fix(baseline): key every fingerprint on identity, not on its line

A finding with no discriminating key fell back to `line=N`, and three rules
had none: a dormant emitted-not-rendered union carried only {union, owner},
and notifier-field-unread and notifier-inert-consumer only {owner}.
loading-not-reset embedded the catch's absolute line as `catchLine`. Any edit
above one of those findings changed its fingerprint, so `check --baseline`
re-reported an accepted finding as new and `verify` reported its entry as
RESOLVED.

union and owner now count as discriminating (each of those rules emits at most
one finding per union or notifier), and loading-not-reset carries `catchSite`,
the catch's index among the catch clauses of its enclosing member
(`twoSwallowedAwaits#1`), which does not move when code outside the member
does.

The test that guarded this shifted only findings.first. It now shifts every
finding, and a second test really inserts lines at the top of every fixture
file, re-analyses, and requires the same fingerprint set.

Migration: fingerprints change for emitted-not-rendered (dormant unions),
notifier-field-unread, notifier-inert-consumer and loading-not-reset. Old
baselines stay readable and keep working - both `check --baseline` and
`verify` also match the version-1 fingerprint (`legacyFingerprint`) - but
those entries stay line-sensitive until the baseline is rewritten with
--write-baseline, which now writes `"version": 2`.

lib/src/rules.dart

@@ -60,7 +60,69 @@ class Finding {
   final bool baselined;
 
   /// Stable identity that survives line shifts, used to ratchet a baseline.
+  ///
+  /// Every rule now carries a semantic key, so `line=` is a last resort for a
+  /// finding with no identity at all. It used to be the norm for three rules -
+  /// a dormant emitted-not-rendered union and both notifier-level rules carried
+  /// only {union, owner} or {owner}, which did not count as discriminating - and
+  /// loading-not-reset embedded the catch's absolute line. Any edit above such a
+  /// finding changed its identity, so a baseline re-reported it as new and
+  /// `verify` reported the old entry as resolved.
   String get fingerprint {
+    final parts = <String>[rule, file ?? ''];
+    final seen = <String>{};
+    for (final key in const [
+      'union',
+      'variant',
+      'group',
+      'event',
+      'provider',
+      'owner',
+      'member',
+      'stateType',
+      'valueType',
+      'call',
+      'catchSite',
+    ]) {
+      final value = data[key];
+      if (value != null) {
+        parts.add('$key=$value');
+        seen.add(key);
+      }
+    }
+    // Findings with no discriminating key at all would collide, so fall back to
+    // the position.
+    const discriminating = {
+      // A union or owner is one finding per file for the rules that carry only
+      // that: one dormant union, one unread-member list or one inert notifier
+      // per class.
+      'union',
+      'owner',
+      'variant',
+      'group',
+      'event',
+      'provider',
+      'stateType',
+      'valueType',
+      'call',
+      // A member name is semantic identity, not position: adding it keeps
+      // fingerprints stable when code moves.
+      'member',
+      // The one rule that can emit two findings with the same owner and member
+      // (two swallowed catches in one method) carries the catch's index within
+      // its enclosing member, which does not move when code above it does.
+      'catchSite',
+    };
+    if (seen.intersection(discriminating).isEmpty && line != null) {
+      parts.add('line=$line');
+    }
+    return parts.join('|');
+  }
+
+  /// The identity baselines written before [fingerprint] stopped depending on
+  /// line numbers used. Matching it keeps an older baseline working: its
+  /// entries still suppress and verify, until it is rewritten.
+  String get legacyFingerprint {
     final parts = <String>[rule, file ?? ''];
     final seen = <String>{};
     for (final key in const [
@@ -82,8 +144,6 @@ class Finding {
         seen.add(key);
       }
     }
-    // Findings with no discriminating key (two methods of the same rule in the
-    // same file, say) would collide, so fall back to the position.
     const discriminating = {
       'variant',
       'group',
@@ -92,10 +152,6 @@ class Finding {
       'stateType',
       'valueType',
       'call',
-      // A member name is semantic identity, not position: adding it keeps
-      // fingerprints stable when code moves. The one rule that can emit two
-      // findings with the same owner and member (two swallowed catches in one
-      // method) carries an explicit `catchLine` key instead.
       'member',
       'catchLine',
     };
@@ -105,6 +161,10 @@ class Finding {
     return parts.join('|');
   }
 
+  /// True when [accepted] holds this finding under either identity.
+  bool isAcceptedBy(Set<String> accepted) =>
+      accepted.contains(fingerprint) || accepted.contains(legacyFingerprint);
+
   /// Human-readable identity used in baseline entries and verify output.
   String get baselineLabel {
     final data = this.data;
@@ -776,9 +836,7 @@ FindingReport runChecks({
       ? findings
       : [
           for (final finding in findings)
-            baseline.contains(finding.fingerprint)
-                ? finding.asBaselined()
-                : finding,
+            finding.isAcceptedBy(baseline) ? finding.asBaselined() : finding,
         ];
   resolved.sort((a, b) {
     final bySeverity = _severityRank(
@@ -811,8 +869,10 @@ String encodeBaseline(String root, List<Finding> findings) {
     byFingerprint.putIfAbsent(finding.fingerprint, () => finding);
   }
   final fingerprints = byFingerprint.keys.toList()..sort();
+  // Version 2: fingerprints no longer embed line numbers for rules with a
+  // semantic identity. Version-1 fingerprints are still matched on read.
   return const JsonEncoder.withIndent('  ').convert(<String, Object?>{
-    'version': 1,
+    'version': 2,
     'root': root,
     'fingerprints': fingerprints,
     'entries': [
@@ -1176,6 +1236,16 @@ class _BodyScan extends RecursiveAstVisitor<void> {
   void visitFunctionDeclaration(FunctionDeclaration node) {}
 }
 
+class _CatchCollector extends RecursiveAstVisitor<void> {
+  final List<CatchClause> clauses = [];
+
+  @override
+  void visitCatchClause(CatchClause node) {
+    clauses.add(node);
+    super.visitCatchClause(node);
+  }
+}
+
 class _HasAwait extends RecursiveAstVisitor<void> {
   bool found = false;
 
@@ -1202,6 +1272,10 @@ class _LoadingResetCollector extends RecursiveAstVisitor<void> {
   final List<Finding> findings;
   final List<String> _classStack = [];
 
+  /// Enclosing named members (method, function, constructor), innermost last,
+  /// so a catch in a closure is placed relative to the member that holds it.
+  final List<({String name, AstNode node})> _members = [];
+
   static final RegExp _stateAssign = RegExp(r'(^|[^.\w])state\s*=(?!=)');
   static final RegExp _throwing = RegExp(r'\b(rethrow|throw)\b');
   static final RegExp _errorish = RegExp(
@@ -1225,8 +1299,28 @@ class _LoadingResetCollector extends RecursiveAstVisitor<void> {
 
   @override
   void visitMethodDeclaration(MethodDeclaration node) {
+    _members.add((name: node.name.lexeme, node: node));
     _analyze(node.body, node.name.lexeme);
     super.visitMethodDeclaration(node);
+    _members.removeLast();
+  }
+
+  @override
+  void visitFunctionDeclaration(FunctionDeclaration node) {
+    _members.add((name: node.name.lexeme, node: node));
+    super.visitFunctionDeclaration(node);
+    _members.removeLast();
+  }
+
+  @override
+  void visitConstructorDeclaration(ConstructorDeclaration node) {
+    final name = node.name;
+    _members.add((
+      name: name == null ? 'new' : 'new ${name.lexeme}',
+      node: node,
+    ));
+    super.visitConstructorDeclaration(node);
+    _members.removeLast();
   }
 
   @override
@@ -1235,6 +1329,19 @@ class _LoadingResetCollector extends RecursiveAstVisitor<void> {
     super.visitFunctionExpression(node);
   }
 
+  /// `member#index`: the catch's position among every catch clause of its
+  /// enclosing member, in source order. Unlike its line, this does not change
+  /// when code outside that member moves.
+  String _catchSite(CatchClause clause, FunctionBody body) {
+    final enclosing = _members.isEmpty ? null : _members.last;
+    final collector = _CatchCollector();
+    (enclosing?.node ?? body).accept(collector);
+    final index = collector.clauses.indexWhere(
+      (candidate) => identical(candidate, clause),
+    );
+    return '${enclosing?.name ?? '<closure>'}#$index';
+  }
+
   void _analyze(FunctionBody? body, String member) {
     if (body == null) return;
     final owner = _classStack.isEmpty ? '<top>' : _classStack.last;
@@ -1282,8 +1389,11 @@ class _LoadingResetCollector extends RecursiveAstVisitor<void> {
             data: {
               'owner': owner,
               'member': member,
-              // A method can hold more than one swallowed catch, so position is
-              // part of this rule's identity.
+              // A method can hold more than one swallowed catch, so the catch's
+              // place in its member is part of this rule's identity.
+              'catchSite': _catchSite(catchClause, body),
+              // Kept for reading version-1 baselines, whose fingerprints
+              // embedded it; no longer part of the fingerprint.
               'catchLine': lineInfo.getLocation(catchClause.offset).lineNumber,
             },
           ),

lib/src/verify.dart

@@ -170,7 +170,15 @@ VerificationReport verifyAgainstBaseline({
     for (final entry in baseline)
       if (rules == null || rules.contains(baselineEntryRule(entry))) entry,
   ];
-  final present = {for (final finding in report.findings) finding.fingerprint};
+  // A finding is present under its current identity or the one a version-1
+  // baseline recorded, so an older baseline does not read every changed
+  // fingerprint as a fix.
+  final present = {
+    for (final finding in report.findings) ...[
+      finding.fingerprint,
+      finding.legacyFingerprint,
+    ],
+  };
   final accepted = {for (final entry in baseline) entry.fingerprint};
   final notScanned = <BaselineEntry>[];
   final resolved = <BaselineEntry>[];
@@ -192,7 +200,7 @@ VerificationReport verifyAgainstBaseline({
     notScanned: notScanned,
     newFindings: [
       for (final finding in report.findings)
-        if (!accepted.contains(finding.fingerprint)) finding,
+        if (!finding.isAcceptedBy(accepted)) finding,
     ],
   );
 }

test/baseline_test.dart

@@ -1,3 +1,5 @@
+import 'dart:io';
+
 import 'package:pipe/pipe.dart';
 import 'package:test/test.dart';
 
@@ -33,7 +35,7 @@ void main() {
       hasLength(analysis.report.findings.length),
       reason: 'fingerprints should be unique per finding',
     );
-    expect(encoded, contains('"version": 1'));
+    expect(encoded, contains('"version": 2'));
   });
 
   test('a baseline turns every existing finding into an accepted one', () {
@@ -65,21 +67,95 @@ void main() {
     expect(fresh.newFindings, hasLength(analysis.report.findings.length));
   });
 
-  test('fingerprints are stable across rule identity, not line numbers', () {
-    final finding = analysis.report.findings.first;
-    // Moving the finding down the file must not change its identity.
-    final moved = Finding(
-      rule: finding.rule,
-      severity: finding.severity,
-      confidence: finding.confidence,
-      message: finding.message,
-      file: finding.file,
-      line: (finding.line ?? 1) + 500,
-      evidence: finding.evidence,
-      remediation: finding.remediation,
-      data: finding.data,
+  test('no fingerprint depends on the line its finding sits on', () {
+    // Shifting only findings.first proved nothing about the other rules: three
+    // of them fell back to `line=` and loading-not-reset embedded the catch's
+    // absolute line, so moving code broke their baseline entries.
+    expect(analysis.report.findings, isNotEmpty);
+    for (final finding in analysis.report.findings) {
+      final catchLine = finding.data['catchLine'];
+      final moved = Finding(
+        rule: finding.rule,
+        severity: finding.severity,
+        confidence: finding.confidence,
+        message: finding.message,
+        file: finding.file,
+        line: (finding.line ?? 1) + 500,
+        evidence: finding.evidence,
+        remediation: finding.remediation,
+        // Line-valued data moves with the code.
+        data: {
+          ...finding.data,
+          if (catchLine is int) 'catchLine': catchLine + 500,
+        },
+      );
+      expect(
+        moved.fingerprint,
+        finding.fingerprint,
+        reason: '${finding.rule} at ${finding.location}',
+      );
+    }
+  });
+
+  test('inserting lines above every finding keeps every identity', () async {
+    // The end-to-end version of the test above: really move the code, re-run
+    // the analysis, and compare. Positional data derived from the AST (such as
+    // a catch's place in its method) is exercised here, not simulated.
+    final temp = Directory.systemTemp.createTempSync('pipe-shifted');
+    _copyTree(Directory(fixturePath), temp);
+    for (final entity in Directory('${temp.path}/lib').listSync()) {
+      if (entity is! File || !entity.path.endsWith('.dart')) continue;
+      entity.writeAsStringSync(
+        '// shifted\n' * 7 + entity.readAsStringSync(),
+      );
+    }
+    final shifted = await analyzeProject(
+      await loadProject(temp.path),
+      concurrency: 1,
     );
-    expect(moved.fingerprint, finding.fingerprint);
+    try {
+      final lines = {
+        for (final finding in analysis.report.findings)
+          if (finding.line != null) finding.line!,
+      };
+      final shiftedLines = {
+        for (final finding in shifted.report.findings)
+          if (finding.line != null) finding.line!,
+      };
+      expect(shiftedLines, isNot(lines), reason: 'the code must have moved');
+      expect(
+        {for (final finding in shifted.report.findings) finding.fingerprint},
+        {for (final finding in analysis.report.findings) finding.fingerprint},
+      );
+    } finally {
+      await shifted.dispose();
+    }
+  });
+
+  test('a version-1 baseline still accepts the findings it recorded', () {
+    // Fingerprints changed for rules that used to embed a line; an older
+    // baseline must keep suppressing them rather than report them all as new.
+    final legacy = {
+      for (final finding in analysis.report.findings) finding.legacyFingerprint,
+    };
+    final baselined = reportWith(legacy);
+    expect(baselined.newFindings, isEmpty);
+
+    final entries = [
+      for (final fingerprint in legacy)
+        BaselineEntry(
+          fingerprint: fingerprint,
+          rule: fingerprint.split('|').first,
+          file: fingerprint.split('|')[1],
+          label: fingerprint,
+        ),
+    ];
+    final verification = verifyAgainstBaseline(
+      report: analysis.report,
+      baseline: entries,
+    );
+    expect(verification.resolved, isEmpty);
+    expect(verification.newFindings, isEmpty);
   });
 
   test('a member name is a semantic key, so moving that code keeps identity', () {
@@ -105,9 +181,9 @@ void main() {
   });
 
   test('two findings in one method still get distinct fingerprints', () {
-    // A method can hold more than one swallowed catch, so this rule carries an
-    // explicit catchLine: it needs position to stay distinguishable while other
-    // rules stay line-independent.
+    // A method can hold more than one swallowed catch, so this rule carries the
+    // catch's index within its member: position enough to tell the two apart,
+    // without the absolute line that broke identity whenever code moved.
     final catches = analysis.report.findings
         .where(
           (f) =>
@@ -131,3 +207,16 @@ void main() {
     );
   });
 }
+
+void _copyTree(Directory from, Directory to) {
+  to.createSync(recursive: true);
+  for (final entity in from.listSync(recursive: true)) {
+    final relative = entity.path.substring(from.path.length + 1);
+    final target = '${to.path}/$relative';
+    if (entity is Directory) {
+      Directory(target).createSync(recursive: true);
+    } else if (entity is File) {
+      File(target).writeAsBytesSync(entity.readAsBytesSync());
+    }
+  }
+}