Fix MSBuild property for VS2019+ Current layout and instance-derived install dir

setuptools/msvc.py

@@ -504,6 +504,13 @@ def VSInstallDir(self) -> str:
         str
             path
         """
+        # Prefer the exact installation path recorded by the Visual Studio
+        # installer instance state (VS2017+), which avoids the lossy
+        # major.minor float formatting of ``vs_ver`` (e.g. 17.12 -> "17.1").
+        for ver, path in sorted(self.known_vs_paths.items(), reverse=True):
+            if int(ver) == int(self.vs_ver):
+                return path
+
         # Default path
         default = os.path.join(
             self.ProgramFilesx86, f'Microsoft Visual Studio {self.vs_ver:0.1f}'
@@ -1333,14 +1340,24 @@ def MSBuild(self):
             base_path = self.si.VSInstallDir
             arch_subdir = ''
 
-        path = rf'MSBuild\{self.vs_ver:0.1f}\bin{arch_subdir}'
-        build = [os.path.join(base_path, path)]
+        if self.vs_ver < 15.0:
+            path = rf'MSBuild\{self.vs_ver:0.1f}\bin{arch_subdir}'
+            build = [os.path.join(base_path, path)]
+        elif self.vs_ver < 16.0:
+            # Visual Studio 2017 keeps the per-version layout.
+            path = rf'MSBuild\{self.vs_ver:0.1f}\bin'
+            build = [os.path.join(base_path, path)]
+        else:
+            # Since Visual Studio 2019 (v16), MSBuild lives under a
+            # version-independent "Current" directory instead of
+            # "MSBuild\<version>".
+            path = r'MSBuild\Current\bin'
+            build = [os.path.join(base_path, path)]
 
-        if self.vs_ver >= 15.0:
             # Add Roslyn C# & Visual Basic Compiler
             build += [os.path.join(base_path, path, 'Roslyn')]
 
-        return build
+        return [p for p in build if os.path.isdir(p)] or build
 
     @property
     def HTMLHelpWorkshop(self):

setuptools/tests/test_msvc_msbuild.py

@@ -0,0 +1,143 @@
+"""Tests for the MSBuild property of EnvironmentInfo (issue #5275)."""
+
+import os
+
+import pytest
+
+from ..msvc import EnvironmentInfo
+
+
+class FakePlatformInfo:
+    def current_dir(self, hidex86=False):
+        return '' if hidex86 else '\\x86'
+
+
+class FakeRegistryInfo:
+    def __init__(self, pi, vs_install_dir=None):
+        self.pi = pi
+        self._vs_install_dir = vs_install_dir
+        self.vs = 'vs'
+
+    def lookup(self, key, version):
+        return self._vs_install_dir
+
+
+def make_env(
+    monkeypatch,
+    tmp_path,
+    vs_ver,
+    vs_install_dir=None,
+    known_vs_paths=None,
+    program_filesx86='C:\\Program Files (x86)',
+):
+    """Build an EnvironmentInfo whose filesystem view is rooted at tmp_path."""
+
+    real_isdir = os.path.isdir
+
+    def fake_isdir(path):
+        path = str(path)
+        if path.startswith('C:\\'):
+            # Translate synthetic absolute paths into the temp tree.
+            rel = path[3:]
+            return real_isdir(os.path.join(tmp_path, rel))
+        return real_isdir(path)
+
+    env = object.__new__(EnvironmentInfo)
+    fake_si = type('SI', (), {})()
+    fake_si.vs_ver = vs_ver
+    fake_si.ProgramFilesx86 = program_filesx86
+    fake_si.VSInstallDir = (
+        vs_install_dir
+        if vs_install_dir is not None
+        else os.path.join(
+            program_filesx86, f'Microsoft Visual Studio {vs_ver:0.1f}'
+        )
+    )
+    env.si = fake_si
+    env.known_vs_paths = dict(known_vs_paths or {})
+    env.ri = FakeRegistryInfo(FakePlatformInfo())
+    env.pi = env.ri.pi
+    monkeypatch.setattr(os.path, 'isdir', fake_isdir)
+    return env
+
+
+class TestMSBuildProperty:
+    def test_vs2019_and_later_use_current_layout(self, monkeypatch, tmp_path):
+        """VS2019+ (v16+) must use the version-independent Current layout."""
+        env = make_env(monkeypatch, tmp_path, 16.0)
+        paths = env.MSBuild
+        assert paths == [
+            os.path.join(env.si.VSInstallDir, r'MSBuild\Current\bin'),
+            os.path.join(env.si.VSInstallDir, r'MSBuild\Current\bin', 'Roslyn'),
+        ]
+
+    def test_vs2022_multiline_version_gets_current_layout(
+        self, monkeypatch, tmp_path
+    ):
+        """Regression for #5275: vs_ver like 17.12/18.7 must not fall back to a
+        per-version directory that never exists on VS2019+ installs."""
+        env = make_env(monkeypatch, tmp_path, 17.12)
+        paths = env.MSBuild
+        assert all(r'MSBuild\17.1\bin' not in p for p in paths)
+        assert any(r'MSBuild\Current\bin' in p for p in paths)
+
+    def test_vs2026_uses_current_layout(self, monkeypatch, tmp_path):
+        env = make_env(monkeypatch, tmp_path, 18.7)
+        paths = env.MSBuild
+        assert any(r'MSBuild\Current\bin' in p for p in paths)
+        assert not any(r'MSBuild\18.' in p for p in paths)
+
+    def test_vs2015_keeps_legacy_layout(self, monkeypatch, tmp_path):
+        """VS2015 and earlier keep the historical per-version layout."""
+        env = make_env(monkeypatch, tmp_path, 14.0)
+        paths = env.MSBuild
+        assert paths == [
+            os.path.join('C:\\Program Files (x86)', r'MSBuild\14.0\bin')
+        ]
+
+    def test_vs2017_keeps_per_version_layout(self, monkeypatch, tmp_path):
+        """VS2017 (15.x) keeps the per-version layout under VSInstallDir."""
+        env = make_env(monkeypatch, tmp_path, 15.9)
+        paths = env.MSBuild
+        assert [p for p in paths if not p.endswith('\\Roslyn')] == [
+            os.path.join(env.si.VSInstallDir, r'MSBuild\15.9\bin')
+        ]
+
+    def test_too_old_returns_empty(self, monkeypatch, tmp_path):
+        env = make_env(monkeypatch, tmp_path, 11.0)
+        assert env.MSBuild == []
+
+    def test_nonexistent_candidates_are_filtered_only_if_alternatives_exist(
+        self, monkeypatch, tmp_path
+    ):
+        """When no candidate directory exists on disk, the raw candidates are
+        returned unchanged; when Current exists it wins and Roslyn follows."""
+        current_bin = tmp_path / r'MSBuild\Current\bin'
+        current_bin.mkdir(parents=True)
+
+        env = make_env(monkeypatch, tmp_path, 17.12, vs_install_dir='C:\\VS')
+        paths = env.MSBuild
+        assert paths == [
+            'C:\\VS\\MSBuild\\Current\\bin',
+            'C:\\VS\\MSBuild\\Current\\bin\\Roslyn',
+        ]
+
+        # Nothing exists -> unfiltered candidates are returned.
+        current_bin.rmdir()
+        env2 = make_env(monkeypatch, tmp_path, 17.12, vs_install_dir='C:\\VS')
+        assert env2.MSBuild == [
+            'C:\\VS\\MSBuild\\Current\\bin',
+            'C:\\VS\\MSBuild\\Current\\bin\\Roslyn',
+        ]
+
+    @pytest.mark.skipif(os.name != 'nt', reason="Windows-only behaviour")
+    def test_real_environment_returns_existing_paths(self):
+        """On a machine with a real VS install, every returned path exists."""
+        try:
+            env = EnvironmentInfo('amd64')
+        except Exception:
+            pytest.skip("No MSVC installation detected")
+        if env.vs_ver < 15.0:
+            pytest.skip("Legacy VS layout installed")
+        for path in env.MSBuild:
+            assert os.path.isdir(path), f"Nonexistent MSBuild path: {path}"