mlog: set LESS environment variable for pager.

Rather than passing arguments directly to less, set the LESS environment
variable to contain the desired arguments instead. This allows passing
arguments in case the user has PAGER=less set in their environment.

mesonbuild/mlog.py

@@ -421,17 +421,23 @@ def start_pager() -> None:
                 path = Path(git).parents[1] / 'usr' / 'bin'
                 less = shutil.which('less', path=str(path))
         if less:
-            # "R" : support color
-            # "X" : do not clear the screen when leaving the pager
-            # "F" : skip the pager if content fit into the screen
-            pager_cmd = [less, '-RXF']
+            pager_cmd = [less]
     if not pager_cmd:
         return
     global log_pager # pylint: disable=global-statement
     assert log_pager is None
     try:
+        # Set 'LESS' environment variable, rather than arguments in
+        # pager_cmd, to also support the case where the user has 'PAGER'
+        # set to 'less'. Arguments set are:
+        # "R" : support color
+        # "X" : do not clear the screen when leaving the pager
+        # "F" : skip the pager if content fits into the screen
+        env = os.environ.copy()
+        if 'LESS' not in env:
+            env['LESS'] = 'RXF'
         log_pager = subprocess.Popen(pager_cmd, stdin=subprocess.PIPE,
-                                     text=True, encoding='utf-8')
+                                     text=True, encoding='utf-8', env=env)
     except Exception as e:
         # Ignore errors, unless it is a user defined pager.
         if 'PAGER' in os.environ: