Revert "[dart2js] Migrate dart2js_tools to null safety"

This reverts commit 4b1de45.

Reason for revert: Null safety error appears when test fail:
error: Null check operator used on a null value

Original change's description:
> [dart2js] Migrate dart2js_tools to null safety
>
> Change-Id: If93f66f4da2dafb50f58434eb112b1f8af6648c7
> Issue: #46617
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/208363
> Commit-Queue: Nicholas Shahan <nshahan@google.com>
> Reviewed-by: Stephen Adams <sra@google.com>

# Not skipping CQ checks because original CL landed > 1 day ago.

Issue: #46617
Change-Id: I7ef7d95a6715d667698e0dfcb38375fd79b4cc73
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/210540
Reviewed-by: Stephen Adams <sra@google.com>
Commit-Queue: Nicholas Shahan <nshahan@google.com>

.dart_tool/package_config.json

@@ -220,7 +220,7 @@
       "name": "dart2js_tools",
       "rootUri": "../pkg/dart2js_tools",
       "packageUri": "lib/",
-      "languageVersion": "2.12"
+      "languageVersion": "2.3"
     },
     {
       "name": "dart2native",
@@ -812,4 +812,4 @@
       "languageVersion": "2.12"
     }
   ]
-}
+}

pkg/dart2js_tools/bin/deobfuscate.dart

@@ -47,24 +47,24 @@ main(List<String> args) {
   var sb = new StringBuffer();
   try {
     String obfuscatedTrace = new File(args[0]).readAsStringSync();
-    String? error = extractErrorMessage(obfuscatedTrace);
+    String error = extractErrorMessage(obfuscatedTrace);
     var provider = new CachingFileProvider(logger: Logger());
     StackDeobfuscationResult result =
         deobfuscateStack(obfuscatedTrace, provider);
     Frame firstFrame = result.original.frames.first;
-    String? translatedError =
+    String translatedError =
         translate(error, provider.mappingFor(firstFrame.uri));
     if (translatedError == null) translatedError = '<no error message found>';
     printPadded(translatedError, error, sb);
     int longest =
-        result.deobfuscated.frames.fold(0, (m, f) => max(f.member!.length, m));
+        result.deobfuscated.frames.fold(0, (m, f) => max(f.member.length, m));
     for (var originalFrame in result.original.frames) {
       var deobfuscatedFrames = result.frameMap[originalFrame];
       if (deobfuscatedFrames == null) {
         printPadded('no mapping', '${originalFrame.location}', sb);
       } else {
         for (var frame in deobfuscatedFrames) {
-          printPadded('${frame.member!.padRight(longest)} ${frame.location}',
+          printPadded('${frame.member.padRight(longest)} ${frame.location}',
               '${originalFrame.location}', sb);
         }
       }
@@ -77,7 +77,7 @@ main(List<String> args) {
 final green = stdout.hasTerminal ? '\x1b[32m' : '';
 final none = stdout.hasTerminal ? '\x1b[0m' : '';
 
-printPadded(String mapping, String? original, sb) {
+printPadded(String mapping, String original, sb) {
   var len = mapping.length;
   var s = mapping.indexOf('\n');
   if (s >= 0) len -= s + 1;

pkg/dart2js_tools/bin/lookup_name.dart

@@ -2,7 +2,6 @@ import 'dart:io';
 import 'dart:convert';
 import 'package:source_maps/source_maps.dart';
 import 'package:dart2js_tools/src/dart2js_mapping.dart';
-import 'package:dart2js_tools/src/util.dart';
 
 main(List<String> args) {
   if (args.length < 2) {
@@ -17,7 +16,7 @@ main(List<String> args) {
     exit(1);
   }
   var json = jsonDecode(sourcemapFile.readAsStringSync());
-  Dart2jsMapping mapping = Dart2jsMapping(parseSingleMapping(json), json);
+  Dart2jsMapping mapping = Dart2jsMapping(parseJson(json), json);
   var global = mapping.globalNames[name];
   if (global != null) print('$name => $global (a global name)');
   var instance = mapping.instanceNames[name];

pkg/dart2js_tools/bin/show_inline_data.dart

@@ -26,7 +26,7 @@ main(List<String> args) {
   var offsets = frames.keys.toList()..sort();
   var sb = new StringBuffer();
   int depth = 0;
-  int? lastFunctionStart = null;
+  int lastFunctionStart = null;
   for (var offset in offsets) {
     int functionStart = nextFunctionStart(starts, offset, lastFunctionStart);
     if (lastFunctionStart == null || functionStart > lastFunctionStart) {
@@ -43,7 +43,7 @@ main(List<String> args) {
     var pad = ' ' * offsetPrefix.length;
     sb.write(offsetPrefix);
     bool first = true;
-    for (var frame in frames[offset]!) {
+    for (var frame in frames[offset]) {
       if (!first) sb.write('$pad');
       sb.write(' $frame\n');
       first = false;
@@ -75,7 +75,7 @@ List<int> functionStarts(String sources) {
   return result;
 }
 
-int nextFunctionStart(List<int> starts, int offset, int? last) {
+int nextFunctionStart(List<int> starts, int offset, int last) {
   int j = last ?? 0;
   for (; j < starts.length && starts[j] <= offset; j++);
   return j - 1;

pkg/dart2js_tools/lib/deobfuscate_stack_trace.dart

@@ -27,7 +27,7 @@ import 'package:dart2js_tools/src/trace_decoder.dart';
 ///  `//# sourceMappingURL=` line at the end, and load the corresponding
 /// source-map file.
 String deobfuscateStackTrace(String obfuscatedTrace) {
-  String? error = extractErrorMessage(obfuscatedTrace);
+  String error = extractErrorMessage(obfuscatedTrace);
   var provider = CachingFileProvider();
   StackDeobfuscationResult result = deobfuscateStack(obfuscatedTrace, provider);
   Frame firstFrame = result.original.frames.first;
@@ -38,13 +38,13 @@ String deobfuscateStackTrace(String obfuscatedTrace) {
 
   var sb = StringBuffer();
   sb.writeln(translatedError);
-  maxMemberLengthHelper(int m, Frame f) => max(f.member!.length, m);
+  maxMemberLengthHelper(int m, Frame f) => max(f.member.length, m);
   int longest = result.deobfuscated.frames.fold(0, maxMemberLengthHelper);
   longest = result.original.frames.fold(longest, maxMemberLengthHelper);
   for (var originalFrame in result.original.frames) {
     var deobfuscatedFrames = result.frameMap[originalFrame];
     if (deobfuscatedFrames == null) {
-      var name = originalFrame.member!;
+      var name = originalFrame.member;
       sb.writeln('    at ${name.padRight(longest)} ${originalFrame.location}');
     } else {
       for (var frame in deobfuscatedFrames) {
@@ -53,7 +53,7 @@ String deobfuscateStackTrace(String obfuscatedTrace) {
         // client, we can start encoding the function name and remove this
         // workaround.
         if (name == '<unknown>') name = originalFrame.member;
-        sb.writeln('    at ${name!.padRight(longest)} ${frame.location}');
+        sb.writeln('    at ${name.padRight(longest)} ${frame.location}');
       }
     }
   }

pkg/dart2js_tools/lib/src/dart2js_mapping.dart

@@ -23,9 +23,15 @@ class Dart2jsMapping {
   final Map<String, String> globalNames = {};
   final Map<String, String> instanceNames = {};
   final Map<int, List<FrameEntry>> frames = {};
-  late final List<int>? frameIndex = frames.keys.toList()..sort();
+  List<int> _frameIndex;
+  List<int> get frameIndex {
+    if (_frameIndex == null) {
+      _frameIndex = frames.keys.toList()..sort();
+    }
+    return _frameIndex;
+  }
 
-  Dart2jsMapping(this.sourceMap, Map json, {Logger? logger}) {
+  Dart2jsMapping(this.sourceMap, Map json, {Logger logger}) {
     var extensions = json['x_org_dartlang_dart2js'];
     if (extensions == null) return;
     var minifiedNames = extensions['minified_names'];
@@ -35,20 +41,20 @@ class Dart2jsMapping {
       _extractMinifedNames(
           minifiedNames['instance'], sourceMap, instanceNames, logger);
     }
-    String? jsonFrames = extensions['frames'];
+    String jsonFrames = extensions['frames'];
     if (jsonFrames != null) {
       new _FrameDecoder(jsonFrames).parseFrames(frames, sourceMap);
     }
   }
 
-  Dart2jsMapping.json(Map json) : this(parseSingleMapping(json), json);
+  Dart2jsMapping.json(Map json) : this(parseJson(json), json);
 }
 
 class FrameEntry {
-  final String? callUri;
-  final int? callLine;
-  final int? callColumn;
-  final String? inlinedMethodName;
+  final String callUri;
+  final int callLine;
+  final int callColumn;
+  final String inlinedMethodName;
   final bool isEmpty;
   FrameEntry.push(
       this.callUri, this.callLine, this.callColumn, this.inlinedMethodName)
@@ -70,7 +76,7 @@ class FrameEntry {
 }
 
 const _marker = "\n//# sourceMappingURL=";
-Dart2jsMapping? parseMappingFor(Uri uri, {Logger? logger}) {
+Dart2jsMapping parseMappingFor(Uri uri, {Logger logger}) {
   var file = new File.fromUri(uri);
   if (!file.existsSync()) {
     logger?.log('Error: no such file: $uri');
@@ -94,7 +100,7 @@ Dart2jsMapping? parseMappingFor(Uri uri, {Logger? logger}) {
     return null;
   }
   var json = jsonDecode(sourcemapFile.readAsStringSync());
-  return new Dart2jsMapping(parseSingleMapping(json), json, logger: logger);
+  return new Dart2jsMapping(parseJson(json), json, logger: logger);
 }
 
 class _FrameDecoder implements Iterator<String> {
@@ -106,9 +112,8 @@ class _FrameDecoder implements Iterator<String> {
   // Iterator API is used by decodeVlq to consume VLQ entries.
   bool moveNext() => ++index < _length;
 
-  String get current => (index >= 0 && index < _length)
-      ? _internal[index]
-      : throw StateError('No current value available.');
+  String get current =>
+      (index >= 0 && index < _length) ? _internal[index] : null;
 
   bool get hasTokens => index < _length - 1 && _length > 0;
 
@@ -146,15 +151,15 @@ class _FrameDecoder implements Iterator<String> {
 }
 
 _extractMinifedNames(String encodedInput, SingleMapping sourceMap,
-    Map<String, String> minifiedNames, Logger? logger) {
+    Map<String, String> minifiedNames, Logger logger) {
   if (encodedInput.isEmpty) return;
   List<String> input = encodedInput.split(',');
   if (input.length % 2 != 0) {
     logger?.log("Error: expected an even number of entries");
   }
   for (int i = 0; i < input.length; i += 2) {
     String minifiedName = input[i];
-    int id = int.tryParse(input[i + 1])!;
+    int id = int.tryParse(input[i + 1]);
     minifiedNames[minifiedName] = sourceMap.names[id];
   }
 }

pkg/dart2js_tools/lib/src/name_decoder.dart

@@ -9,8 +9,8 @@ import 'package:source_maps/source_maps.dart';
 import 'dart2js_mapping.dart';
 import 'trace.dart';
 
-String? translate(String? error, Dart2jsMapping mapping,
-    [StackTraceLine? line, TargetEntry? entry]) {
+String translate(String error, Dart2jsMapping mapping,
+    [StackTraceLine line, TargetEntry entry]) {
   for (var decoder in _errorMapDecoders) {
     var result = decoder.decode(error, mapping, line, entry);
     // More than one decoder might be applied on a single error message. This
@@ -30,10 +30,10 @@ abstract class ErrorMapDecoder {
   /// Decode [error] that was reported in [line] and has a corresponding [entry]
   /// in the source-map file. The provided [mapping] includes additional
   /// minification data that may be used to decode the error message.
-  String? decode(String? error, Dart2jsMapping mapping, StackTraceLine? line,
-      TargetEntry? entry) {
+  String decode(String error, Dart2jsMapping mapping, StackTraceLine line,
+      TargetEntry entry) {
     if (error == null) return null;
-    Match? lastMatch = null;
+    Match lastMatch = null;
     var result = new StringBuffer();
     for (var match in _matcher.allMatches(error)) {
       var decodedMatch = _decodeInternal(match, mapping, line, entry);
@@ -49,8 +49,8 @@ abstract class ErrorMapDecoder {
     return '$result';
   }
 
-  String? _decodeInternal(Match match, Dart2jsMapping mapping,
-      StackTraceLine? line, TargetEntry? entry);
+  String _decodeInternal(Match match, Dart2jsMapping mapping,
+      StackTraceLine line, TargetEntry entry);
 }
 
 typedef String ErrorDecoder(Match match, Dart2jsMapping mapping,
@@ -59,28 +59,28 @@ typedef String ErrorDecoder(Match match, Dart2jsMapping mapping,
 class MinifiedNameDecoder extends ErrorMapDecoder {
   final RegExp _matcher = new RegExp("minified:([a-zA-Z0-9_\$]*)");
 
-  String? _decodeInternal(Match match, Dart2jsMapping mapping,
-      StackTraceLine? line, TargetEntry? entry) {
+  String _decodeInternal(Match match, Dart2jsMapping mapping,
+      StackTraceLine line, TargetEntry entry) {
     var minifiedName = match.group(1);
-    return mapping.globalNames[minifiedName!];
+    return mapping.globalNames[minifiedName];
   }
 }
 
 class CannotReadPropertyDecoder extends ErrorMapDecoder {
   final RegExp _matcher = new RegExp("Cannot read property '([^']*)' of");
 
-  String? _decodeInternal(Match match, Dart2jsMapping mapping,
-      StackTraceLine? line, TargetEntry? entry) {
+  String _decodeInternal(Match match, Dart2jsMapping mapping,
+      StackTraceLine line, TargetEntry entry) {
     var minifiedName = match.group(1);
-    var name = mapping.instanceNames[minifiedName!];
+    var name = mapping.instanceNames[minifiedName];
     if (name == null) return null;
     return "Cannot read property '$name' of";
   }
 }
 
 abstract class NoSuchMethodDecoderBase extends ErrorMapDecoder {
-  String? _translateMinifiedName(Dart2jsMapping mapping, String? minifiedName) {
-    var name = mapping.instanceNames[minifiedName!];
+  String _translateMinifiedName(Dart2jsMapping mapping, String minifiedName) {
+    var name = mapping.instanceNames[minifiedName];
     if (name != null) return "'$name'";
     if (minifiedName.startsWith(new RegExp(r'(call)?\$[0-9]'))) {
       int first$ = minifiedName.indexOf(r'$');
@@ -89,15 +89,15 @@ abstract class NoSuchMethodDecoderBase extends ErrorMapDecoder {
     return null;
   }
 
-  String? _expandCallSignature(String callSignature) {
+  String _expandCallSignature(String callSignature) {
     // Minified names are one of these forms:
     //   $0         // positional arguments only
     //   $1$2       // type parameters and positional arguments
     //   $3$name    // positional and named arguments
     //   $1$3$name  // type parameters and positional and named args
     var signature = callSignature.split(r'$');
-    int? typeArgs = null;
-    int? totalArgs = null;
+    var typeArgs = null;
+    var totalArgs = null;
     var namedArgs = <String>[];
     for (var arg in signature) {
       if (arg == "") continue;
@@ -115,7 +115,6 @@ abstract class NoSuchMethodDecoderBase extends ErrorMapDecoder {
         namedArgs.add(arg);
       }
     }
-    if (totalArgs == null) return null;
     var sb = new StringBuffer();
     sb.write("'call'");
     sb.write(" (with ");
@@ -137,8 +136,8 @@ class NoSuchMethodDecoder1 extends NoSuchMethodDecoderBase {
   final RegExp _matcher = new RegExp(
       "NoSuchMethodError: method not found: '([^']*)'( on [^\\(]*)? \\(.*\\)");
 
-  String? _decodeInternal(Match match, Dart2jsMapping mapping,
-      StackTraceLine? line, TargetEntry? entry) {
+  String _decodeInternal(Match match, Dart2jsMapping mapping,
+      StackTraceLine line, TargetEntry entry) {
     var minifiedName = match.group(1);
     var suffix = match.group(2) ?? '';
     var name = _translateMinifiedName(mapping, minifiedName);
@@ -151,8 +150,8 @@ class NoSuchMethodDecoder2 extends NoSuchMethodDecoderBase {
   final RegExp _matcher =
       new RegExp("NoSuchMethodError: method not found: '([^']*)'");
 
-  String? _decodeInternal(Match match, Dart2jsMapping mapping,
-      StackTraceLine? line, TargetEntry? entry) {
+  String _decodeInternal(Match match, Dart2jsMapping mapping,
+      StackTraceLine line, TargetEntry entry) {
     var minifiedName = match.group(1);
     var name = _translateMinifiedName(mapping, minifiedName);
     if (name == null) return null;
@@ -163,10 +162,10 @@ class NoSuchMethodDecoder2 extends NoSuchMethodDecoderBase {
 class UnhandledNotAFunctionError extends ErrorMapDecoder {
   final RegExp _matcher = new RegExp("Error: ([^']*) is not a function");
 
-  String? _decodeInternal(Match match, Dart2jsMapping mapping,
-      StackTraceLine? line, TargetEntry? entry) {
+  String _decodeInternal(Match match, Dart2jsMapping mapping,
+      StackTraceLine line, TargetEntry entry) {
     var minifiedName = match.group(1);
-    var name = mapping.instanceNames[minifiedName!];
+    var name = mapping.instanceNames[minifiedName];
     if (name == null) return null;
     return "Error: $name is not a function";
   }

pkg/dart2js_tools/lib/src/sourcemap_helper.dart

@@ -10,7 +10,7 @@ import 'util.dart' show FileProvider;
 
 /// Search backwards in [sources] for a function declaration that includes the
 /// [start] offset.
-TargetEntry? findEnclosingFunction(FileProvider provider, Uri uri, int start) {
+TargetEntry findEnclosingFunction(FileProvider provider, Uri uri, int start) {
   String sources = provider.sourcesFor(uri);
   if (sources == null) return null;
   SourceFile file = provider.fileFor(uri);
@@ -22,7 +22,7 @@ TargetEntry? findEnclosingFunction(FileProvider provider, Uri uri, int start) {
     var line = file.getLine(index);
     var lineEntry = findLine(mapping, line);
     var column = file.getColumn(index);
-    TargetEntry? result = findColumn(line, column, lineEntry);
+    TargetEntry result = findColumn(line, column, lineEntry);
     // If the name entry doesn't start exactly at the column corresponding to
     // `index`, we must be in the middle of a string or code that uses the word
     // "function", but that doesn't have a corresponding mapping. In those
@@ -61,7 +61,7 @@ int nextDeclarationCandidate(String sources, int start) {
 /// number is lower or equal to [line].
 ///
 /// Copied from [SingleMapping._findLine].
-TargetLineEntry? findLine(SingleMapping sourceMap, int line) {
+TargetLineEntry findLine(SingleMapping sourceMap, int line) {
   int index = binarySearch(sourceMap.lines, (e) => e.line > line);
   return (index <= 0) ? null : sourceMap.lines[index - 1];
 }
@@ -73,7 +73,7 @@ TargetLineEntry? findLine(SingleMapping sourceMap, int line) {
 /// the very last entry on that line.
 ///
 /// Copied from [SingleMapping._findColumn].
-TargetEntry? findColumn(int line, int column, TargetLineEntry? lineEntry) {
+TargetEntry findColumn(int line, int column, TargetLineEntry lineEntry) {
   if (lineEntry == null || lineEntry.entries.length == 0) return null;
   if (lineEntry.line != line) return lineEntry.entries.last;
   var entries = lineEntry.entries;