From d54432288eb091ecfc4eab6c7c90d29149975706 Mon Sep 17 00:00:00 2001
From: layday <layday@protonmail.com>
Date: Fri, 2 Sep 2022 23:01:39 +0300
Subject: [PATCH] build: add circular dependency protection

Fixes  #511.
---
 src/build/__init__.py        | 13 ++++++++++---
 tests/test_projectbuilder.py | 10 +++++-----
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/src/build/__init__.py b/src/build/__init__.py
index ea534b3d8..80f19a121 100644
--- a/src/build/__init__.py
+++ b/src/build/__init__.py
@@ -176,6 +176,11 @@ def check_dependency(
         import importlib_metadata
 
     req = packaging.requirements.Requirement(req_string)
+    normalised_req_string = str(req)
+
+    if normalised_req_string in ancestral_req_strings:
+        # cyclical dependency, already checked.
+        return
 
     if req.marker:
         extras = frozenset(('',)).union(parent_extras)
@@ -190,15 +195,17 @@ def check_dependency(
         dist = importlib_metadata.distribution(req.name)  # type: ignore[no-untyped-call]
     except importlib_metadata.PackageNotFoundError:
         # dependency is not installed in the environment.
-        yield ancestral_req_strings + (req_string,)
+        yield ancestral_req_strings + (normalised_req_string,)
     else:
         if req.specifier and not req.specifier.contains(dist.version, prereleases=True):
             # the installed version is incompatible.
-            yield ancestral_req_strings + (req_string,)
+            yield ancestral_req_strings + (normalised_req_string,)
         elif dist.requires:
             for other_req_string in dist.requires:
                 # yields transitive dependencies that are not satisfied.
-                yield from check_dependency(other_req_string, ancestral_req_strings + (req_string,), req.extras)
+                yield from check_dependency(
+                    other_req_string, ancestral_req_strings + (normalised_req_string,), req.extras
+                )
 
 
 def _find_typo(dictionary: Mapping[str, str], expected: str) -> None:
diff --git a/tests/test_projectbuilder.py b/tests/test_projectbuilder.py
index 5988cbb0a..d5b1bdf30 100644
--- a/tests/test_projectbuilder.py
+++ b/tests/test_projectbuilder.py
@@ -133,24 +133,24 @@ def read_text(self, filename):
         ('extras_dep[extra_without_associated_deps]', None),
         (
             'extras_dep[extra_with_unmet_deps]',
-            ('extras_dep[extra_with_unmet_deps]', "unmet_dep; extra == 'extra_with_unmet_deps'"),
+            ('extras_dep[extra_with_unmet_deps]', 'unmet_dep; extra == "extra_with_unmet_deps"'),
         ),
         (
             'extras_dep[recursive_extra_with_unmet_deps]',
             (
                 'extras_dep[recursive_extra_with_unmet_deps]',
-                "recursive_dep; extra == 'recursive_extra_with_unmet_deps'",
+                'recursive_dep; extra == "recursive_extra_with_unmet_deps"',
                 'recursive_unmet_dep',
             ),
         ),
         ('extras_dep[extra_with_met_deps]', None),
         ('missing_dep; python_version>"10"', None),
         ('missing_dep; python_version<="1"', None),
-        ('missing_dep; python_version>="1"', ('missing_dep; python_version>="1"',)),
+        ('missing_dep; python_version>="1"', ('missing_dep; python_version >= "1"',)),
         ('extras_dep == 1.0.0', None),
-        ('extras_dep == 2.0.0', ('extras_dep == 2.0.0',)),
+        ('extras_dep == 2.0.0', ('extras_dep==2.0.0',)),
         ('extras_dep[extra_without_associated_deps] == 1.0.0', None),
-        ('extras_dep[extra_without_associated_deps] == 2.0.0', ('extras_dep[extra_without_associated_deps] == 2.0.0',)),
+        ('extras_dep[extra_without_associated_deps] == 2.0.0', ('extras_dep[extra_without_associated_deps]==2.0.0',)),
         ('prerelease_dep >= 1.0.0', None),
         ('circular_dep', None),
     ],