Make KDoc generate documentation on red code

KDoc is not a compiler, so it should not care whether or not the code is valid.
Therefore suppress the compiler's exit code, errors and warnings in KDoc plugin

libraries/tools/kdoc-maven-plugin/src/main/java/org/jetbrains/kotlin/maven/doc/KDocMojo.java

@@ -17,8 +17,11 @@
 package org.jetbrains.kotlin.maven.doc;
 
 import org.apache.maven.plugin.MojoExecutionException;
+import org.jetbrains.jet.cli.common.CLICompiler;
+import org.jetbrains.jet.cli.common.ExitCode;
 import org.jetbrains.jet.cli.common.arguments.CommonCompilerArguments;
 import org.jetbrains.jet.cli.common.arguments.K2JVMCompilerArguments;
+import org.jetbrains.jet.cli.common.messages.MessageCollector;
 import org.jetbrains.jet.cli.jvm.K2JVMCompiler;
 import org.jetbrains.kotlin.doc.KDocArguments;
 import org.jetbrains.kotlin.doc.KDocCompiler;
@@ -183,6 +186,21 @@ public class KDocMojo extends KotlinCompileMojoBase {
         return new KDocArguments();
     }
 
+    @Override
+    protected ExitCode executeCompiler(
+            CLICompiler compiler,
+            CommonCompilerArguments arguments,
+            MessageCollector messageCollector
+    ) {
+        ExitCode exitCode = super.executeCompiler(compiler, arguments, messageCollector);
+        if (exitCode == ExitCode.COMPILATION_ERROR) {
+            // KDoc should ignore compilation errors, since it's not supposed to compile code.
+            // KDoc is supposed to generate documentation by the code that may be correct or not
+            return ExitCode.OK;
+        }
+        return exitCode;
+    }
+
     @Override
     protected void configureCompilerArguments(CommonCompilerArguments arguments) throws MojoExecutionException {
         if (arguments instanceof K2JVMCompilerArguments) {

libraries/tools/kdoc/src/main/kotlin/org/jetbrains/kotlin/doc/KDocCompiler.kt

@@ -6,6 +6,7 @@ import org.jetbrains.jet.cli.common.CLIConfigurationKeys
 import org.jetbrains.jet.cli.common.arguments.K2JVMCompilerArguments;
 import org.jetbrains.jet.cli.jvm.K2JVMCompiler
 import org.jetbrains.jet.config.CompilerConfiguration
+import org.jetbrains.jet.cli.common.messages.MessageCollector
 
 /**
 * Main for running the KDocCompiler
@@ -23,6 +24,9 @@ class KDocCompiler() : K2JVMCompiler() {
     protected override fun configureEnvironment(configuration : CompilerConfiguration, arguments : K2JVMCompilerArguments) {
         super.configureEnvironment(configuration, arguments)
         configuration.add(CLIConfigurationKeys.COMPILER_PLUGINS, KDoc(arguments as KDocArguments))
+
+        // Suppress all messages from the compiler, because KDoc is not a compiler
+        configuration.put(CLIConfigurationKeys.MESSAGE_COLLECTOR_KEY, MessageCollector.NONE)
     }
 
     protected override fun createArguments() : K2JVMCompilerArguments {

libraries/tools/kotlin-maven-plugin/src/main/java/org/jetbrains/kotlin/maven/KotlinCompileMojoBase.java

@@ -206,7 +206,7 @@ public abstract class KotlinCompileMojoBase extends AbstractMojo {
             }
         };
 
-        final ExitCode exitCode = compiler.exec(messageCollector, arguments);
+        final ExitCode exitCode = executeCompiler(compiler, arguments, messageCollector);
 
         switch (exitCode) {
             case COMPILATION_ERROR:
@@ -258,6 +258,15 @@ public abstract class KotlinCompileMojoBase extends AbstractMojo {
         return new K2JVMCompilerArguments();
     }
 
+    @NotNull
+    protected ExitCode executeCompiler(
+            @NotNull CLICompiler compiler,
+            @NotNull CommonCompilerArguments arguments,
+            @NotNull MessageCollector messageCollector
+    ) {
+        return compiler.exec(messageCollector, arguments);
+    }
+
     /**
      * Derived classes can register custom plugins or configurations
      */