Ninja not found even when in path

[habersaa]

Describe the bug While trying to build gstream from the gst-build repository, at some point meson fails with the message "ERROR: Could not detect Ninja v1.5 or newer"

But Ninja is correctly in the path: PS C:\work\tests\gst-build> which ninja /c/Users/alexandre.haabersat/AppData/Roaming/Python/Python38/Scripts/ninja

PS C:\work\tests\gst-build> ninja --version 1.9.0.git.kitware.dyndep-1.jobserver-1

I have tried with 3 different versions of ninja, but the same problem appears all the time.

To Reproduce

1. Clone gst-build from the github repository https://github.com/GStreamer/gst-build
2. Navigate to the base of the repository (with a PowerShell contains MSVC compiler configuration).
3. Type "meson build"

4. All subproject are checked out correctly, but at the end it fails with a message saying that ninja is not found:

   
   All GStreamer modules 1.17.0.1
   
   Subprojects
                       FFmpeg: YES 3 warnings
                        dssim: NO C library 'm' not found
                   gl-headers: YES
                         glib: YES 3 warnings
                     graphene: YES
                 gst-devtools: YES
         gst-editing-services: YES
                 gst-examples: YES
   gst-integration-testsuites: YES
                    gst-libav: YES
                      gst-omx: NO Feature 'omx' disabled
              gst-plugins-bad: YES 3 warnings
             gst-plugins-base: YES 4 warnings
             gst-plugins-good: YES 5 warnings
               gst-plugins-rs: NO Feature 'rs' disabled
             gst-plugins-ugly: YES 1 warnings
                   gst-python: NO Could not find dependency pygobject_dep in subproject pygobject
              gst-rtsp-server: YES
                    gstreamer: YES 1 warnings
              gstreamer-sharp: NO Feature 'sharp' disabled
              gstreamer-vaapi: NO Feature 'vaapi' disabled
                        gtest: NO Subproject directory not found and gtest.wrap file not found
                    json-glib: YES 3 warnings
                       libffi: YES
                  libmicrodns: YES
                      libnice: NO Problem encountered: Either GnuTLS or OpenSSL is required as crypto library, but neither was found
                       libpsl: YES
                      libsoup: NO [WinError 2] The system cannot find the file specified
                      libxml2: YES
                     openh264: YES 8 warnings
                      openssl: NO Subproject directory not found and openssl.wrap file not found
                          orc: YES
                proxy-libintl: YES
                    pygobject: NO Subproject directory not found and gobject-introspection.wrap file not found
                       sqlite: YES
                     tinyalsa: NO Subproject directory not found and tinyalsa.wrap file not found
      win-flex-bison-binaries: YES
                     win-nasm: YES
                         x264: YES
                         zlib: YES

ERROR: Could not detect Ninja v1.5 or newer

This is very frustrating as Ninja is correctly in the PATH, this error message is wrong and I see no way to overcome this error.

**Expected behavior**
4. Everything should be checked out and built by meson with no error.

**system parameters**
* Is this a [cross build](https://mesonbuild.com/Cross-compilation.html) or just a plain native build (for the same computer)?
Native Windows 10 build with MSVC19 64-bits.
* what operating system (e.g. MacOS Catalina, Windows 10, CentOS 8.0, Ubuntu 18.04, etc.)
Windows 10
* what Python version are you using e.g. 3.8.0
3.8.2-32, installed from the windows installer on the website
* what `meson --version`
0.54.1, installed with pip3
* what `ninja --version` if it's a Ninja build
1.9.0.git.kitware.dyndep-1.jobserver-1, installed with pip3
Also tried 1.10.0 from officiel repo binaries
Also tried 1.9.0 from Qt installation
Also tried from MSVC installation
(Only one Ninja is in the Windows path at a time.)

[habersaa]

After checking the python code of meson, I found a work-around for this issue by defining an environment variable called "NINJA" with the exact path, but neither the "ninja.exe" located in the Windows path, nor the one located beside meson.exe (when installed with Python) have been found.

[dreamer-coding]

Hello, @habersaa I think if you install Ninja with the pip package manager it would start working. Conceder reading through this page for more on that.