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Rollup merge of rust-lang#64049 - estebank:if-else-type-err, r=Centril
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Emit a single error on if expr with expectation and no else clause

Fix rust-lang#60254.

r? @Centril
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@Centril
Centril committed Sep 1, 2019
2 parents e29faf0 + f53c217 commit f45ad8d
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Showing 5 changed files with 30 additions and 105 deletions.
30 changes: 21 additions & 9 deletions src/librustc_typeck/check/_match.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -112,19 +112,26 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}

self.diverges.set(pats_diverge);
let arm_ty = self.check_expr_with_expectation(&arm.body, expected);
let arm_ty = if source_if && if_no_else && i != 0 && self.if_fallback_coercion(
expr.span,
&arms[0].body,
&mut coercion,
) {
tcx.types.err
} else {
// Only call this if this is not an `if` expr with an expected type and no `else`
// clause to avoid duplicated type errors. (#60254)
self.check_expr_with_expectation(&arm.body, expected)
};
all_arms_diverge &= self.diverges.get();

let span = expr.span;

if source_if {
let then_expr = &arms[0].body;
match (i, if_no_else) {
(0, _) => coercion.coerce(self, &self.misc(span), &arm.body, arm_ty),
(_, true) => self.if_fallback_coercion(span, then_expr, &mut coercion),
(0, _) => coercion.coerce(self, &self.misc(expr.span), &arm.body, arm_ty),
(_, true) => {} // Handled above to avoid duplicated type errors (#60254).
(_, _) => {
let then_ty = prior_arm_ty.unwrap();
let cause = self.if_cause(span, then_expr, &arm.body, then_ty, arm_ty);
let cause = self.if_cause(expr.span, then_expr, &arm.body, then_ty, arm_ty);
coercion.coerce(self, &cause, &arm.body, arm_ty);
}
}
Expand All @@ -139,7 +146,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
// The reason for the first arm to fail is not that the match arms diverge,
// but rather that there's a prior obligation that doesn't hold.
0 => (arm_span, ObligationCauseCode::BlockTailExpression(arm.body.hir_id)),
_ => (span, ObligationCauseCode::MatchExpressionArm {
_ => (expr.span, ObligationCauseCode::MatchExpressionArm {
arm_span,
source: match_src,
prior_arms: other_arms.clone(),
Expand Down Expand Up @@ -180,16 +187,19 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}

/// Handle the fallback arm of a desugared if(-let) like a missing else.
///
/// Returns `true` if there was an error forcing the coercion to the `()` type.
fn if_fallback_coercion(
&self,
span: Span,
then_expr: &'tcx hir::Expr,
coercion: &mut CoerceMany<'tcx, '_, rustc::hir::Arm>,
) {
) -> bool {
// If this `if` expr is the parent's function return expr,
// the cause of the type coercion is the return type, point at it. (#25228)
let ret_reason = self.maybe_get_coercion_reason(then_expr.hir_id, span);
let cause = self.cause(span, ObligationCauseCode::IfExpressionWithNoElse);
let mut error = false;
coercion.coerce_forced_unit(self, &cause, &mut |err| {
if let Some((span, msg)) = &ret_reason {
err.span_label(*span, msg.as_str());
Expand All @@ -200,7 +210,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
}
err.note("`if` expressions without `else` evaluate to `()`");
err.help("consider adding an `else` block that evaluates to the expected type");
error = true;
}, ret_reason.is_none());
error
}

fn maybe_get_coercion_reason(&self, hir_id: hir::HirId, span: Span) -> Option<(Span, String)> {
Expand Down
6 changes: 0 additions & 6 deletions src/test/ui/if/if-without-else-as-fn-expr.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -3,15 +3,13 @@ fn foo(bar: usize) -> usize {
return 3;
}
//~^^^ ERROR if may be missing an else clause
//~| ERROR mismatched types [E0308]
}

fn foo2(bar: usize) -> usize {
let x: usize = if bar % 5 == 0 {
return 3;
};
//~^^^ ERROR if may be missing an else clause
//~| ERROR mismatched types [E0308]
x
}

Expand All @@ -20,23 +18,20 @@ fn foo3(bar: usize) -> usize {
3
}
//~^^^ ERROR if may be missing an else clause
//~| ERROR mismatched types [E0308]
}

fn foo_let(bar: usize) -> usize {
if let 0 = 1 {
return 3;
}
//~^^^ ERROR if may be missing an else clause
//~| ERROR mismatched types [E0308]
}

fn foo2_let(bar: usize) -> usize {
let x: usize = if let 0 = 1 {
return 3;
};
//~^^^ ERROR if may be missing an else clause
//~| ERROR mismatched types [E0308]
x
}

Expand All @@ -45,7 +40,6 @@ fn foo3_let(bar: usize) -> usize {
3
}
//~^^^ ERROR if may be missing an else clause
//~| ERROR mismatched types [E0308]
}

// FIXME(60254): deduplicate first error in favor of second.
Expand Down
83 changes: 7 additions & 76 deletions src/test/ui/if/if-without-else-as-fn-expr.stderr
View file
Original file line number Diff line number Diff line change
@@ -1,14 +1,3 @@
error[E0308]: mismatched types
--> $DIR/if-without-else-as-fn-expr.rs:2:5
|
LL | / if bar % 5 == 0 {
LL | | return 3;
LL | | }
| |_____^ expected usize, found ()
|
= note: expected type `usize`
found type `()`

error[E0317]: if may be missing an else clause
--> $DIR/if-without-else-as-fn-expr.rs:2:5
|
Expand All @@ -24,20 +13,8 @@ LL | | }
= note: `if` expressions without `else` evaluate to `()`
= help: consider adding an `else` block that evaluates to the expected type

error[E0308]: mismatched types
--> $DIR/if-without-else-as-fn-expr.rs:10:20
|
LL | let x: usize = if bar % 5 == 0 {
| ____________________^
LL | | return 3;
LL | | };
| |_____^ expected usize, found ()
|
= note: expected type `usize`
found type `()`

error[E0317]: if may be missing an else clause
--> $DIR/if-without-else-as-fn-expr.rs:10:20
--> $DIR/if-without-else-as-fn-expr.rs:9:20
|
LL | let x: usize = if bar % 5 == 0 {
| _________-__________^
Expand All @@ -52,19 +29,8 @@ LL | | };
= note: `if` expressions without `else` evaluate to `()`
= help: consider adding an `else` block that evaluates to the expected type

error[E0308]: mismatched types
--> $DIR/if-without-else-as-fn-expr.rs:19:5
|
LL | / if bar % 5 == 0 {
LL | | 3
LL | | }
| |_____^ expected usize, found ()
|
= note: expected type `usize`
found type `()`

error[E0317]: if may be missing an else clause
--> $DIR/if-without-else-as-fn-expr.rs:19:5
--> $DIR/if-without-else-as-fn-expr.rs:17:5
|
LL | fn foo3(bar: usize) -> usize {
| ----- expected `usize` because of this return type
Expand All @@ -78,19 +44,8 @@ LL | | }
= note: `if` expressions without `else` evaluate to `()`
= help: consider adding an `else` block that evaluates to the expected type

error[E0308]: mismatched types
--> $DIR/if-without-else-as-fn-expr.rs:27:5
|
LL | / if let 0 = 1 {
LL | | return 3;
LL | | }
| |_____^ expected usize, found ()
|
= note: expected type `usize`
found type `()`

error[E0317]: if may be missing an else clause
--> $DIR/if-without-else-as-fn-expr.rs:27:5
--> $DIR/if-without-else-as-fn-expr.rs:24:5
|
LL | fn foo_let(bar: usize) -> usize {
| ----- expected `usize` because of this return type
Expand All @@ -104,20 +59,8 @@ LL | | }
= note: `if` expressions without `else` evaluate to `()`
= help: consider adding an `else` block that evaluates to the expected type

error[E0308]: mismatched types
--> $DIR/if-without-else-as-fn-expr.rs:35:20
|
LL | let x: usize = if let 0 = 1 {
| ____________________^
LL | | return 3;
LL | | };
| |_____^ expected usize, found ()
|
= note: expected type `usize`
found type `()`

error[E0317]: if may be missing an else clause
--> $DIR/if-without-else-as-fn-expr.rs:35:20
--> $DIR/if-without-else-as-fn-expr.rs:31:20
|
LL | let x: usize = if let 0 = 1 {
| _________-__________^
Expand All @@ -132,19 +75,8 @@ LL | | };
= note: `if` expressions without `else` evaluate to `()`
= help: consider adding an `else` block that evaluates to the expected type

error[E0308]: mismatched types
--> $DIR/if-without-else-as-fn-expr.rs:44:5
|
LL | / if let 0 = 1 {
LL | | 3
LL | | }
| |_____^ expected usize, found ()
|
= note: expected type `usize`
found type `()`

error[E0317]: if may be missing an else clause
--> $DIR/if-without-else-as-fn-expr.rs:44:5
--> $DIR/if-without-else-as-fn-expr.rs:39:5
|
LL | fn foo3_let(bar: usize) -> usize {
| ----- expected `usize` because of this return type
Expand All @@ -158,7 +90,6 @@ LL | | }
= note: `if` expressions without `else` evaluate to `()`
= help: consider adding an `else` block that evaluates to the expected type

error: aborting due to 12 previous errors
error: aborting due to 6 previous errors

Some errors have detailed explanations: E0308, E0317.
For more information about an error, try `rustc --explain E0308`.
For more information about this error, try `rustc --explain E0317`.
1 change: 0 additions & 1 deletion src/test/ui/issues/issue-50577.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,5 @@ fn main() {
enum Foo {
Drop = assert_eq!(1, 1)
//~^ ERROR if may be missing an else clause
//~| ERROR mismatched types [E0308]
}
}
15 changes: 2 additions & 13 deletions src/test/ui/issues/issue-50577.stderr
View file
Original file line number Diff line number Diff line change
@@ -1,13 +1,3 @@
error[E0308]: mismatched types
--> $DIR/issue-50577.rs:3:16
|
LL | Drop = assert_eq!(1, 1)
| ^^^^^^^^^^^^^^^^ expected isize, found ()
|
= note: expected type `isize`
found type `()`
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error[E0317]: if may be missing an else clause
--> $DIR/issue-50577.rs:3:16
|
Expand All @@ -23,7 +13,6 @@ LL | Drop = assert_eq!(1, 1)
= help: consider adding an `else` block that evaluates to the expected type
= note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)

error: aborting due to 2 previous errors
error: aborting due to previous error

Some errors have detailed explanations: E0308, E0317.
For more information about an error, try `rustc --explain E0308`.
For more information about this error, try `rustc --explain E0317`.

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