%pyproject_buildrequires: Fallback to setuptools.build_meta:__legacy__ only if setup.py exists

Fixes: rhbz#1976459

Related: rhbz#1950291

macros.pyproject

@@ -97,10 +97,13 @@ echo 'python%{python3_pkgversion}dist(pip) >= 19'
 echo 'python%{python3_pkgversion}dist(packaging)'
 %{!-N:if [ -f pyproject.toml ]; then
   echo 'python%{python3_pkgversion}dist(toml)'
-else
+elif [ -f setup.py ]; then
   # Note: If the default requirements change, also change them in the script!
   echo 'python%{python3_pkgversion}dist(setuptools) >= 40.8'
   echo 'python%{python3_pkgversion}dist(wheel)'
+else
+  echo 'ERROR: Neither pyproject.toml nor setup.py found, consider using %%%%pyproject_buildrequires -N <requirements-file> if this is not a Python package.' >&2
+  exit 1
 fi}
 # Check if we can generate dependencies on Python extras
 if [ "%{py_dist_name []}" == "[]" ]; then

pyproject-rpm-macros.spec

@@ -110,9 +110,10 @@ export HOSTNAME="rpmbuild"  # to speedup tox in network-less mock, see rhbz#1856
 %license LICENSE
 
 %changelog
-* Fri Jul 09 2021 Miro Hrončok <miro@hroncok.cz> - 0-44
+* Fri Jul 09 2021 Python Maint <python-maint@redhat.com> - 0-44
 - Escape weird paths generated by %%pyproject_save_files
 - Support x.* versions in %%pyproject_buildrequires
+- %%pyproject_buildrequires fallbacks to setuptools only if setup.py exists
 - Rebuilt for IMA sigs, glibc 2.34, aarch64 flags
   Related: rhbz#1991688
 

pyproject_buildrequires.py

@@ -181,6 +181,10 @@ def get_backend(requirements):
         # missing, the source tree is not using this specification, and tools
         # should revert to the legacy behaviour of running setup.py
         # (either directly, or by implicitly invoking the [following] backend).
+        # If setup.py is also not present program will mimick pip's behavior
+        # and end with an error.
+        if not os.path.exists('setup.py'):
+            raise FileNotFoundError('File "setup.py" not found for legacy project.')
         backend_name = 'setuptools.build_meta:__legacy__'
 
         # Note: For projects without pyproject.toml, this was already echoed

pyproject_buildrequires_testcases.yaml

@@ -1,10 +1,7 @@
 No pyproject.toml, nothing installed:
   installed:
     # empty
-  expected: |
-    python3dist(setuptools) >= 40.8
-    python3dist(wheel)
-  result: 0
+  except: FileNotFoundError
 
 Nothing installed yet:
   installed:
@@ -14,7 +11,7 @@ Nothing installed yet:
   expected: |
     python3dist(setuptools) >= 40.8
     python3dist(wheel)
-  result: 0
+  except: FileNotFoundError
 
 Insufficient version of setuptools:
   installed:
@@ -23,6 +20,7 @@ Insufficient version of setuptools:
     toml: 1
   pyproject.toml: |
     # empty
+  setup.py: |
   expected: |
     python3dist(setuptools) >= 40.8
     python3dist(wheel)
@@ -53,6 +51,24 @@ Default build system, empty setup.py:
     python3dist(wheel)
   result: 0
 
+pyproject.toml with build-backend and setup.py:
+  generate_extras: true
+  installed:
+    setuptools: 50
+    wheel: 1
+    toml: 1
+  setup.py: |
+    # empty
+  pyproject.toml: |
+    [build-system]
+    requires = [
+        "foo",
+    ]
+    build-backend = "foo.build"
+  expected: |
+    python3dist(foo)
+  result: 0
+
 Erroring setup.py:
   installed:
     setuptools: 50
@@ -74,7 +90,8 @@ Single value version with unsupported compatible operator:
     toml: 1
   pyproject.toml: |
     [build-system]
-    requires = ["pkg ~= 42"]
+    requires = ["pkg ~= 42", "foo"]
+    build-backend = "foo.build"
   stderr_contains: "WARNING: Skipping invalid requirement: pkg ~= 42"
   result: 0
 
@@ -83,7 +100,8 @@ Asterisk in version with unsupported compatible operator:
     toml: 1
   pyproject.toml: |
     [build-system]
-    requires = ["pkg ~= 0.1.*"]
+    requires = ["pkg ~= 0.1.*", "foo"]
+    build-backend = "foo.build"
   stderr_contains: "WARNING: Skipping invalid requirement: pkg ~= 0.1.*"
   result: 0
 
@@ -113,6 +131,7 @@ Build system dependencies in pyproject.toml with extras:
         "py2 ; python_version < '2.7'",
         "py3 ; python_version > '3.0'",
     ]
+    build-backend = "foo.build"
   expected: |
     python3dist(foo)
     python3dist(bar) > 5
@@ -131,8 +150,6 @@ Build system dependencies in pyproject.toml with extras:
     python3dist(multi[extras2]) = 6
     ((python3dist(combo) < 3 or python3dist(combo) > 3) with python3dist(combo) < 5 with python3dist(combo) > 2)
     python3dist(py3)
-    python3dist(setuptools) >= 40.8
-    python3dist(wheel)
   result: 0
 
 Build system dependencies in pyproject.toml without extras:
@@ -147,11 +164,10 @@ Build system dependencies in pyproject.toml without extras:
         "bar[Baz] > 5",
         "multi[extras1,extras2] == 6.0",
     ]
+    build-backend = "foo.build"
   expected: |
     python3dist(bar) > 5
     python3dist(multi) = 6
-    python3dist(setuptools) >= 40.8
-    python3dist(wheel)
   result: 0
 
 Default build system, build dependencies in setup.py: