Merge pull request matplotlib#13084 from anntzer/use-upstream-libpng-zlib-windows-names

BLD: When linking against libpng/zlib on Windows, use upstream lib names.

Author: tacaswell

.appveyor.yml

@@ -77,8 +77,8 @@ install:
   # Let the install prefer the static builds of the libs
   - set LIBRARY_LIB=%CONDA_PREFIX%\Library\lib
   - mkdir lib || cmd /c "exit /b 0"
-  - copy /y %LIBRARY_LIB%\zlibstatic.lib lib\z.lib
-  - copy /y %LIBRARY_LIB%\libpng_static.lib lib\png.lib
+  - copy /y %LIBRARY_LIB%\zlibstatic.lib lib\zlib.lib
+  - copy /y %LIBRARY_LIB%\libpng16_static.lib lib\libpng16.lib
   # These z.lib / png.lib are not static versions but files which end up as
   # dependencies to the dll file. This is fine for the conda build, but not here
   # and for the wheels

build_alllocal.cmd

@@ -20,8 +20,8 @@ IF NOT DEFINED CONDA_PREFIX (
 :: copy the libs which have "wrong" names
 set LIBRARY_LIB=%CONDA_PREFIX%\Library\lib
 mkdir lib || cmd /c "exit /b 0"
-copy %LIBRARY_LIB%\zlibstatic.lib lib\z.lib
-copy %LIBRARY_LIB%\libpng_static.lib lib\png.lib
+copy %LIBRARY_LIB%\zlibstatic.lib lib\zlib.lib
+copy %LIBRARY_LIB%\libpng16_static.lib lib\libpng16.lib
 
 :: build the target
 python setup.py %TARGET%

doc/api/next_api_changes/2019-01-02-AL.rst

@@ -0,0 +1,19 @@
+Changes to the Windows build
+````````````````````````````
+
+Previously, when building the :mod:`matplotlib._png` extension, the build
+script would add "png" and "z" to the extensions ``.libraries`` attribute (if
+pkg-config information is not available, which is in particular the case on
+Windows).
+
+In particular, this implies that the Windows build would look up files named
+``png.lib`` and ``z.lib``; but neither libpng upstream nor zlib upstream
+provides these files by default.  (On Linux, this would look up ``libpng.so``
+and ``libz.so``, which are indeed standard names.)
+
+Instead, on Windows, we now look up ``libpng16.lib`` and ``zlib.lib``, which
+*are* the upstream names for the shared libraries (as of libpng 1.6.x).
+
+For a statically-linked build, the upstream names are ``libpng16_static.lib``
+and ``zlibstatic.lib``; one still needs to manually rename them if such a build
+is desired.

setupext.py

@@ -650,7 +650,13 @@ def get_extension(self):
             ext, 'libpng',
             atleast_version='1.2',
             alt_exec=['libpng-config', '--ldflags'],
-            default_libraries=['png', 'z'])
+            default_libraries=(
+                ['png', 'z'] if os.name == 'posix' else
+                # libpng upstream names their lib libpng16.lib, not png.lib.
+                # zlib upstream names their lib zlib.lib, not z.lib.
+                ['libpng16', 'zlib'] if os.name == 'nt' else
+                []
+            ))
         add_numpy_flags(ext)
         return ext