Be stricter when detecting Windows/Cygwin

This removes the check for "mingw" for platform.system(). The only case I know
where "mingw" is return is if using a msys Python under a msys2 mingw environment.
This combination is not really supported by meson and will result in weird errors,
so remove the check.

The second change is checking sys.platform for cygwin instead of platform.system().
The former is document to return "cygwin", while the latter is not and just
returns uname().

While under Cygwin it uname() always starts with "cygwin" it's not hardcoded in MSYS2
and starts with the environment name. Using sys.platform is safer here.

Fixes #7552

5 files changed, 9 insertions, 11 deletions

diff --git a/mesonbuild/envconfig.py b/mesonbuild/envconfig.py
index 9402d38de..5258fa077 100644
--- a/mesonbuild/envconfig.py
+++ b/mesonbuild/envconfig.py
@@ -211,13 +211,13 @@ class MachineInfo:
         """
         Machine is windows?
         """
-        return self.system == 'windows' or 'mingw' in self.system
+        return self.system == 'windows'
 
     def is_cygwin(self) -> bool:
         """
         Machine is cygwin?
         """
-        return self.system.startswith('cygwin')
+        return self.system == 'cygwin'
 
     def is_linux(self) -> bool:
         """
diff --git a/mesonbuild/environment.py b/mesonbuild/environment.py
index f1bd2e107..eb7189c50 100644
--- a/mesonbuild/environment.py
+++ b/mesonbuild/environment.py
@@ -429,10 +429,9 @@ def detect_cpu(compilers: CompilersDict):
     return trial
 
 def detect_system():
-    system = platform.system().lower()
-    if system.startswith('cygwin'):
+    if sys.platform == 'cygwin':
         return 'cygwin'
-    return system
+    return platform.system().lower()
 
 def detect_msys2_arch():
     if 'MSYSTEM_CARCH' in os.environ:
diff --git a/mesonbuild/mesonlib.py b/mesonbuild/mesonlib.py
index 45e3b34ad..a510ab9af 100644
--- a/mesonbuild/mesonlib.py
+++ b/mesonbuild/mesonlib.py
@@ -502,11 +502,11 @@ def is_openbsd() -> bool:
 
 def is_windows() -> bool:
     platname = platform.system().lower()
-    return platname == 'windows' or 'mingw' in platname
+    return platname == 'windows'
 
 
 def is_cygwin() -> bool:
-    return platform.system().lower().startswith('cygwin')
+    return sys.platform == 'cygwin'
 
 
 def is_debianlike() -> bool:
diff --git a/mesonbuild/mtest.py b/mesonbuild/mtest.py
index d7fe54ad8..de82234d4 100644
--- a/mesonbuild/mtest.py
+++ b/mesonbuild/mtest.py
@@ -58,11 +58,10 @@ GNU_ERROR_RETURNCODE = 99
 
 def is_windows() -> bool:
     platname = platform.system().lower()
-    return platname == 'windows' or 'mingw' in platname
+    return platname == 'windows'
 
 def is_cygwin() -> bool:
-    platname = platform.system().lower()
-    return 'cygwin' in platname
+    return sys.platform == 'cygwin'
 
 def determine_worker_count() -> int:
     varname = 'MESON_TESTTHREADS'
diff --git a/test cases/common/215 link custom/custom_stlib.py b/test cases/common/215 link custom/custom_stlib.py
index 0157fb14c..6a090f3db 100755
--- a/test cases/common/215 link custom/custom_stlib.py
+++ b/test cases/common/215 link custom/custom_stlib.py
@@ -18,7 +18,7 @@ void flob(void) {
 
 def get_pic_args():
     platname = platform.system().lower()
-    if platname in ['windows', 'mingw', 'darwin'] or platname.startswith('cygwin'):
+    if platname in ['windows', 'darwin'] or sys.platform == 'cygwin':
         return []
     return ['-fPIC']