Improve error messages.

Author: nedtwigg

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

@@ -90,7 +90,7 @@ public List<Lint> lint(String raw, File file) {
 					var matcher = regex.matcher(raw);
 					while (matcher.find()) {
 						int line = 1 + (int) raw.codePoints().limit(matcher.start()).filter(c -> c == '\n').count();
-						lints.add(Lint.atLine(line, ruleId, lintDetail));
+						lints.add(Lint.atLine(line, matcher.group(0), lintDetail));
 					}
 					return lints;
 				}

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

@@ -31,12 +31,14 @@ void formatter() throws Exception {
 
 	@Test
 	void lint() throws Exception {
-		FormatterStep step = ReplaceRegexStep.lint("regex", "bad", "no bad words");
+		FormatterStep step = ReplaceRegexStep.lint("stayPositive", "(bad|awful)", "no negative words");
 		StepHarness.forStep(step)
 				.expectLintsOf(StringPrinter.buildStringFromLines(
 						"bad",
-						"x bad y",
-						"ok"))
-				.toBe("L1 regex(bad) no bad words\nL2 regex(bad) no bad words");
+						"oh boy",
+						"x awful y",
+						"yippeee"))
+				.toBe("L1 stayPositive(bad) no negative words",
+						"L3 stayPositive(awful) no negative words");
 	}
 }