CLI: improve diagnostic message format

- render the whole line where the error/warning points to, if any, and another
  line with '^', like other compilers do
- lowercase diagnostic severity
- decapitalize the message if it doesn't start with a proper name

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/messages/CompilerMessageLocation.kt

@@ -21,15 +21,21 @@ import kotlin.platform.platformStatic
 public data class CompilerMessageLocation private constructor(
         public val path: String?,
         public val line: Int,
-        public val column: Int
+        public val column: Int,
+        public val lineContent: String?
 ) {
     override fun toString(): String =
             path + (if (line != -1 || column != -1) " (" + line + ":" + column + ")" else "")
 
     companion object {
-        public platformStatic val NO_LOCATION: CompilerMessageLocation = CompilerMessageLocation(null, -1, -1)
+        public platformStatic val NO_LOCATION: CompilerMessageLocation = CompilerMessageLocation(null, -1, -1, null)
 
-        public platformStatic fun create(path: String?, line: Int, column: Int): CompilerMessageLocation =
-                if (path == null) NO_LOCATION else CompilerMessageLocation(path, line, column)
+        public platformStatic fun create(
+                path: String?,
+                line: Int,
+                column: Int,
+                lineContent: String?
+        ): CompilerMessageLocation =
+                if (path == null) NO_LOCATION else CompilerMessageLocation(path, line, column, lineContent)
     }
 }

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

@@ -17,6 +17,8 @@
 package org.jetbrains.kotlin.cli.common.messages;
 
 import com.intellij.openapi.util.text.StringUtil;
+import com.intellij.util.LineSeparator;
+import kotlin.KotlinPackage;
 import kotlin.io.IoPackage;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
@@ -78,6 +80,8 @@ public interface MessageRenderer {
     };
 
     abstract class PlainText implements MessageRenderer {
+        private static final String LINE_SEPARATOR = LineSeparator.getSystemLineSeparator().getSeparatorString();
+
         @Override
         public String renderPreamble() {
             return "";
@@ -88,24 +92,56 @@ public interface MessageRenderer {
                 @NotNull CompilerMessageSeverity severity, @NotNull String message, @NotNull CompilerMessageLocation location
         ) {
             StringBuilder result = new StringBuilder();
-            result.append(severity).append(": ");
+
+            int line = location.getLine();
+            int column = location.getColumn();
+            String lineContent = location.getLineContent();
 
             String path = getPath(location);
             if (path != null) {
                 result.append(path);
-                result.append(": ");
-                if (location.getLine() > 0 && location.getColumn() > 0) {
-                    result.append("(");
-                    result.append(location.getLine()).append(", ").append(location.getColumn());
-                    result.append(") ");
+                result.append(":");
+                if (line > 0) {
+                    result.append(line).append(":");
+                    if (column > 0) {
+                        result.append(column).append(":");
+                    }
                 }
+                result.append(" ");
             }
 
-            result.append(message);
+            result.append(severity.name().toLowerCase());
+            result.append(": ");
+
+            result.append(decapitalizeIfNeeded(message));
+
+            if (lineContent != null && 1 <= column && column <= lineContent.length() + 1) {
+                result.append(LINE_SEPARATOR);
+                result.append(lineContent);
+                result.append(LINE_SEPARATOR);
+                result.append(KotlinPackage.repeat(" ", column - 1));
+                result.append("^");
+            }
 
             return result.toString();
         }
 
+        @NotNull
+        private static String decapitalizeIfNeeded(@NotNull String message) {
+            // TODO: invent something more clever
+            // An ad-hoc heuristic to prevent decapitalization of some names
+            if (message.startsWith("Java") || message.startsWith("Kotlin")) {
+                return message;
+            }
+
+            // For abbreviations and capitalized text
+            if (message.length() >= 2 && Character.isUpperCase(message.charAt(0)) && Character.isUpperCase(message.charAt(1))) {
+                return message;
+            }
+
+            return KotlinPackage.decapitalize(message);
+        }
+
         @Nullable
         protected abstract String getPath(@NotNull CompilerMessageLocation location);