Support -Werror CLI argument to treat warnings as errors

The option is named "warningsAsErrors" in the Gradle plugin

 #KT-10563 Fixed

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/CommonToolArguments.kt

@@ -44,4 +44,8 @@ abstract class CommonToolArguments : Freezable(), Serializable {
     @GradleOption(DefaultValues.BooleanFalseDefault::class)
     @Argument(value = "-nowarn", description = "Generate no warnings")
     var suppressWarnings: Boolean by FreezableVar(false)
+
+    @GradleOption(DefaultValues.BooleanFalseDefault::class)
+    @Argument(value = "-Werror", description = "Report an error if there are any warnings")
+    var warningsAsErrors: Boolean by FreezableVar(false)
 }

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/messages/CompilerMessageSeverity.java

@@ -35,11 +35,14 @@ public enum CompilerMessageSeverity {
      */
     OUTPUT;
 
-    public static final EnumSet<CompilerMessageSeverity> ERRORS = EnumSet.of(ERROR, EXCEPTION);
     public static final EnumSet<CompilerMessageSeverity> VERBOSE = EnumSet.of(LOGGING);
 
     public boolean isError() {
-        return ERRORS.contains(this);
+        return this == EXCEPTION || this == ERROR;
+    }
+
+    public boolean isWarning() {
+        return this == STRONG_WARNING || this == WARNING;
     }
 
     @NotNull

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/messages/GroupingMessageCollector.java

@@ -24,16 +24,19 @@ import org.jetbrains.annotations.Nullable;
 
 import java.util.Comparator;
 import java.util.List;
+import java.util.Map;
 import java.util.Objects;
 
 public class GroupingMessageCollector implements MessageCollector {
     private final MessageCollector delegate;
+    private final boolean treatWarningsAsErrors;
 
     // Note that the key in this map can be null
     private final Multimap<CompilerMessageLocation, Message> groupedMessages = LinkedHashMultimap.create();
 
-    public GroupingMessageCollector(@NotNull MessageCollector delegate) {
+    public GroupingMessageCollector(@NotNull MessageCollector delegate, boolean treatWarningsAsErrors) {
         this.delegate = delegate;
+        this.treatWarningsAsErrors = treatWarningsAsErrors;
     }
 
     @Override
@@ -57,17 +60,29 @@ public class GroupingMessageCollector implements MessageCollector {
 
     @Override
     public boolean hasErrors() {
+        return hasExplicitErrors() || (treatWarningsAsErrors && hasWarnings());
+    }
+
+    private boolean hasExplicitErrors() {
         return groupedMessages.entries().stream().anyMatch(entry -> entry.getValue().severity.isError());
     }
 
+    private boolean hasWarnings() {
+        return groupedMessages.entries().stream().anyMatch(entry -> entry.getValue().severity.isWarning());
+    }
+
     public void flush() {
-        boolean hasErrors = hasErrors();
+        boolean hasExplicitErrors = hasExplicitErrors();
+
+        if (treatWarningsAsErrors && !hasExplicitErrors && hasWarnings()) {
+            report(CompilerMessageSeverity.ERROR, "warnings found and -Werror specified", null);
+        }
 
         List<CompilerMessageLocation> sortedKeys =
                 CollectionsKt.sortedWith(groupedMessages.keySet(), Comparator.nullsFirst(CompilerMessageLocationComparator.INSTANCE));
         for (CompilerMessageLocation location : sortedKeys) {
             for (Message message : groupedMessages.get(location)) {
-                if (!hasErrors || message.severity.isError() || message.severity == CompilerMessageSeverity.STRONG_WARNING) {
+                if (!hasExplicitErrors || message.severity.isError() || message.severity == CompilerMessageSeverity.STRONG_WARNING) {
                     delegate.report(message.severity, message.message, message.location);
                 }
             }