Merge pull request #605 from mesonbuild/ternary

Added ternary operator support

mesonbuild/interpreter.py

@@ -1323,6 +1323,8 @@ class Interpreter():
             return self.evaluate_plusassign(cur)
         elif isinstance(cur, mparser.IndexNode):
             return self.evaluate_indexing(cur)
+        elif isinstance(cur, mparser.TernaryNode):
+            return self.evaluate_ternary(cur)
         elif self.is_elementary_type(cur):
             return cur
         else:
@@ -2402,6 +2404,16 @@ class Interpreter():
         if not isinstance(node.elseblock, mparser.EmptyNode):
             self.evaluate_codeblock(node.elseblock)
 
+    def evaluate_ternary(self, node):
+        assert(isinstance(node, mparser.TernaryNode))
+        result = self.evaluate_statement(node.condition)
+        if not isinstance(result, bool):
+            raise InterpreterException('Ternary condition is not boolean.')
+        if result:
+            return self.evaluate_statement(node.trueblock)
+        else:
+            return self.evaluate_statement(node.falseblock)
+
     def evaluate_foreach(self, node):
         assert(isinstance(node, mparser.ForeachClauseNode))
         varname = node.varname.value

mesonbuild/mparser.py

@@ -67,6 +67,7 @@ class Lexer:
             ('lt', re.compile(r'<')),
             ('ge', re.compile(r'>=')),
             ('gt', re.compile(r'>')),
+            ('questionmark', re.compile(r'\?')),
         ]
 
     def lex(self, code):
@@ -282,6 +283,14 @@ class IfNode():
         self.condition = condition
         self.block = block
 
+class TernaryNode():
+    def __init__(self, lineno, colno, condition, trueblock, falseblock):
+        self.lineno = lineno
+        self.colno = colno
+        self.condition = condition
+        self.trueblock = trueblock
+        self.falseblock = falseblock
+
 class ArgumentNode():
     def __init__(self, token):
         self.lineno = token.lineno
@@ -344,6 +353,7 @@ class Parser:
     def __init__(self, code):
         self.stream = Lexer().lex(code)
         self.getsym()
+        self.in_ternary = False
 
     def getsym(self):
         try:
@@ -383,6 +393,16 @@ class Parser:
                 raise ParseException('Assignment target must be an id.',
                                      left.lineno, left.colno)
             return AssignmentNode(left.lineno, left.colno, left.value, value)
+        elif self.accept('questionmark'):
+            if self.in_ternary:
+                raise ParseException('Nested ternary operators are not allowed.',
+                                     left.lineno, left.colno)
+            self.in_ternary = True
+            trueblock = self.e1()
+            self.expect('colon')
+            falseblock = self.e1()
+            self.in_ternary = False
+            return TernaryNode(left.lineno, left.colno, left, trueblock, falseblock)
         return left
 
     def e2(self):

test cases/common/116 ternary/meson.build

@@ -0,0 +1,7 @@
+project('ternary operator', 'c')
+
+one = true ? 1 : error('False branch should not be evaluated')
+two = false ? error('True branch should not be evaluated.') : 2
+
+assert(one == 1, 'Return value from ternary true is wrong.')
+assert(two == 2, 'Return value from ternary false is wrong.')

test cases/failing/30 nested ternary/meson.build

@@ -0,0 +1,3 @@
+project('nested ternary', 'c')
+
+x = true ? (false ? 1 : 0) : 2