Fails to build with Python 3.8

[sebastic]

As reported by Gianfranco Costamagna in Debian Bug #949864:

Hello, when built on experimental, the python3-config command needs a new flag to find correctly the python3.8 library (thanks Doko for the suggestion)

so, the following (unfortunately non-retro-compatible) patch, fixes the issue:

--- qgis-3.4.15+dfsg/debian/changelog 2020-01-22 05:57:39.000000000 +0100
+++ qgis-3.4.15+dfsg/debian/changelog 2020-01-25 22:17:14.000000000 +0100
@@ -1,3 +1,10 @@
+qgis (3.4.15+dfsg-1.1) experimental; urgency=medium
+
+  * Manually add --embed to rules file to fix FTBFS due to change in
+    behaviour of python3-config --ldflags (from doko) (Closes: #-1)
+
+ -- Gianfranco Costamagna <locutusofborg@debian.org>  Sat, 25 Jan 2020 22:17:14 +0100
+
 qgis (3.4.15+dfsg-1) unstable; urgency=medium

   * Move from experimental to unstable.
diff -Nru qgis-3.4.15+dfsg/debian/rules qgis-3.4.15+dfsg/debian/rules
--- qgis-3.4.15+dfsg/debian/rules     2019-11-11 09:07:24.000000000 +0100
+++ qgis-3.4.15+dfsg/debian/rules     2020-01-25 22:17:14.000000000 +0100
@@ -93,7 +93,7 @@
      -DWITH_SERVER_PLUGINS=TRUE \
      -DWITH_QWTPOLAR=FALSE \
      -DQT_PLUGINS_DIR=$(QT_PLUGINS_DIR) \
-     -DPYTHON_LIBRARY=$(shell python3-config --ldflags | sed -e 's\#-L\(.*\) -L/usr/lib -l\([^ ]*\) .*$$\#\1/lib\2.so\#')
+     -DPYTHON_LIBRARY=$(shell python3-config --ldflags --embed | sed -e 's\#-L\(.*\) -L/usr/lib -l\([^ ]*\) .*$$\#\1/lib\2.so\#')

 ifneq ($(SHA),)
      CMAKE_OPTS += -DSHA=$(SHA)

To make the suggested patch work with older Python as well, the following change was applied to the Debian package:

--- a/debian/rules
+++ b/debian/rules
@@ -57,6 +57,8 @@ GRASS=grass$(subst .,,$(shell pkg-config --modversion grass|cut -d. -f1,2))
 GRASSVER=$(subst .,,$(shell pkg-config --modversion grass|cut -d. -f1))
 GRASSABI=$(subst .,,$(shell pkg-config --modversion grass|cut -d. -f1,2,3|sed -e 's/RC/-/'))
 
+PYTHON_GE_38=$(shell python3 -c 'import sys; print(1) if(sys.version_info[0] > 3 or (sys.version_info[0] == 3 and sys.version_info[1] >= 8)) else print(0)')
+
 # Include percentage of started edges
 export NINJA_STATUS=[%f/%t %p]
 
@@ -92,8 +94,13 @@ CMAKE_OPTS := \
        -DWITH_SERVER=TRUE \
        -DWITH_SERVER_PLUGINS=TRUE \
        -DWITH_QWTPOLAR=FALSE \
-       -DQT_PLUGINS_DIR=$(QT_PLUGINS_DIR) \
-       -DPYTHON_LIBRARY=$(shell python3-config --ldflags | sed -e 's\#-L\(.*\) -L/usr/lib -l\([^ ]*\) .*$$\#\1/lib\2.so\#')
+       -DQT_PLUGINS_DIR=$(QT_PLUGINS_DIR)
+
+ifeq ($(PYTHON_GE_38),1)
+       CMAKE_OPTS += -DPYTHON_LIBRARY=$(shell python3-config --ldflags --embed | sed -e 's\#-L\(.*\) -L/usr/lib -l\([^ ]*\) .*$$\#\1/lib\2.so\#')
+else
+       CMAKE_OPTS += -DPYTHON_LIBRARY=$(shell python3-config --ldflags | sed -e 's\#-L\(.*\) -L/usr/lib -l\([^ ]*\) .*$$\#\1/lib\2.so\#')
+endif
 
 ifneq ($(SHA),)
        CMAKE_OPTS += -DSHA=$(SHA)

[roya0045]

Still valid?

[sebastic]

3.10.3 hardcoded /usr/lib/x86_64-linux-gnu/libpython3.8.so, 3.10.4 contains a change similar to the one in the Debian package mentioned above, except that it uses the distribution to decide whether to use the --embed option instead of checking for Python >= 3.8.