Update IndentStep to allow leading space on multi-line comments

At present, `indentWithTabs` doesn't handle leading space on multi-line comments and reports errors on properly formatted code.

This commit updates `IndentStep` to add support for detecting multi-line comments and allowing a single leading space for such lines.

Closes #1070

lib/src/main/java/com/diffplug/spotless/generic/IndentStep.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 DiffPlug
+ * Copyright 2016-2022 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -100,6 +100,15 @@ String format(String raw) {
 					++contentStart;
 				}
 
+				// detect multi-line comments
+				boolean multiLineComment = false;
+				if (contentStart < raw.length() && raw.charAt(contentStart) == '*') {
+					multiLineComment = true;
+					if (contentStart == lineStart) {
+						++numSpaces; // multi-line comment without a leading space
+					}
+				}
+
 				// add the leading space in a canonical way
 				if (numSpaces > 0) {
 					switch (state.type) {
@@ -112,6 +121,9 @@ String format(String raw) {
 						for (int i = 0; i < numSpaces / state.numSpacesPerTab; ++i) {
 							builder.append('\t');
 						}
+						if (multiLineComment) {
+							builder.append(' ');
+						}
 						break;
 					default:
 						throw new IllegalArgumentException("Unexpected enum " + state.type);

testlib/src/main/resources/indent/IndentedWithSpace.test

@@ -2,8 +2,13 @@ package com.github.youribonnaffe.gradle.format;
 
 import java.util.function.Function;
 
-
+/**
+ * Test class.
+ */
 public class Java8Test {
+    /**
+     * Test method.
+     */
     public void doStuff() throws Exception {
         Function<String, Integer> example = Integer::parseInt;
         example.andThen(val -> {
@@ -21,7 +26,10 @@ public class Java8Test {
                 throw new Exception();
         }
     }
-
+
+    /**
+     * Test enum.
+     */
     public enum SimpleEnum {
         A, B, C;
     }

testlib/src/main/resources/indent/IndentedWithTab.test

@@ -2,8 +2,13 @@ package com.github.youribonnaffe.gradle.format;
 
 import java.util.function.Function;
 
-
+/**
+ * Test class.
+ */
 public class Java8Test {
+	/**
+	 * Test method.
+	 */
 	public void doStuff() throws Exception {
 		Function<String, Integer> example = Integer::parseInt;
 		example.andThen(val -> {
@@ -21,7 +26,10 @@ public class Java8Test {
 				throw new Exception();
 		}
 	}
-
+
+	/**
+	 * Test enum.
+	 */
 	public enum SimpleEnum {
 		A, B, C;
 	}

testlib/src/test/java/com/diffplug/spotless/generic/IndentStepTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 DiffPlug
+ * Copyright 2016-2022 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -82,4 +82,19 @@ protected FormatterStep create() {
 			}
 		}.testEquals();
 	}
+
+	@Test
+	void allowLeadingSpaceIfMultiLineComment() {
+		FormatterStep indent = IndentStep.Type.TAB.create(4);
+		Assertions.assertAll("class multi-line comments",
+			() -> Assertions.assertEquals(" * test", indent.format("* test", new File(""))),
+			() -> Assertions.assertEquals(" * test", indent.format(" * test", new File(""))),
+			() -> Assertions.assertEquals(" * test", indent.format("  * test", new File(""))),
+			() -> Assertions.assertEquals(" * test", indent.format("   * test", new File(""))));
+		Assertions.assertAll("method multi-line comments",
+			() -> Assertions.assertEquals("\t * test", indent.format("\t* test", new File(""))),
+			() -> Assertions.assertEquals("\t * test", indent.format("\t * test", new File(""))),
+			() -> Assertions.assertEquals("\t * test", indent.format("\t  * test", new File(""))),
+			() -> Assertions.assertEquals("\t * test", indent.format("\t   * test", new File(""))));
+	}
 }