Add ignoreAllWarnings API

New API on DiagnosticEngine to disable the reporting of warnings. No
tests currently, as this is not exposed upwards to any test-able
level, but tests will come when this is exposed e.g. through command
line arguments.

Author: milseman

include/swift/AST/DiagnosticEngine.h

@@ -398,6 +398,9 @@ namespace swift {
     /// fatal error
     bool showDiagnosticsAfterFatalError = false;
 
+    /// \brief Don't emit any warnings
+    bool ignoreAllWarnings = false;
+
     /// \brief Whether a fatal error has occurred
     bool fatalErrorOccurred = false;
 
@@ -420,6 +423,10 @@ namespace swift {
       showDiagnosticsAfterFatalError = val;
     }
 
+    /// \brief Whether to skip emitting warnings
+    void setIgnoreAllWarnings(bool val) { ignoreAllWarnings = val; }
+    bool getIgnoreAllWarnings() const { return ignoreAllWarnings; }
+
     void resetHadAnyError() {
       anyErrorOccurred = false;
       fatalErrorOccurred = false;
@@ -484,6 +491,12 @@ namespace swift {
       state.setShowDiagnosticsAfterFatalError(val);
     }
 
+    /// \brief Whether to skip emitting warnings
+    void setIgnoreAllWarnings(bool val) { state.setIgnoreAllWarnings(val); }
+    bool getIgnoreAllWarnings() const {
+      return state.getIgnoreAllWarnings();
+    }
+
     void resetHadAnyError() {
       state.resetHadAnyError();
     }

lib/AST/DiagnosticEngine.cpp

@@ -485,7 +485,7 @@ DiagnosticState::Behavior DiagnosticState::getBehavior(const Diagnostic &diag) {
   case DiagnosticKind::Error:
     return set(Behavior::Err);
   case DiagnosticKind::Warning:
-    return set(Behavior::Warn);
+    return set(ignoreAllWarnings ? Behavior::Ignore : Behavior::Warn);
   case DiagnosticKind::Note:
     return set(Behavior::Note);
   }