parser: allow whitespaces and comments in cont_eol

FIXME: another approach would be to consider cont_eol as comment (i.e.
add backslash and whitespaces to the comment regex). In both cases it
works until we want to parse comments separately.

TODO?: handle eol_cont inside a string (to split long string without
breaking lines). Probably a bad idea and better to simply join a
multiline string.

mesonbuild/mparser.py

@@ -121,7 +121,7 @@ class Lexer:
             ('fstring', re.compile(r"f'([^'\\]|(\\.))*'")),
             ('id', re.compile('[_a-zA-Z][_0-9a-zA-Z]*')),
             ('number', re.compile(r'0[bB][01]+|0[oO][0-7]+|0[xX][0-9a-fA-F]+|0|[1-9]\d*')),
-            ('eol_cont', re.compile(r'\\\n')),
+            ('eol_cont', re.compile(r'\\[ \t]*(#.*)?\n')),
             ('eol', re.compile(r'\n')),
             ('multiline_string', re.compile(r"'''(.|\n)*?'''", re.M)),
             ('comment', re.compile(r'#.*')),

test cases/unit/118 rewrite/meson.build

@@ -173,12 +173,12 @@ no_string_escapes = '''\\\'\a\b\f\n\r\t\v\046\x26\u2D4d\U00002d4d\N{GREEK CAPITA
 # cont_string = 'blablabla\
 # blablabla'
 
-# FIXME: is it supposed to work? (cont_eol with whitespace and comments after)
-# if a \  # comment in cont 1
-#     and b \  # comment in cont 2
-#     or c  # comment in cont 3
-#   message('ok')
-# endif
+# cont_eol with whitespace and comments after
+if a \  # comment in cont 1
+    and b \  # comment in cont 2
+    or c  # comment in cont 3
+  message('ok')
+endif
 
 if a \
     or b