feat(commands/add): canonicalize package name when looking for existing packages

src/poetry/console/commands/add.py

@@ -9,6 +9,8 @@ from cleo.helpers import argument
 from cleo.helpers import option
 from tomlkit.toml_document import TOMLDocument
 
+from poetry.utils.helpers import canonicalize_name
+
 
 try:
     from poetry.core.packages.dependency_group import MAIN_GROUP
@@ -268,7 +270,7 @@ You can specify a package in the following forms:
 
         for name in packages:
             for key in section:
-                if key.lower() == name.lower():
+                if canonicalize_name(key) == canonicalize_name(name):
                     existing_packages.append(name)
 
         return existing_packages

tests/console/commands/test_add.py

@@ -940,6 +940,30 @@ If you prefer to upgrade it to the latest available version,\
     assert expected in tester.io.fetch_output()
 
 
+def test_add_should_skip_when_adding_canonicalized_existing_package_with_no_constraint(
+    app: PoetryTestApplication, repo: TestRepository, tester: CommandTester
+):
+    content = app.poetry.file.read()
+    content["tool"]["poetry"]["dependencies"]["foo-bar"] = "^1.0"
+    app.poetry.file.write(content)
+
+    repo.add_package(get_package("foo-bar", "1.1.2"))
+    tester.execute("Foo_Bar")
+
+    expected = """\
+The following packages are already present in the pyproject.toml and will be skipped:
+
+  • Foo_Bar
+
+If you want to update it to the latest compatible version,\
+ you can use `poetry update package`.
+If you prefer to upgrade it to the latest available version,\
+ you can use `poetry add package@latest`.
+"""
+
+    assert expected in tester.io.fetch_output()
+
+
 def test_add_should_work_when_adding_existing_package_with_latest_constraint(
     app: PoetryTestApplication, repo: TestRepository, tester: CommandTester
 ):