Fix the sample code analyzer to properly handle `missing_identifier` errors (#87593)

This fixes how the sample analyzer handles missing_identifier errors. It was looking at the wrong line, and missing an else clause, so it was silently allowing missing_identifier errors to pass.

In addition, this fixes the sample generation so that it uses the correct filename for the output files: it previously was looking for the first line that had a filename, which was meant to indicate a non-generated line. This change adds a new Line.generated constructor for generated lines, so that they can also have the correct filename associated with them.

dev/bots/analyze.dart

@@ -109,7 +109,7 @@ Future<void> run(List<String> arguments) async {
   // Analyze all the sample code in the repo
   print('$clock Sample code...');
   await runCommand(dart,
-    <String>[path.join(flutterRoot, 'dev', 'bots', 'analyze_sample_code.dart'), '--verbose'],
+    <String>[path.join(flutterRoot, 'dev', 'bots', 'analyze_sample_code.dart')],
     workingDirectory: flutterRoot,
   );
 

dev/bots/test/analyze-sample-code-test-input/known_broken_documentation.dart

@@ -113,6 +113,14 @@
 /// ```
 /// {@end-tool}
 ///
+/// {@tool snippet}
+/// snippet with trailing comma
+///
+/// ```dart
+/// const SizedBox(),
+/// ```
+/// {@end-tool}
+///
 /// {@tool dartpad --template=stateless_widget_material}
 /// Dartpad with null-safe syntax
 ///

dev/bots/test/analyze_sample_code_test.dart

@@ -24,7 +24,7 @@ void main() {
       ..removeWhere((String line) => line.startsWith('Analyzer output:') || line.startsWith('Building flutter tool...'));
     expect(process.exitCode, isNot(equals(0)));
     expect(stderrLines, <String>[
-      'In sample starting at dev/bots/test/analyze-sample-code-test-input/known_broken_documentation.dart:117:      child: Text(title),',
+      'In sample starting at dev/bots/test/analyze-sample-code-test-input/known_broken_documentation.dart:125:      child: Text(title),',
       ">>> error: The final variable 'title' can't be read because it is potentially unassigned at this point (read_potentially_unassigned_final)",
       'dev/bots/test/analyze-sample-code-test-input/known_broken_documentation.dart:30:9: new Opacity(',
       '>>> info: Unnecessary new keyword (unnecessary_new)',
@@ -36,12 +36,14 @@ void main() {
       '>>> info: Prefer const over final for declarations (prefer_const_declarations)',
       'dev/bots/test/analyze-sample-code-test-input/known_broken_documentation.dart:112:25: final int foo = null;',
       ">>> error: A value of type 'Null' can't be assigned to a variable of type 'int' (invalid_assignment)",
+      'dev/bots/test/analyze-sample-code-test-input/known_broken_documentation.dart:120:24: const SizedBox(),',
+      '>>> error: Unexpected comma at end of sample code. (missing_identifier)',
       '',
       'Found 2 sample code errors.',
       ''
     ]);
     expect(stdoutLines, <String>[
-      'Found 8 snippet code blocks, 0 sample code sections, and 2 dartpad sections.',
+      'Found 9 snippet code blocks, 0 sample code sections, and 2 dartpad sections.',
       'Starting analysis of code samples.',
       '',
     ]);
@@ -60,7 +62,7 @@ void main() {
     expect(process.exitCode, isNot(equals(0)));
     expect(stdoutLines, equals(<String>[
       // There is one sample code section in the test's dummy dart:ui code.
-      'Found 8 snippet code blocks, 1 sample code sections, and 2 dartpad sections.',
+      'Found 9 snippet code blocks, 1 sample code sections, and 2 dartpad sections.',
       '',
     ]));
   });

packages/flutter/lib/src/painting/strut_style.dart

@@ -142,7 +142,7 @@ import 'text_style.dart';
 ///     fontSize: 30,
 ///     height: 1.5,
 ///   ),
-/// ),
+/// )
 /// ```
 /// {@end-tool}
 ///
@@ -183,7 +183,7 @@ import 'text_style.dart';
 ///     fontFamily: 'Roboto',
 ///     height: 1.5,
 ///   ),
-/// ),
+/// )
 /// ```
 /// {@end-tool}
 ///
@@ -226,7 +226,7 @@ import 'text_style.dart';
 ///     height: 1,
 ///     forceStrutHeight: true,
 ///   ),
-/// ),
+/// )
 /// ```
 /// {@end-tool}
 ///