radiance · commit

Fix `if let` binding scope in else branches

7fec22301c94093f5e4cd520e0c0fe87c6d9217de6b10818eabc896f351e5a18

`if let` lowering left successful pattern bindings in the variable
lookup scope while lowering the else branch. A same-named outer
variable was shadowed by a success-only binding there, producing
undefined SSA values and runtime traps.

Restore the pre-pattern variable scope before lowering the else branch
while preserving values needed by the successful path and merge block.

Alexis Sellier committed 23 days ago 1 parent d5a7e016

lib/std/lang/lower.rad +4 -1

    try lowerPatternMatch(self, &subject, &cond.pattern, &mut thenBlock, "then", elseBlock);

    // Lower then branch.
    try lowerNode(self, cond.thenBranch);
    try emitMergeIfUnterminated(self, &mut mergeBlock);
    // Pattern bindings are visible only in the success branch. Restore the
    // outer variable scope before lowering `else`, where a same-named outer
    // variable may be referenced.
    exitVarScope(self, savedVarsLen);

    // Lower else branch.
    try switchToAndSeal(self, elseBlock);
    if let elseBranch = cond.elseBranch {
        try lowerNode(self, elseBranch);

    try emitMergeIfUnterminated(self, &mut mergeBlock);

    if let blk = mergeBlock {
        try switchToAndSeal(self, blk);
    }
    exitVarScope(self, savedVarsLen);
}

/// Emit pattern match branch with optional guard, and bind variables.
/// Used by `if-let`, `let-else`, and `while-let` lowering.
///

test/tests/iflet.shadow.else.rad added +18 -0

1	+	//! returns: 0
2	+	//! An if-let pattern binding only shadows an outer variable in the success
3	+	//! branch; the else branch must still read the outer SSA value.
4	+
5	+	fn choose(value: ?i32) -> i32 {
6	+	let outer: i32 = 7;
7	+	if let outer = value {
8	+	return outer;
9	+	} else {
10	+	return outer;
11	+	}
12	+	}
13	+
14	+	@default fn main() -> i32 {
15	+	assert choose(41) == 41;
16	+	assert choose(nil) == 7;
17	+	return 0;
18	+	}

3777	3777		try lowerPatternMatch(self, &subject, &cond.pattern, &mut thenBlock, "then", elseBlock);
3778	3778
3779	3779		// Lower then branch.
3780	3780		try lowerNode(self, cond.thenBranch);
3781	3781		try emitMergeIfUnterminated(self, &mut mergeBlock);
	3782	+	// Pattern bindings are visible only in the success branch. Restore the
	3783	+	// outer variable scope before lowering `else`, where a same-named outer
	3784	+	// variable may be referenced.
	3785	+	exitVarScope(self, savedVarsLen);
3782	3786
3783	3787		// Lower else branch.
3784	3788		try switchToAndSeal(self, elseBlock);
3785	3789		if let elseBranch = cond.elseBranch {
3786	3790		try lowerNode(self, elseBranch);

3788	3792		try emitMergeIfUnterminated(self, &mut mergeBlock);
3789	3793
3790	3794		if let blk = mergeBlock {
3791	3795		try switchToAndSeal(self, blk);
3792	3796		}
3793		-	exitVarScope(self, savedVarsLen);
3794	3797		}
3795	3798
3796	3799		/// Emit pattern match branch with optional guard, and bind variables.
3797	3800		/// Used by `if-let`, `let-else`, and `while-let` lowering.
3798	3801		///