Add support to integer modulo operator

Having support for the '%' operator makes it easier to implement
even/odd version checks, like:

    enable_debug = get_option('enable-debug')
    if enable_debug == 'auto'
      if minor_version % 2 == 0
        enable_debug = 'minimum'
      else
        enable_debug = 'yes'
      endif
    endif

which would be impossible without resorting to less obvious long-hand
forms like:

  a - (b * (a / b))

3 files changed, 15 insertions, 1 deletions

diff --git a/mesonbuild/interpreter.py b/mesonbuild/interpreter.py
index ac95e15..535a3f0 100644
--- a/mesonbuild/interpreter.py
+++ b/mesonbuild/interpreter.py
@@ -2595,6 +2595,10 @@ class Interpreter():
             if not isinstance(l, int) or not isinstance(r, int):
                 raise InvalidCode('Division works only with integers.')
             return l // r
+        elif cur.operation == 'mod':
+            if not isinstance(l, int) or not isinstance(r, int):
+                raise InvalidCode('Modulo works only with integers.')
+            return l % r
         else:
             raise InvalidCode('You broke me.')
 
diff --git a/mesonbuild/mparser.py b/mesonbuild/mparser.py
index 2f0eb2d..f593c8e 100644
--- a/mesonbuild/mparser.py
+++ b/mesonbuild/mparser.py
@@ -58,6 +58,7 @@ class Lexer:
             ('plus', re.compile(r'\+')),
             ('dash', re.compile(r'-')),
             ('star', re.compile(r'\*')),
+            ('percent', re.compile(r'\%')),
             ('fslash', re.compile(r'/')),
             ('colon', re.compile(r':')),
             ('equal', re.compile(r'==')),
@@ -434,11 +435,17 @@ class Parser:
         return left
 
     def e5sub(self):
-        left = self.e5mul()
+        left = self.e5mod()
         if self.accept('dash'):
             return ArithmeticNode(left.lineno, left.colno, 'sub', left, self.e5sub())
         return left
 
+    def e5mod(self):
+        left = self.e5mul()
+        if self.accept('percent'):
+            return ArithmeticNode(left.lineno, left.colno, 'mod', left, self.e5mod())
+        return left
+
     def e5mul(self):
         left = self.e5div()
         if self.accept('star'):
diff --git a/test cases/common/68 number arithmetic/meson.build b/test cases/common/68 number arithmetic/meson.build
index 4b98d73..1bc8155 100644
--- a/test cases/common/68 number arithmetic/meson.build
+++ b/test cases/common/68 number arithmetic/meson.build
@@ -21,6 +21,9 @@ if (5 / 3) * 3 != 3
   error('Integer division is broken')
 endif
 
+assert((5 % 2) == 1, 'Integer modulo (odd) is broken')
+assert((4 % 2) == 0, 'Integer modulo (even) is broken')
+
 assert(3 < 4, 'Lt broken')
 assert(not(4 < 3), 'Lt broken')
 assert(3 <= 4, 'Lte broken')