From c1ce7534e3ae0d02e82234a3736678d11c95651d Mon Sep 17 00:00:00 2001
From: finswimmer <finswimmer77@gmail.com>
Date: Wed, 22 Jan 2025 06:50:53 +0100
Subject: [PATCH] feat(cli): ensure build-system is defined when running poetry
 build

---
 src/poetry/console/commands/build.py               |  9 +++++++++
 tests/console/commands/test_build.py               | 14 ++++++++++++++
 .../build_systems/no_build_system/README.md        |  2 ++
 .../build_systems/no_build_system/pyproject.toml   | 11 +++++++++++
 .../no_build_system/simple_project/__init__.py     |  0
 5 files changed, 36 insertions(+)
 create mode 100644 tests/fixtures/build_systems/no_build_system/README.md
 create mode 100644 tests/fixtures/build_systems/no_build_system/pyproject.toml
 create mode 100644 tests/fixtures/build_systems/no_build_system/simple_project/__init__.py

diff --git a/src/poetry/console/commands/build.py b/src/poetry/console/commands/build.py
index 0bc293b1e16..976b21c6ddd 100644
--- a/src/poetry/console/commands/build.py
+++ b/src/poetry/console/commands/build.py
@@ -114,6 +114,9 @@ def _get_builder(self) -> Callable[..., None]:
 
         return self._build
 
+    def _has_build_system_defined(self) -> bool:
+        return "build-system" in self.poetry.file.read()
+
     def build(self, options: BuildOptions) -> int:
         if not self.poetry.is_package_mode:
             self.io.write_error_line(
@@ -121,6 +124,12 @@ def build(self, options: BuildOptions) -> int:
             )
             return 1
 
+        if not self._has_build_system_defined():
+            self.io.write_error_line(
+                "No build-system defined. Please define one in pyproject.toml."
+            )
+            return 1
+
         dist_dir = Path(options.output)
         package = self.poetry.package
         self.io.write_line(
diff --git a/tests/console/commands/test_build.py b/tests/console/commands/test_build.py
index 18b57a3bf25..9efd00b0ed0 100644
--- a/tests/console/commands/test_build.py
+++ b/tests/console/commands/test_build.py
@@ -300,3 +300,17 @@ def test_build_handler_build_isolated(
     handler.build(BuildOptions(clean=True, formats=["wheel"], output="dist"))
 
     assert mock_builder.build.call_count == 1
+
+
+def test_build_handler_raise_on_no_build_system(
+    fixture_dir: FixtureDirGetter,
+    command_tester_factory: CommandTesterFactory,
+) -> None:
+    poetry = Factory().create_poetry(fixture_dir("build_systems/no_build_system"))
+    tester = command_tester_factory("build", poetry)
+
+    assert tester.execute() == 1
+    assert (
+        tester.io.fetch_error()
+        == "No build-system defined. Please define one in pyproject.toml.\n"
+    )
diff --git a/tests/fixtures/build_systems/no_build_system/README.md b/tests/fixtures/build_systems/no_build_system/README.md
new file mode 100644
index 00000000000..f7fe15470f9
--- /dev/null
+++ b/tests/fixtures/build_systems/no_build_system/README.md
@@ -0,0 +1,2 @@
+My Package
+==========
diff --git a/tests/fixtures/build_systems/no_build_system/pyproject.toml b/tests/fixtures/build_systems/no_build_system/pyproject.toml
new file mode 100644
index 00000000000..946593d6093
--- /dev/null
+++ b/tests/fixtures/build_systems/no_build_system/pyproject.toml
@@ -0,0 +1,11 @@
+[project]
+name = "core-from-git"
+version = "1.2.3"
+description = "Some description."
+authors = [
+    { name = "Poetry Contributors", email = "no-reply@python-poetry.org" }
+]
+license = { text = "MIT" }
+readme = "README.md"
+keywords = ["packaging", "dependency", "poetry"]
+requires-python = ">=3.4"
diff --git a/tests/fixtures/build_systems/no_build_system/simple_project/__init__.py b/tests/fixtures/build_systems/no_build_system/simple_project/__init__.py
new file mode 100644
index 00000000000..e69de29bb2d