Allow `dart pub add` with existing package, update constraint instead of adding (#3570)

lib/src/command/add.dart

diff --git a/lib/src/command/add.dart b/lib/src/command/add.dart
index 78b1e5d..15b64a4 100644
--- a/lib/src/command/add.dart
+++ b/lib/src/command/add.dart
@@ -213,11 +213,10 @@
     final range =
         package.ref.withConstraint(package.constraint ?? VersionConstraint.any);
     if (isDev) {
-      /// TODO(walnut): Change the error message once pub upgrade --bump is
-      /// released
       if (devDependencyNames.contains(name)) {
-        dataError('"$name" is already in "dev_dependencies". '
-            'Use "pub upgrade $name" to upgrade to a later version!');
+        log.message('"$name" is already in "dev_dependencies". '
+            'Will try to update the constraint.');
+        devDependencies.removeWhere((element) => element.name == name);
       }
 
       /// If package is originally in dependencies and we wish to add it to
@@ -232,11 +231,10 @@
 
       devDependencies.add(range);
     } else {
-      /// TODO(walnut): Change the error message once pub upgrade --bump is
-      /// released
       if (dependencyNames.contains(name)) {
-        dataError('"$name" is already in "dependencies". '
-            'Use "pub upgrade $name" to upgrade to a later version!');
+        log.message(
+            '"$name" is already in "dependencies". Will try to update the constraint.');
+        dependencies.removeWhere((element) => element.name == name);
       }
 
       /// If package is originally in dev_dependencies and we wish to add it to
@@ -245,7 +243,7 @@
       if (devDependencyNames.contains(name)) {
         log.message('"$name" was found in dev_dependencies. '
             'Removing "$name" and adding it to dependencies instead.');
-        devDependencies = devDependencies.where((d) => d.name != name).toList();
+        devDependencies.removeWhere((element) => element.name == name);
       }
 
       dependencies.add(range);

test/add/common/add_test.dart

diff --git a/test/add/common/add_test.dart b/test/add/common/add_test.dart
index f1e76a7..25f9d8d 100644
--- a/test/add/common/add_test.dart
+++ b/test/add/common/add_test.dart
@@ -185,7 +185,7 @@
       await d.appDir({'foo': '1.2.3'}).validate();
     });
 
-    group('warns user to use pub upgrade if package exists', () {
+    group('notifies user about existing constraint', () {
       test('if package is added without a version constraint', () async {
         await servePackages()
           ..serve('foo', '1.2.3')
@@ -194,13 +194,13 @@
         await d.appDir({'foo': '1.2.2'}).create();
 
         await pubAdd(
-            args: ['foo'],
-            exitCode: exit_codes.DATA,
-            error:
-                contains('"foo" is already in "dependencies". Use "pub upgrade '
-                    'foo" to upgrade to a later version!'));
+          args: ['foo'],
+          output: contains(
+            '"foo" is already in "dependencies". Will try to update the constraint.',
+          ),
+        );
 
-        await d.appDir({'foo': '1.2.2'}).validate();
+        await d.appDir({'foo': '^1.2.3'}).validate();
       });
 
       test('if package is added with a specific version constraint', () async {
@@ -211,13 +211,13 @@
         await d.appDir({'foo': '1.2.2'}).create();
 
         await pubAdd(
-            args: ['foo:1.2.3'],
-            exitCode: exit_codes.DATA,
-            error:
-                contains('"foo" is already in "dependencies". Use "pub upgrade '
-                    'foo" to upgrade to a later version!'));
+          args: ['foo:1.2.3'],
+          output: contains(
+            '"foo" is already in "dependencies". Will try to update the constraint.',
+          ),
+        );
 
-        await d.appDir({'foo': '1.2.2'}).validate();
+        await d.appDir({'foo': '1.2.3'}).validate();
       });
 
       test('if package is added with a version constraint range', () async {
@@ -229,12 +229,10 @@
 
         await pubAdd(
             args: ['foo:>=1.2.2'],
-            exitCode: exit_codes.DATA,
-            error:
-                contains('"foo" is already in "dependencies". Use "pub upgrade '
-                    'foo" to upgrade to a later version!'));
+            output: contains(
+                '"foo" is already in "dependencies". Will try to update the constraint.'));
 
-        await d.appDir({'foo': '1.2.2'}).validate();
+        await d.appDir({'foo': '>=1.2.2'}).validate();
       });
     });
 
@@ -517,7 +515,7 @@
       ]).validate();
     });
 
-    group('warns user to use pub upgrade if package exists', () {
+    group('notifies user if package exists', () {
       test('if package is added without a version constraint', () async {
         await servePackages()
           ..serve('foo', '1.2.3')
@@ -532,15 +530,13 @@
 
         await pubAdd(
             args: ['foo', '--dev'],
-            exitCode: exit_codes.DATA,
-            error: contains(
-                '"foo" is already in "dev_dependencies". Use "pub upgrade '
-                'foo" to upgrade to a later version!'));
+            output: contains(
+                '"foo" is already in "dev_dependencies". Will try to update the constraint.'));
 
         await d.dir(appPath, [
           d.pubspec({
             'name': 'myapp',
-            'dev_dependencies': {'foo': '1.2.2'}
+            'dev_dependencies': {'foo': '^1.2.3'}
           })
         ]).validate();
       });
@@ -559,15 +555,13 @@
 
         await pubAdd(
             args: ['foo:1.2.3', '--dev'],
-            exitCode: exit_codes.DATA,
-            error: contains(
-                '"foo" is already in "dev_dependencies". Use "pub upgrade '
-                'foo" to upgrade to a later version!'));
+            output: contains(
+                '"foo" is already in "dev_dependencies". Will try to update the constraint.'));
 
         await d.dir(appPath, [
           d.pubspec({
             'name': 'myapp',
-            'dev_dependencies': {'foo': '1.2.2'}
+            'dev_dependencies': {'foo': '1.2.3'}
           })
         ]).validate();
       });
@@ -586,15 +580,13 @@
 
         await pubAdd(
             args: ['foo:>=1.2.2', '--dev'],
-            exitCode: exit_codes.DATA,
-            error: contains(
-                '"foo" is already in "dev_dependencies". Use "pub upgrade '
-                'foo" to upgrade to a later version!'));
+            output: contains(
+                '"foo" is already in "dev_dependencies". Will try to update the constraint.'));
 
         await d.dir(appPath, [
           d.pubspec({
             'name': 'myapp',
-            'dev_dependencies': {'foo': '1.2.2'}
+            'dev_dependencies': {'foo': '>=1.2.2'}
           })
         ]).validate();
       });