Looks like meson now requires a newer ninja than what ships with whatever version of whatever Debian-derived distribution Azure Pipelines uses. Use ninja from pip instead (it's a special distribution maintained by the SciPy guys, apparently).

azure-pipelines.yml

@@ -23,8 +23,8 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
-  - template: azure-pipelines/linux-386-install-gtk-dev-ninja.yml
+  - template: azure-pipelines/linux-386-install-gtk-dev.yml
   - template: azure-pipelines/configure.yml
     parameters:
       beforeConfigure: export CFLAGS=-m32 CXXFLAGS=-m32 PKG_CONFIG_PATH=/usr/lib/i386-linux-gnu/pkgconfig
@@ -46,8 +46,8 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
-  - template: azure-pipelines/linux-386-install-gtk-dev-ninja.yml
+  - template: azure-pipelines/linux-386-install-gtk-dev.yml
   - template: azure-pipelines/configure.yml
     parameters:
       beforeConfigure: export CFLAGS=-m32 CXXFLAGS=-m32 PKG_CONFIG_PATH=/usr/lib/i386-linux-gnu/pkgconfig
@@ -69,8 +69,8 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
-  - template: azure-pipelines/linux-install-gtk-dev-ninja.yml
+  - template: azure-pipelines/linux-install-gtk-dev.yml
   - template: azure-pipelines/configure.yml
     parameters:
       defaultLibrary: shared
@@ -91,8 +91,8 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
-  - template: azure-pipelines/linux-install-gtk-dev-ninja.yml
+  - template: azure-pipelines/linux-install-gtk-dev.yml
   - template: azure-pipelines/configure.yml
     parameters:
       defaultLibrary: static
@@ -117,7 +117,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/vs2015-install-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/windows-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -143,7 +143,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/vs2015-install-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/windows-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -170,7 +170,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/vs2015-install-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/windows-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -196,7 +196,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/vs2015-install-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/windows-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -227,7 +227,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/windows-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -253,7 +253,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/windows-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -280,7 +280,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/windows-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -306,7 +306,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/windows-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -339,7 +339,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/darwin-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:
@@ -361,7 +361,7 @@ jobs:
     clean: all
   steps:
   - template: azure-pipelines/setup-python3.yml
-  - template: azure-pipelines/install-latest-meson.yml
+  - template: azure-pipelines/install-latest-meson-ninja.yml
   - template: azure-pipelines/darwin-install-ninja.yml
   - template: azure-pipelines/configure.yml
     parameters:

azure-pipelines/TODOMatrix

@@ -25,7 +25,7 @@ strategy:
       libtype: 'shared'
       vmImage: 'ubuntu-16.04'
       python3Template: 'azure-pipelines/setup-python3.yml'
-      depsAndNinjaTemplate: 'azure-pipelines/linux-386-install-gtk-dev-ninja.yml'
+      depsAndNinjaTemplate: 'azure-pipelines/linux-386-install-gtk-dev.yml'
       beforeConfigure: 'export CFLAGS=-m32 CXXFLAGS=-m32 PKG_CONFIG_PATH=/usr/lib/i386-linux-gnu/pkgconfig'
       artifactTemplate: 'azure-pipelines/artifacts.yml'
       libfiles: 'libui.so.0'
@@ -39,7 +39,7 @@ workspace:
 
 steps:
 - template: $(variables.python3Template)
-- template: azure-pipelines/install-latest-meson.yml
+- template: azure-pipelines/install-latest-meson-ninja.yml
 - template: $(variables.depsAndNinjaTemplate)
 - template: azure-pipelines/configure.yml
   parameters:
@@ -67,8 +67,8 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
-#  - template: azure-pipelines/linux-386-install-gtk-dev-ninja.yml
+#  - template: azure-pipelines/linux-386-install-gtk-dev.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
 #      beforeConfigure: export CFLAGS=-m32 CXXFLAGS=-m32 PKG_CONFIG_PATH=/usr/lib/i386-linux-gnu/pkgconfig
@@ -90,8 +90,8 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
-#  - template: azure-pipelines/linux-install-gtk-dev-ninja.yml
+#  - template: azure-pipelines/linux-install-gtk-dev.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
 #      defaultLibrary: shared
@@ -112,8 +112,8 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
-#  - template: azure-pipelines/linux-install-gtk-dev-ninja.yml
+#  - template: azure-pipelines/linux-install-gtk-dev.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
 #      defaultLibrary: static
@@ -138,7 +138,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/vs2015-install-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/windows-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -164,7 +164,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/vs2015-install-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/windows-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -191,7 +191,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/vs2015-install-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/windows-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -217,7 +217,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/vs2015-install-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/windows-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -248,7 +248,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/windows-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -274,7 +274,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/windows-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -301,7 +301,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/windows-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -327,7 +327,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/windows-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -360,7 +360,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/darwin-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:
@@ -382,7 +382,7 @@ steps:
 #    clean: all
 #  steps:
 #  - template: azure-pipelines/setup-python3.yml
-#  - template: azure-pipelines/install-latest-meson.yml
+#  - template: azure-pipelines/install-latest-meson-ninja.yml
 #  - template: azure-pipelines/darwin-install-ninja.yml
 #  - template: azure-pipelines/configure.yml
 #    parameters:

azure-pipelines/collapsed

@@ -102,10 +102,10 @@
 - template: azure-pipelines/setup-python3.yml
 - template: azure-pipelines/vs2015-install-python3.yml
 }
-- template: azure-pipelines/install-latest-meson.yml
+- template: azure-pipelines/install-latest-meson-ninja.yml
 {
-- template: azure-pipelines/linux-386-install-gtk-dev-ninja.yml
+- template: azure-pipelines/linux-386-install-gtk-dev.yml
-- template: azure-pipelines/linux-install-gtk-dev-ninja.yml
+- template: azure-pipelines/linux-install-gtk-dev.yml
 - template: azure-pipelines/windows-install-ninja.yml
 - template: azure-pipelines/darwin-install-ninja.yml
 }

azure-pipelines/install-latest-meson-ninja.yml

@@ -0,0 +1,9 @@
+# 4 april 2019
+
+# TODO remove ninja installation from non-Linux OSs and make the same ninja via pip change in the AppVeyor script
+
+steps:
+- script: |
+    python -m pip install --upgrade pip setuptools wheel
+    pip install meson ninja
+  displayName: 'Install Latest Meson and Ninja'

azure-pipelines/install-latest-meson.yml

@@ -1,7 +0,0 @@
-# 4 april 2019
-
-steps:
-- script: |
-    python -m pip install --upgrade pip setuptools wheel
-    pip install meson
-  displayName: 'Install Latest Meson'

azure-pipelines/linux-386-install-gtk-dev.yml

@@ -13,5 +13,5 @@ steps:
     sudo apt-get install --allow-downgrades \
       gcc-multilib g++-multilib \
       $llvmPackages \
-      libgtk-3-dev:i386 ninja-build
+      libgtk-3-dev:i386
-  displayName: 'Install GTK+ Dev Files and Ninja'
+  displayName: 'Install GTK+ Dev Files'

azure-pipelines/linux-install-gtk-dev-ninja.yml

@@ -1,6 +0,0 @@
-# 7 april 2019
-
-steps:
-- script: |
-    sudo apt-get install libgtk-3-dev ninja-build
-  displayName: 'Install GTK+ Dev Files and Ninja'

azure-pipelines/linux-install-gtk-dev.yml

@@ -0,0 +1,6 @@
+# 7 april 2019
+
+steps:
+- script: |
+    sudo apt-get install libgtk-3-dev
+  displayName: 'Install GTK+ Dev Files'