Add a lint method to the core interfaces: Formatter[Step|Func]

Author: nedtwigg

lib/src/main/java/com/diffplug/spotless/FormatterFunc.java

@@ -16,6 +16,7 @@
 package com.diffplug.spotless;
 
 import java.io.File;
+import java.util.List;
 import java.util.Objects;
 
 /**
@@ -32,6 +33,14 @@ default String apply(String unix, File file) throws Exception {
 		return apply(unix);
 	}
 
+	/**
+	 * Calculates a list of lints against the given content.
+	 * By default, that's just an throwables thrown by the lint.
+	 */
+	default List<Lint> lint(String content, File file) throws Exception {
+		return List.of();
+	}
+
 	/**
 	 * {@code Function<String, String>} and {@code BiFunction<String, File, String>} whose implementation
 	 * requires a resource which should be released when the function is no longer needed.
@@ -74,6 +83,14 @@ public String apply(String unix) throws Exception {
 		@FunctionalInterface
 		interface ResourceFunc<T extends AutoCloseable> {
 			String apply(T resource, String unix) throws Exception;
+
+			/**
+			 * Calculates a list of lints against the given content.
+			 * By default, that's just an throwables thrown by the lint.
+			 */
+			default List<Lint> lint(T resource, String unix) throws Exception {
+				return List.of();
+			}
 		}
 
 		/** Creates a {@link FormatterFunc.Closeable} which uses the given resource to execute the format function. */
@@ -101,6 +118,10 @@ public String apply(String unix) throws Exception {
 		@FunctionalInterface
 		interface ResourceFuncNeedsFile<T extends AutoCloseable> {
 			String apply(T resource, String unix, File file) throws Exception;
+
+			default List<Lint> lint(T resource, String content, File file) throws Exception {
+				return List.of();
+			}
 		}
 
 		/** Creates a {@link FormatterFunc.Closeable} which uses the given resource to execute the file-dependent format function. */
@@ -123,6 +144,11 @@ public String apply(String unix, File file) throws Exception {
 				public String apply(String unix) throws Exception {
 					return apply(unix, Formatter.NO_FILE_SENTINEL);
 				}
+
+				@Override
+				public List<Lint> lint(String content, File file) throws Exception {
+					return function.lint(resource, content, file);
+				}
 			};
 		}
 	}

lib/src/main/java/com/diffplug/spotless/FormatterStep.java

@@ -17,6 +17,7 @@
 
 import java.io.File;
 import java.io.Serializable;
+import java.util.List;
 import java.util.Objects;
 
 import javax.annotation.Nullable;
@@ -46,6 +47,22 @@ public interface FormatterStep extends Serializable, AutoCloseable {
 	@Nullable
 	String format(String rawUnix, File file) throws Exception;
 
+	/**
+	 * Returns a list of lints against the given file content
+	 *
+	 * @param content
+	 *            the content to check
+	 * @param file
+	 *            the file which {@code content} was obtained from; never null. Pass an empty file using
+	 *            {@code new File("")} if and only if no file is actually associated with {@code content}
+	 * @return a list of lints
+	 * @throws Exception if the formatter step experiences a problem
+	 */
+	@Nullable
+	default List<Lint> lint(String content, File file) throws Exception {
+		return List.of();
+	}
+
 	/**
 	 * Returns a new {@code FormatterStep} which, observing the value of {@code formatIfMatches},
 	 * will only apply, or not, its changes to files which pass the given filter.