Default FormatterFunc.lint now traps errors from the formatter itse…

…lf, and tries to parse a line number from the error message.

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

@@ -173,8 +173,7 @@ public String compute(String unix, File file) {
 					unix = LineEnding.toUnix(formatted);
 				}
 			} catch (Throwable e) {
-				String relativePath = rootDir.relativize(file.toPath()).toString();
-				exceptionPolicy.handleError(e, step, relativePath);
+				// we ignore exceptions in format because we collect them in lint
 			}
 		}
 		return unix;
@@ -192,8 +191,7 @@ public List<Lint> lint(String content, File file) {
 					totalLints.addAll(lints);
 				}
 			} catch (Throwable e) {
-				String relativePath = rootDir.relativize(file.toPath()).toString();
-				exceptionPolicy.handleError(e, step, relativePath);
+				totalLints.add(Lint.createFromThrowable(step, e));
 			}
 		}
 		if (totalLints.isEmpty()) {

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

@@ -34,8 +34,12 @@ default String apply(String unix, File file) throws Exception {
 		return apply(unix);
 	}
 
-	/** Calculates a list of lints against the given content. */
-	default List<Lint> lint(String content, File file) {
+	/**
+	 * 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 {
+		apply(content, file);
 		return Collections.emptyList();
 	}
 

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

@@ -164,4 +164,43 @@ public static void toFile(List<Lint> lints, File file) throws IOException {
 		byte[] content = toString(lints).getBytes(StandardCharsets.UTF_8);
 		Files.write(file.toPath(), content);
 	}
+
+	/** Attempts to parse a line number from the given exception. */
+	static Lint createFromThrowable(FormatterStep step, Throwable e) {
+		Throwable current = e;
+		while (current != null) {
+			String message = current.getMessage();
+			int lineNumber = lineNumberFor(message);
+			if (lineNumber != -1) {
+				return Lint.create(step.getName(), msgFrom(message), lineNumber);
+			}
+			current = current.getCause();
+		}
+		return Lint.create(step.getName(), ThrowingEx.stacktrace(e), 1);
+	}
+
+	private static int lineNumberFor(String message) {
+		if (message == null) {
+			return -1;
+		}
+		int firstColon = message.indexOf(':');
+		if (firstColon == -1) {
+			return -1;
+		}
+		String candidateNum = message.substring(0, firstColon);
+		try {
+			return Integer.parseInt(candidateNum);
+		} catch (NumberFormatException e) {
+			return -1;
+		}
+	}
+
+	private static String msgFrom(String message) {
+		for (int i = 0; i < message.length(); ++i) {
+			if (Character.isLetter(message.charAt(i))) {
+				return message.substring(i);
+			}
+		}
+		return "";
+	}
 }

lib/src/main/java/com/diffplug/spotless/ThrowingEx.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.
@@ -15,6 +15,9 @@
  */
 package com.diffplug.spotless;
 
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
 /**
  * Basic functional interfaces which throw exception, along with
  * static helper methods for calling them.
@@ -142,4 +145,12 @@ public WrappedAsRuntimeException(Throwable e) {
 			super(e);
 		}
 	}
+
+	public static String stacktrace(Throwable e) {
+		StringWriter out = new StringWriter();
+		PrintWriter writer = new PrintWriter(out);
+		e.printStackTrace(writer);
+		writer.flush();
+		return out.toString();
+	}
 }