Report error for assignment in if condition
#42649
Conversation
|
r? @pnkfelix (rust_highfive has picked a reviewer for you, use r? to override) |
|
The "expected bool, found ()" message was kinda educational - "it's not like assignments are special and can't be used in some contexts, it's just the result has inappropriate type". |
|
☔ The latest upstream changes (presumably #42644) made this pull request unmergeable. Please resolve the merge conflicts. |
aidanhs
added
the
S-waiting-on-review
For code like `if x = 3 {}`, output:
```
error[E0308]: mismatched types
--> $DIR/issue-17283.rs:25:8
|
25 | if x = x {
| ^^^^^
| |
| help: did you mean to compare equality? `x == x`
| expected bool, found ()
|
= note: expected type `bool`
found type `()`
```
|
@petrochenkov changed |
src/librustc_typeck/check/mod.rs
Outdated
| let rhs_ty = self.check_expr_coercable_to_type(&rhs, lhs_ty); | ||
|
|
||
| match expected { | ||
| ExpectIfCondition => (), |
There was a problem hiding this comment.
This makes me mildly nervous. Can you add a call like self.tcx.sess.delay_span_bug(lhs.span, "invalid lhs expression in if; expected error elsehwere")? That way, in case there is some edge condition, compilation will abort and not just succeed.
src/librustc_typeck/check/mod.rs
Outdated
| self.check_expr_expect_type(expr, ExpectHasType(expected)) | ||
| } | ||
|
|
||
| fn check_expr_expect_type(&self, |
There was a problem hiding this comment.
Maybe we can call this check_expr_meets_expectation_or_error? I think this zoo of functions is sort of confusing, and the existing naming convention isn't the clearest (for bonus points, we could apply the _or_error convention elsewhere, e.g. check_expr_has_type_or_error)
src/librustc_typeck/check/mod.rs
Outdated
| @@ -341,6 +344,7 @@ impl<'a, 'gcx, 'tcx> Expectation<'tcx> { | |||
| fn only_has_type(self, fcx: &FnCtxt<'a, 'gcx, 'tcx>) -> Option<Ty<'tcx>> { | |||
| match self.resolve(fcx) { | |||
| ExpectHasType(ty) => Some(ty), | |||
| ExpectIfCondition => Some(fcx.tcx.types.bool), | |||
| _ => None | |||
There was a problem hiding this comment.
Nit: Pre-existing, but I'd rather this match were exhaustive.
src/librustc_typeck/check/demand.rs
Outdated
| self.demand_suptype_diag(sp, expected, actual).map(|mut e| e.emit()); | ||
| } | ||
|
|
||
| pub fn demand_suptype_diag(&self, sp: Span, |
There was a problem hiding this comment.
Nit, formatting: can you move the sp to the next line so it's easier to see how many arguments this function takes?
| @@ -24,25 +24,25 @@ fn main() { | |||
| // `x { ... }` should not be interpreted as a struct literal here | |||
There was a problem hiding this comment.
This isn't really a 'regression test for obscure scenario'. Let's rename the test to assignment-in-if.rs. While we're at it, can you add some other obscure cases, like this one:
if (if true { x = 4 } else { x = 5 }) { ... }I don't really care what message it emits, although I think (if I read the code right...) that the expectation will be propagated. I just wanted to test it.
| @@ -45,4 +45,9 @@ fn main() { | |||
| //~| HELP did you mean to compare equality? | |||
| println!("{}", x); | |||
| } | |||
| if (if true { x = 4 } else { x = 5 }) { | |||
| //~^ ERROR mismatched types | |||
| //~| HELP did you mean to compare equality? | |||
There was a problem hiding this comment.
Nit: we are not (currently) checking these annotations in ui tests (I want to...), but it doesn't appear that we emit a HELP in this case?
- exhaustive match - rename method to `check_expr_meets_expectation_or_error` - formatting - add `delay_span_bug` - add test
|
@bors r=nikomatsakis |
|
📌 Commit da78b4d has been approved by |
Report error for assignment in `if` condition
For code like `if x = 3 {}`, output:
```
error[E0308]: mismatched types
--> $DIR/issue-17283.rs:25:8
|
25 | if x = x {
| ^^^^^
| |
| help: did you mean to compare equality? `x == x`
| expected bool, found ()
|
= note: expected type `bool`
found type `()`
```
Fix #40926.
|
☀️ Test successful - status-appveyor, status-travis |
For code like
if x = 3 {}, output:Fix #40926.