialized diagnostics reader.
+static StringRef sanitizeFilename(
+    StringRef filename, SmallString<32> &scratch) {
+  if (!filename.endswith("/") && !filename.endswith("\\"))
+    return filename;
+
+  scratch = filename;
+  scratch += "_operator";
+  return scratch;
+}
+
 unsigned SerializedDiagnosticConsumer::getEmitFile(
     SourceManager &SM, StringRef Filename, unsigned bufferID
 ) {
@@ -248,9 +259,14 @@ unsigned SerializedDiagnosticConsumer::getEmitFile(
   Record.push_back(entry);
   Record.push_back(0); // For legacy.
   Record.push_back(0); // For legacy.
-  Record.push_back(Filename.size());
+
+  // Sanitize the filename enough that the serialized diagnostics reader won't
+  // reject it.
+  SmallString<32> filenameScratch;
+  auto sanitizedFilename = sanitizeFilename(Filename, filenameScratch);
+  Record.push_back(sanitizedFilename.size());
   State->Stream.EmitRecordWithBlob(State->Abbrevs.get(RECORD_FILENAME),
-                                   Record, Filename.data());
+                                   Record, sanitizedFilename.data());
 
   // If the buffer contains code that was synthesized by the compiler,
   // emit the contents of the buffer.

test/diagnostics/Inputs/slash.swift

@@ -0,0 +1,2 @@
+public func /(lhs: String, b: Int) -> Bool { false }
+

test/diagnostics/bad-generated-filenames.swift

@@ -0,0 +1,16 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -o %t/SlashA.swiftmodule %S/Inputs/slash.swift
+// RUN: %target-swift-frontend -emit-module -o %t/SlashB.swiftmodule %S/Inputs/slash.swift
+// RUN: not %target-swift-frontend -typecheck -I %t -serialize-diagnostics-path %t/serialized.dia %s
+// RUN: c-index-test -read-diagnostics %t/serialized.dia > %t/serialized.txt 2>&1
+// RUN: %FileCheck %s -check-prefix CHECK-DIA < %t/serialized.txt
+
+import SlashA
+import SlashB
+
+func test(a: String, b: Int) -> Bool {
+  // CHECK-DIA: [[@LINE+3]]:5: error: ambiguous use of operator '/'
+  // CHECK-DIA: SlashA./_operator
+  // CHECK-DIA: SlashB./_operator
+  a / b
+}