[flutter_tools] Upgrade only from flutter update-packages (#103924)

packages/flutter_tools/lib/src/commands/update_packages.dart

@@ -382,9 +382,9 @@ class UpdatePackagesCommand extends FlutterCommand {
       final File fakePackage = _pubspecFor(tempDir);
       fakePackage.createSync();
       fakePackage.writeAsStringSync(
-        _generateFakePubspec(
+        generateFakePubspec(
           dependencies,
-          useAnyVersion: doUpgrade,
+          doUpgrade: doUpgrade,
         ),
       );
       // Create a synthetic flutter SDK so that transitive flutter SDK
@@ -1321,8 +1321,22 @@ class PubspecDependency extends PubspecLine {
 
   /// This generates the entry for this dependency for the pubspec.yaml for the
   /// fake package that we'll use to get the version numbers figured out.
-  void describeForFakePubspec(StringBuffer dependencies, StringBuffer overrides, { bool useAnyVersion = true}) {
-    final String versionToUse = useAnyVersion || version.isEmpty ? 'any' : version;
+  ///
+  /// When called with [doUpgrade] as [true], the version constrains will be set
+  /// to >= whatever the previous version was. If [doUpgrade] is [false], then
+  /// the previous version is used again as an exact pin.
+  void describeForFakePubspec(StringBuffer dependencies, StringBuffer overrides, { bool doUpgrade = true }) {
+    final String versionToUse;
+    // This should only happen when manually adding new dependencies; otherwise
+    // versions should always be pinned exactly
+    if (version.isEmpty || version == 'any') {
+      versionToUse = 'any';
+    } else if (doUpgrade) {
+      // Must wrap in quotes for Yaml parsing
+      versionToUse = "'>= $version'";
+    } else {
+      versionToUse = version;
+    }
     switch (kind) {
       case DependencyKind.unknown:
       case DependencyKind.overridden:
@@ -1362,6 +1376,7 @@ class PubspecDependency extends PubspecLine {
           dependencies.writeln('  $name:');
           dependencies.writeln(lockLine);
         }
+        break;
     }
   }
 
@@ -1379,13 +1394,14 @@ File _pubspecFor(Directory directory) {
 
 /// Generates the source of a fake pubspec.yaml file given a list of
 /// dependencies.
-String _generateFakePubspec(
+@visibleForTesting
+String generateFakePubspec(
   Iterable<PubspecDependency> dependencies, {
-  bool useAnyVersion = false
+  bool doUpgrade = false
 }) {
   final StringBuffer result = StringBuffer();
   final StringBuffer overrides = StringBuffer();
-  final bool verbose = useAnyVersion;
+  final bool verbose = doUpgrade;
   result.writeln('name: flutter_update_packages');
   result.writeln('environment:');
   result.writeln("  sdk: '>=2.10.0 <3.0.0'");
@@ -1415,7 +1431,7 @@ String _generateFakePubspec(
   }
   for (final PubspecDependency dependency in dependencies) {
     if (!dependency.pointsToSdk) {
-      dependency.describeForFakePubspec(result, overrides, useAnyVersion: useAnyVersion);
+      dependency.describeForFakePubspec(result, overrides, doUpgrade: doUpgrade);
     }
   }
   result.write(overrides.toString());

packages/flutter_tools/test/commands.shard/hermetic/update_packages_test.dart

@@ -12,6 +12,7 @@ import 'package:flutter_tools/src/commands/update_packages.dart';
 import 'package:flutter_tools/src/dart/pub.dart';
 import 'package:meta/meta.dart';
 import 'package:test/fake.dart';
+import 'package:yaml/yaml.dart';
 
 import '../../src/common.dart';
 import '../../src/context.dart';
@@ -173,6 +174,47 @@ void main() {
       ),
     });
   });
+
+  group('generateFakePubspec', () {
+    const String prevVersion = '1.2.0';
+    testUsingContext('constrains package versions to >= previous version if doUpgrade: true', () {
+      final String pubspecSource = generateFakePubspec(
+        <PubspecDependency>[
+          PubspecDependency(
+            '  foo: $prevVersion',
+            'foo',
+            '',
+            version: prevVersion,
+            sourcePath: '/path/to/pubspec.yaml',
+            kind: DependencyKind.normal,
+            isTransitive: false,
+          ),
+        ],
+        doUpgrade: true,
+      );
+      final YamlMap pubspec = loadYaml(pubspecSource) as YamlMap;
+      expect((pubspec['dependencies'] as YamlMap)['foo'], '>= $prevVersion');
+    });
+
+    testUsingContext('uses previous package versions doUpgrade: false', () {
+      final String pubspecSource = generateFakePubspec(
+        <PubspecDependency>[
+          PubspecDependency(
+            '  foo: $prevVersion',
+            'foo',
+            '',
+            version: prevVersion,
+            sourcePath: '/path/to/pubspec.yaml',
+            kind: DependencyKind.normal,
+            isTransitive: false,
+          ),
+        ],
+        doUpgrade: false,
+      );
+      final YamlMap pubspec = loadYaml(pubspecSource) as YamlMap;
+      expect((pubspec['dependencies'] as YamlMap)['foo'], prevVersion);
+    });
+  });
 }
 
 class FakePub extends Fake implements Pub {