Improve error message about upper Flint cap

Author: oscarbenjamin

meson.build

@@ -1,5 +1,17 @@
 project('python-flint', 'cython', 'c')
 
+py = import('python').find_installation(pure: false)
+dep_py = py.dependency()
+
+cc = meson.get_compiler('c')
+
+flint_ver_lower = '3.0' # >=3.0
+flint_ver_upper = '3.2' # <3.2
+
+gmp_dep = dependency('gmp')
+mpfr_dep = dependency('mpfr')
+flint_dep = dependency('flint', version: ['>=' + flint_ver_lower])
+
 #
 # For the source release, we should by default fail for newer versions of Flint
 # that are untested with a nice error message:
@@ -13,20 +25,31 @@ project('python-flint', 'cython', 'c')
 # that future versions of Flint will not work.
 #
 if get_option('flint_version_check')
-  flint_version_required = ['>=3.0', '<3.2']
-else
-  # We do know that Flint < 3.0 will not work so no point allowing it.
-  flint_version_required = ['>=3.0']
-endif
+  if flint_dep.version().version_compare('>=' + flint_ver_upper)
+    error('''
 
-py = import('python').find_installation(pure: false)
-dep_py = py.dependency()
+      Invalid Flint version:
+      Version needed is: @0@ <= flint < @1@
+      Version found is: flint == @2@
 
-cc = meson.get_compiler('c')
+      By default, python-flint will only build against Flint versions that have
+      been tested. If you are sure you want to use this version of Flint, you
+      can disable this check with -Dflint_version_check=false.
 
-gmp_dep = dependency('gmp')
-mpfr_dep = dependency('mpfr')
-flint_dep = dependency('flint', version: flint_version_required)
+      If building from the source directory using meson directly, you can do
+      this with:
+
+        meson setup build -Dflint_version_check=false
+
+      If you are installing with pip, you can do this with:
+
+        pip install --config-settings=setup-args="-Dflint_version_check=false" python-flint
+
+      Other build frontends have similar options for passing this to meson.
+      '''.format(flint_ver_lower, flint_ver_upper, flint_dep.version())
+    )
+  endif
+endif
 
 add_project_arguments(
     '-X', 'embedsignature=True',