Improved fingerprint handling for Checkstyle

Author: chkal

src/main/java/de/chkal/maven/gitlab/codequality/checkstyle/CheckstyleFindingProvider.java

@@ -65,13 +65,10 @@ private Finding transformErrorType(FileType fileType, ErrorType errorType) {
 
     Finding finding = new Finding();
     finding.setDescription(String.format("%s: %s", getName(), errorType.getMessage()));
+    finding.setFingerprint(createFingerprint(fileType, errorType));
     finding.setSeverity(getSeverity(errorType.getSeverity()));
     finding.setPath(getRepositoryRelativePath(fileType));
     finding.setLine(getLineNumber(errorType));
-
-    // Checkstyle doesn't provide any fingerprints, so we create our own one
-    autoGenerateFingerprint(finding);
-
     return finding;
 
   }
@@ -94,18 +91,32 @@ private Severity getSeverity(String severity) {
     }
   }
 
-  private void autoGenerateFingerprint(Finding finding) {
+  private String createFingerprint(FileType fileType, ErrorType errorType) {
 
     try {
 
-      String key = String.format("%s:%s:%d",
-          finding.getDescription(), finding.getPath(), finding.getLine());
+      /*
+       * The fingerprint is created from:
+       *   - file path
+       *   - severity
+       *   - message text
+       *   - column index (which will most likely not change for a finding)
+       *
+       * We do NOT use:
+       *   - line number (will change if code is added/removed above or below the finding)
+       */
+      String key = String.format("%s:%s:%s:%s",
+          getRepositoryRelativePath(fileType),
+          errorType.getSeverity(),
+          errorType.getMessage(),
+          errorType.getColumn()
+      );
 
       MessageDigest sha1Digest = MessageDigest.getInstance("SHA256");
       sha1Digest.update(key.getBytes(StandardCharsets.UTF_8));
       byte[] digest = sha1Digest.digest();
 
-      finding.setFingerprint(DatatypeConverter.printHexBinary(digest).toLowerCase(Locale.ROOT));
+      return DatatypeConverter.printHexBinary(digest).toLowerCase(Locale.ROOT);
 
     } catch (NoSuchAlgorithmException e) {
       throw new RuntimeException(e);

src/test/java/de/chkal/maven/gitlab/codequality/checkstyle/CheckstyleFindingProviderTest.java

@@ -25,14 +25,16 @@ void shouldParseCheckstyleFileWithoutNamespace() throws IOException {
 
       Finding first = findings.get(0);
       assertThat(first.getDescription()).startsWith("Checkstyle: 'static' modifier out of order");
-      assertThat(first.getFingerprint()).isNotBlank();
+      assertThat(first.getFingerprint())
+          .isEqualTo("ab6037e7ca18412687356d3460d9eb6e73777d004168730864daaabe993df2bc");
       assertThat(first.getSeverity()).isEqualTo(Severity.MAJOR);
       assertThat(first.getPath()).isEqualTo("src/main/java/com/example/myapp/Bar.java");
       assertThat(first.getLine()).isEqualTo(25);
 
       Finding second = findings.get(1);
       assertThat(second.getDescription()).startsWith("Checkstyle: 'if' child has incorrect");
-      assertThat(second.getFingerprint()).isNotBlank();
+      assertThat(second.getFingerprint())
+          .isEqualTo("cf3472bc41cca24f7a5bfc1278cc873effc31053f729c4c0c111aa95bdb5a267");
       assertThat(second.getSeverity()).isEqualTo(Severity.MAJOR);
       assertThat(second.getPath()).isEqualTo("src/main/java/com/example/myapp/Bar.java");
       assertThat(second.getLine()).isEqualTo(90);