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Auto merge of #57381 - estebank:if-else-308, r=nikomatsakis

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Tweak output of type mismatch between "then" and `else` `if` arms

```
error[E0308]: if and else have incompatible types
  --> $DIR/if-else-type-mismatch.rs:5:9
   |
LL |       let _ = if true {
   |  _____________-
LL | |         42i32
   | |         ----- expected because of this
LL | |     } else {
LL | |         42u32
   | |         ^^^^^ expected i32, found u32
LL | |     };
   | |_____- if and else have incompatible types
   |
   = note: expected type `i32`
              found type `u32`

error[E0308]: if and else have incompatible types
  --> file.rs:2:38
   |
LL |     let _ = if false { 3u8; } else { 3u8 };
   |                        ----          ^^^ expected (), found u8
   |                        |  |
   |                        |  help: consider removing this semicolon
   |                        expected because of this
   |
   = note: expected type `()`
              found type `u8`

error[E0308]: if and else have incompatible types
  --> file.rs:3:37
   |
LL |     let _ = if false { 3u8 } else { 3u8; };
   |                        ---          ^^^-
   |                        |            |  |
   |                        |            |  help: consider removing this semicolon
   |                        |            expected u8, found ()
   |                        expected because of this
   |
   = note: expected type `u8`
              found type `()`

error[E0308]: if and else have incompatible types
  --> file.rs:4:37
   |
LL |     let _ = if false { 3i8 } else { 3u8 };
   |                        ---          ^^^ expected i8, found u8
   |                        |
   |                        expected because of this
   |
   = note: expected type `i8`
              found type `u8`
```

Fix #57348.
This commit is contained in:
bors 2019-01-14 03:49:25 +00:00
commit 0bc0015f20
10 changed files with 331 additions and 28 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

16
src/librustc/infer/error_reporting/mod.rs
View File

@ -511,6 +511,18 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
}
}
},
ObligationCauseCode::IfExpression { then, outer, semicolon } => {
err.span_label(then, "expected because of this");
outer.map(|sp| err.span_label(sp, "if and else have incompatible types"));
if let Some(sp) = semicolon {
err.span_suggestion_short_with_applicability(
sp,
"consider removing this semicolon",
String::new(),
Applicability::MachineApplicable,
);
}
}
_ => (),
}
}
@ -1460,7 +1472,7 @@ impl<'tcx> ObligationCause<'tcx> {
}
_ => "match arms have incompatible types",
}),
IfExpression => Error0308("if and else have incompatible types"),
IfExpression { .. } => Error0308("if and else have incompatible types"),
IfExpressionWithNoElse => Error0317("if may be missing an else clause"),
MainFunctionType => Error0580("main function has wrong type"),
StartFunctionType => Error0308("start function has wrong type"),
@ -1488,7 +1500,7 @@ impl<'tcx> ObligationCause<'tcx> {
hir::MatchSource::IfLetDesugar { .. } => "`if let` arms have compatible types",
_ => "match arms have compatible types",
},
IfExpression => "if and else have compatible types",
IfExpression { .. } => "if and else have compatible types",
IfExpressionWithNoElse => "if missing an else returns ()",
MainFunctionType => "`main` function has the correct type",
StartFunctionType => "`start` function has the correct type",

2
src/librustc/traits/error_reporting.rs
View File

@ -1445,7 +1445,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
ObligationCauseCode::ExprAssignable |
ObligationCauseCode::MatchExpressionArm { .. } |
ObligationCauseCode::MatchExpressionArmPattern { .. } |
ObligationCauseCode::IfExpression |
ObligationCauseCode::IfExpression { .. } |
ObligationCauseCode::IfExpressionWithNoElse |
ObligationCauseCode::MainFunctionType |
ObligationCauseCode::StartFunctionType |

6
src/librustc/traits/mod.rs
View File

@ -229,7 +229,11 @@ pub enum ObligationCauseCode<'tcx> {
MatchExpressionArmPattern { span: Span, ty: Ty<'tcx> },
/// Computing common supertype in an if expression
IfExpression,
IfExpression {
then: Span,
outer: Option<Span>,
semicolon: Option<Span>,
},
/// Computing common supertype of an if expression with no else counter-part
IfExpressionWithNoElse,

6
src/librustc/traits/structural_impls.rs
View File

@ -520,7 +520,11 @@ impl<'a, 'tcx> Lift<'tcx> for traits::ObligationCauseCode<'a> {
super::MatchExpressionArmPattern { span, ty } => {
tcx.lift(&ty).map(|ty| super::MatchExpressionArmPattern { span, ty })
}
super::IfExpression => Some(super::IfExpression),
super::IfExpression { then, outer, semicolon } => Some(super::IfExpression {
then,
outer,
semicolon,
}),
super::IfExpressionWithNoElse => Some(super::IfExpressionWithNoElse),
super::MainFunctionType => Some(super::MainFunctionType),
super::StartFunctionType => Some(super::StartFunctionType),

133
src/librustc_typeck/check/mod.rs
View File

@ -3366,13 +3366,103 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
let coerce_to_ty = expected.coercion_target_type(self, sp);
let mut coerce: DynamicCoerceMany = CoerceMany::new(coerce_to_ty);
let if_cause = self.cause(sp, ObligationCauseCode::IfExpression);
coerce.coerce(self, &if_cause, then_expr, then_ty);
coerce.coerce(self, &self.misc(sp), then_expr, then_ty);
if let Some(else_expr) = opt_else_expr {
let else_ty = self.check_expr_with_expectation(else_expr, expected);
let else_diverges = self.diverges.get();
let mut outer_sp = if self.tcx.sess.source_map().is_multiline(sp) {
// The `if`/`else` isn't in one line in the output, include some context to make it
// clear it is an if/else expression:
// ```
// LL | let x = if true {
// | _____________-
// LL || 10i32
// || ----- expected because of this
// LL || } else {
// LL || 10u32
// || ^^^^^ expected i32, found u32
// LL || };
// ||_____- if and else have incompatible types
// ```
Some(sp)
} else {
// The entire expression is in one line, only point at the arms
// ```
// LL | let x = if true { 10i32 } else { 10u32 };
// | ----- ^^^^^ expected i32, found u32
// | |
// | expected because of this
// ```
None
};
let mut remove_semicolon = None;
let error_sp = if let ExprKind::Block(block, _) = &else_expr.node {
if let Some(expr) = &block.expr {
expr.span
} else if let Some(stmt) = block.stmts.last() {
// possibly incorrect trailing `;` in the else arm
remove_semicolon = self.could_remove_semicolon(block, then_ty);
stmt.span
} else { // empty block, point at its entirety
// Avoid overlapping spans that aren't as readable:
// ```
// 2 | let x = if true {
// | _____________-
// 3 | | 3
// | | - expected because of this
// 4 | | } else {
// | |____________^
// 5 | ||
// 6 | || };
// | || ^
// | ||_____|
// | |______if and else have incompatible types
// | expected integer, found ()
// ```
// by not pointing at the entire expression:
// ```
// 2 | let x = if true {
// | ------- if and else have incompatible types
// 3 | 3
// | - expected because of this
// 4 | } else {
// | ____________^
// 5 | |
// 6 | | };
// | |_____^ expected integer, found ()
// ```
if outer_sp.is_some() {
outer_sp = Some(self.tcx.sess.source_map().def_span(sp));
}
else_expr.span
}
} else { // shouldn't happen unless the parser has done something weird
else_expr.span
};
let then_sp = if let ExprKind::Block(block, _) = &then_expr.node {
if let Some(expr) = &block.expr {
expr.span
} else if let Some(stmt) = block.stmts.last() {
// possibly incorrect trailing `;` in the else arm
remove_semicolon = remove_semicolon.or(
self.could_remove_semicolon(block, else_ty));
stmt.span
} else { // empty block, point at its entirety
outer_sp = None; // same as in `error_sp`, cleanup output
then_expr.span
}
} else { // shouldn't happen unless the parser has done something weird
then_expr.span
};
let if_cause = self.cause(error_sp, ObligationCauseCode::IfExpression {
then: then_sp,
outer: outer_sp,
semicolon: remove_semicolon,
});
coerce.coerce(self, &if_cause, else_expr, else_ty);
// We won't diverge unless both branches do (or the condition does).
@ -5144,7 +5234,6 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
}
}
/// A common error is to add an extra semicolon:
///
/// ```
@ -5156,31 +5245,43 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
/// This routine checks if the final statement in a block is an
/// expression with an explicit semicolon whose type is compatible
/// with `expected_ty`. If so, it suggests removing the semicolon.
fn consider_hint_about_removing_semicolon(&self,
blk: &'gcx hir::Block,
expected_ty: Ty<'tcx>,
err: &mut DiagnosticBuilder) {
fn consider_hint_about_removing_semicolon(
&self,
blk: &'gcx hir::Block,
expected_ty: Ty<'tcx>,
err: &mut DiagnosticBuilder,
) {
if let Some(span_semi) = self.could_remove_semicolon(blk, expected_ty) {
err.span_suggestion_with_applicability(
span_semi,
"consider removing this semicolon",
String::new(),
Applicability::MachineApplicable,
);
}
}
fn could_remove_semicolon(
&self,
blk: &'gcx hir::Block,
expected_ty: Ty<'tcx>,
) -> Option<Span> {
// Be helpful when the user wrote `{... expr;}` and
// taking the `;` off is enough to fix the error.
let last_stmt = match blk.stmts.last() {
Some(s) => s,
None => return,
None => return None,
};
let last_expr = match last_stmt.node {
hir::StmtKind::Semi(ref e, _) => e,
_ => return,
_ => return None,
};
let last_expr_ty = self.node_ty(last_expr.hir_id);
if self.can_sub(self.param_env, last_expr_ty, expected_ty).is_err() {
return;
return None;
}
let original_span = original_sp(last_stmt.span, blk.span);
let span_semi = original_span.with_lo(original_span.hi() - BytePos(1));
err.span_suggestion_with_applicability(
span_semi,
"consider removing this semicolon",
String::new(),
Applicability::MachineApplicable);
Some(original_span.with_lo(original_span.hi() - BytePos(1)))
}
// Instantiates the given path, which must refer to an item with the given

46
src/test/ui/if-else-type-mismatch.rs Normal file
View File

@ -0,0 +1,46 @@
fn main() {
let _ = if true {
1i32
} else {
2u32
};
//~^^ ERROR if and else have incompatible types
let _ = if true { 42i32 } else { 42u32 };
//~^ ERROR if and else have incompatible types
let _ = if true {
3u32;
} else {
4u32
};
//~^^ ERROR if and else have incompatible types
let _ = if true {
5u32
} else {
6u32;
};
//~^^ ERROR if and else have incompatible types
let _ = if true {
7i32;
} else {
8u32
};
//~^^ ERROR if and else have incompatible types
let _ = if true {
9i32
} else {
10u32;
};
//~^^ ERROR if and else have incompatible types
let _ = if true {
} else {
11u32
};
//~^^ ERROR if and else have incompatible types
let _ = if true {
12i32
} else {
};
//~^^^ ERROR if and else have incompatible types
}

130
src/test/ui/if-else-type-mismatch.stderr Normal file
View File

@ -0,0 +1,130 @@
error[E0308]: if and else have incompatible types
--> $DIR/if-else-type-mismatch.rs:5:9
|
LL | let _ = if true {
| _____________-
LL | | 1i32
| | ---- expected because of this
LL | | } else {
LL | | 2u32
| | ^^^^ expected i32, found u32
LL | | };
| |_____- if and else have incompatible types
|
= note: expected type `i32`
found type `u32`
error[E0308]: if and else have incompatible types
--> $DIR/if-else-type-mismatch.rs:8:38
|
LL | let _ = if true { 42i32 } else { 42u32 };
| ----- ^^^^^ expected i32, found u32
| |
| expected because of this
|
= note: expected type `i32`
found type `u32`
error[E0308]: if and else have incompatible types
--> $DIR/if-else-type-mismatch.rs:13:9
|
LL | let _ = if true {
| _____________-
LL | | 3u32;
| | -----
| | | |
| | | help: consider removing this semicolon
| | expected because of this
LL | | } else {
LL | | 4u32
| | ^^^^ expected (), found u32
LL | | };
| |_____- if and else have incompatible types
|
= note: expected type `()`
found type `u32`
error[E0308]: if and else have incompatible types
--> $DIR/if-else-type-mismatch.rs:19:9
|
LL | let _ = if true {
| _____________-
LL | | 5u32
| | ---- expected because of this
LL | | } else {
LL | | 6u32;
| | ^^^^-
| | | |
| | | help: consider removing this semicolon
| | expected u32, found ()
LL | | };
| |_____- if and else have incompatible types
|
= note: expected type `u32`
found type `()`
error[E0308]: if and else have incompatible types
--> $DIR/if-else-type-mismatch.rs:25:9
|
LL | let _ = if true {
| _____________-
LL | | 7i32;
| | ----- expected because of this
LL | | } else {
LL | | 8u32
| | ^^^^ expected (), found u32
LL | | };
| |_____- if and else have incompatible types
|
= note: expected type `()`
found type `u32`
error[E0308]: if and else have incompatible types
--> $DIR/if-else-type-mismatch.rs:31:9
|
LL | let _ = if true {
| _____________-
LL | | 9i32
| | ---- expected because of this
LL | | } else {
LL | | 10u32;
| | ^^^^^^ expected i32, found ()
LL | | };
| |_____- if and else have incompatible types
|
= note: expected type `i32`
found type `()`
error[E0308]: if and else have incompatible types
--> $DIR/if-else-type-mismatch.rs:37:9
|
LL | let _ = if true {
| _____________________-
LL | |
LL | | } else {
| |_____- expected because of this
LL | 11u32
| ^^^^^ expected (), found u32
|
= note: expected type `()`
found type `u32`
error[E0308]: if and else have incompatible types
--> $DIR/if-else-type-mismatch.rs:42:12
|
LL | let _ = if true {
| ------- if and else have incompatible types
LL | 12i32
| ----- expected because of this
LL | } else {
| ____________^
LL | |
LL | | };
| |_____^ expected i32, found ()
|
= note: expected type `i32`
found type `()`
error: aborting due to 8 previous errors
For more information about this error, try `rustc --explain E0308`.

6
src/test/ui/if/if-branch-types.stderr
View File

@ -1,8 +1,10 @@
error[E0308]: if and else have incompatible types
--> $DIR/if-branch-types.rs:2:13
--> $DIR/if-branch-types.rs:2:38
|
LL | let x = if true { 10i32 } else { 10u32 };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected i32, found u32
| ----- ^^^^^ expected i32, found u32
| |
| expected because of this
|
= note: expected type `i32`
found type `u32`

8
src/test/ui/regions/region-invariant-static-error-reporting.stderr
View File

@ -1,13 +1,15 @@
error[E0308]: if and else have incompatible types
--> $DIR/region-invariant-static-error-reporting.rs:14:15
--> $DIR/region-invariant-static-error-reporting.rs:17:9
|
LL | let bad = if x.is_some() {
| _______________^
| _______________-
LL | | x.unwrap()
| | ---------- expected because of this
LL | | } else {
LL | | mk_static()
| | ^^^^^^^^^^^ lifetime mismatch
LL | | };
| |_____^ lifetime mismatch
| |_____- if and else have incompatible types
|
= note: expected type `Invariant<'a>`
found type `Invariant<'static>`

6
src/test/ui/str/str-array-assignment.stderr
View File

@ -1,8 +1,10 @@
error[E0308]: if and else have incompatible types
--> $DIR/str-array-assignment.rs:3:11
--> $DIR/str-array-assignment.rs:3:37
|
LL | let t = if true { s[..2] } else { s };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected str, found &str
| ------ ^ expected str, found &str
| |
| expected because of this
|
= note: expected type `str`
found type `&str`