[CachedDiags] Don't cache diagnostics if command-line failed

Author: cachemeifyoucan

lib/FrontendTool/FrontendTool.cpp

@@ -2076,6 +2076,11 @@ int swift::performFrontend(ArrayRef<const char *> Args,
   auto finishDiagProcessing = [&](int retValue, bool verifierEnabled) -> int {
     FinishDiagProcessingCheckRAII.CalledFinishDiagProcessing = true;
     PDC.setSuppressOutput(false);
+    if (auto *CDP = Instance->getCachingDiagnosticsProcessor()) {
+      // Don't cache if build failed.
+      if (retValue)
+        CDP->endDiagnosticCapture();
+    }
     bool diagnosticsError = Instance->getDiags().finishProcessing();
     // If the verifier is enabled and did not encounter any verification errors,
     // return 0 even if the compile failed. This behavior isn't ideal, but large

test/CAS/loc-directive-diagnostics.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: not %target-swift-frontend -emit-module -emit-module-path %t/test.module \
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/test.module \
 // RUN:   -enable-cas -cas-path %t/cas -allow-unstable-cache-key-for-testing %s 2>&1 | %FileCheck %s
 // RUN: %cache-tool -cas-path %t/cas -cache-tool-action print-output-keys -- \
 // RUN:   %target-swift-frontend -emit-module -emit-module-path %t/test.module -enable-cas -cas-path %t/cas \
@@ -9,7 +9,7 @@
 // RUN:   -allow-unstable-cache-key-for-testing %s 2>&1 | %FileCheck %s
 
 #sourceLocation(file: "anything.swift", line: 1)
-func 1() {}
+#warning("this is a warning")
 #sourceLocation()
 
-// CHECK: anything.swift:1:6: error: function name
+// CHECK: anything.swift:1:10: warning: this is a warning