Make equality, comparison and 'in' operators not associative.
I'm not using a --incompatible-change flag because it's not available in the
parser. We could pass it, but I think this is trivial to fix and unlikely to
happen in real code (if it does, there was most likely a bug).
RELNOTES[INC]:
Operators for equality, comparison, 'in' and 'not in' are no longer associative,
e.g. x < y < z is now a syntax error. Before, it was parsed as: (x < y) < z.
PiperOrigin-RevId: 159422042
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Parser.java b/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
index ed23432..46de9a9 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Parser.java
@@ -950,6 +950,7 @@
Expression expr = parseNonTupleExpression(prec + 1);
// The loop is not strictly needed, but it prevents risks of stack overflow. Depth is
// limited to number of different precedence levels (operatorPrecedence.size()).
+ Operator lastOp = null;
for (;;) {
if (token.kind == TokenKind.NOT) {
@@ -967,10 +968,21 @@
if (!operatorPrecedence.get(prec).contains(operator)) {
return expr;
}
+
+ // Operator '==' and other operators of the same precedence (e.g. '<', 'in')
+ // are not associative.
+ if (lastOp != null && operatorPrecedence.get(prec).contains(Operator.EQUALS_EQUALS)) {
+ reportError(
+ lexer.createLocation(token.left, token.right),
+ String.format("Operator '%s' is not associative with operator '%s'. Use parens.",
+ lastOp, operator));
+ }
+
nextToken();
Expression secondary = parseNonTupleExpression(prec + 1);
expr = optimizeBinOpExpression(operator, expr, secondary);
setLocation(expr, start, secondary);
+ lastOp = operator;
}
}
