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Rollup merge of rust-lang#82364 - osa1:issue82361, r=estebank
Improve error msgs when found type is deref of expected This improves help messages in two cases: - When expected type is `T` and found type is `&T`, we now look through blocks and suggest dereferencing the expression of the block, rather than the whole block. - In the above case, if the expression is an `&`, we not suggest removing the `&` instead of adding `*`. Both of these are demonstrated in the regression test. Before this patch the first error in the test would be: error[E0308]: `if` and `else` have incompatible types --> test.rs:8:9 | 5 | / if true { 6 | | a | | - expected because of this 7 | | } else { 8 | | b | | ^ expected `usize`, found `&usize` 9 | | }; | |_____- `if` and `else` have incompatible types | help: consider dereferencing the borrow | 7 | } else *{ 8 | b 9 | }; | Now: error[E0308]: `if` and `else` have incompatible types --> test.rs:8:9 | 5 | / if true { 6 | | a | | - expected because of this 7 | | } else { 8 | | b | | ^ | | | | | expected `usize`, found `&usize` | | help: consider dereferencing the borrow: `*b` 9 | | }; | |_____- `if` and `else` have incompatible types The second error: error[E0308]: `if` and `else` have incompatible types --> test.rs:14:9 | 11 | / if true { 12 | | 1 | | - expected because of this 13 | | } else { 14 | | &1 | | ^^ expected integer, found `&{integer}` 15 | | }; | |_____- `if` and `else` have incompatible types | help: consider dereferencing the borrow | 13 | } else *{ 14 | &1 15 | }; | now: error[E0308]: `if` and `else` have incompatible types --> test.rs:14:9 | 11 | / if true { 12 | | 1 | | - expected because of this 13 | | } else { 14 | | &1 | | ^- | | || | | |help: consider removing the `&`: `1` | | expected integer, found `&{integer}` 15 | | }; | |_____- `if` and `else` have incompatible types Fixes rust-lang#82361 --- r? ````@estebank````
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‎compiler/rustc_hir/src/hir.rs

+8
Original file line numberDiff line numberDiff line change
@@ -1577,6 +1577,14 @@ impl Expr<'_> {
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expr
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}
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pub fn peel_blocks(&self) -> &Self {
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let mut expr = self;
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while let ExprKind::Block(Block { expr: Some(inner), .. }, _) = &expr.kind {
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expr = inner;
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}
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expr
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}
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pub fn can_have_side_effects(&self) -> bool {
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match self.peel_drop_temps().kind {
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ExprKind::Path(_) | ExprKind::Lit(_) => false,

‎compiler/rustc_typeck/src/check/demand.rs

+24-4
Original file line numberDiff line numberDiff line change
@@ -616,10 +616,30 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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}
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_ if sp == expr.span && !is_macro => {
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if let Some(steps) = self.deref_steps(checked_ty, expected) {
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let expr = expr.peel_blocks();
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619621
if steps == 1 {
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// For a suggestion to make sense, the type would need to be `Copy`.
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if self.infcx.type_is_copy_modulo_regions(self.param_env, expected, sp) {
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if let Ok(code) = sm.span_to_snippet(sp) {
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if let hir::ExprKind::AddrOf(_, mutbl, inner) = expr.kind {
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// If the expression has `&`, removing it would fix the error
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let prefix_span = expr.span.with_hi(inner.span.lo());
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let message = match mutbl {
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hir::Mutability::Not => "consider removing the `&`",
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hir::Mutability::Mut => "consider removing the `&mut`",
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};
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let suggestion = String::new();
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return Some((
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prefix_span,
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message,
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suggestion,
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Applicability::MachineApplicable,
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));
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} else if self.infcx.type_is_copy_modulo_regions(
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self.param_env,
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expected,
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sp,
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) {
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// For this suggestion to make sense, the type would need to be `Copy`.
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if let Ok(code) = sm.span_to_snippet(expr.span) {
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let message = if checked_ty.is_region_ptr() {
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"consider dereferencing the borrow"
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} else {
@@ -631,7 +651,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
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format!("*{}", code)
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};
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return Some((
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sp,
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expr.span,
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message,
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suggestion,
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Applicability::MachineApplicable,

‎src/test/ui/suggestions/issue-82361.fixed

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,24 @@
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// run-rustfix
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fn main() {
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let a: usize = 123;
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let b: &usize = &a;
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if true {
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a
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} else {
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*b //~ ERROR `if` and `else` have incompatible types [E0308]
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};
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if true {
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1
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} else {
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1 //~ ERROR `if` and `else` have incompatible types [E0308]
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};
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if true {
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1
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} else {
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1 //~ ERROR `if` and `else` have incompatible types [E0308]
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};
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}

‎src/test/ui/suggestions/issue-82361.rs

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,24 @@
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// run-rustfix
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fn main() {
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let a: usize = 123;
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let b: &usize = &a;
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if true {
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a
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} else {
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b //~ ERROR `if` and `else` have incompatible types [E0308]
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};
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if true {
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1
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} else {
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&1 //~ ERROR `if` and `else` have incompatible types [E0308]
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};
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if true {
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1
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} else {
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&mut 1 //~ ERROR `if` and `else` have incompatible types [E0308]
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};
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}

‎src/test/ui/suggestions/issue-82361.stderr

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,48 @@
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error[E0308]: `if` and `else` have incompatible types
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--> $DIR/issue-82361.rs:10:9
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|
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LL | / if true {
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LL | | a
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| | - expected because of this
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LL | | } else {
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LL | | b
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| | ^
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| | |
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| | expected `usize`, found `&usize`
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| | help: consider dereferencing the borrow: `*b`
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LL | | };
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| |_____- `if` and `else` have incompatible types
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error[E0308]: `if` and `else` have incompatible types
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--> $DIR/issue-82361.rs:16:9
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|
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LL | / if true {
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LL | | 1
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| | - expected because of this
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LL | | } else {
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LL | | &1
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| | -^
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| | |
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| | expected integer, found `&{integer}`
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| | help: consider removing the `&`
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LL | | };
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| |_____- `if` and `else` have incompatible types
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error[E0308]: `if` and `else` have incompatible types
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--> $DIR/issue-82361.rs:22:9
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|
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LL | / if true {
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LL | | 1
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| | - expected because of this
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LL | | } else {
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LL | | &mut 1
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| | -----^
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| | |
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| | expected integer, found `&mut {integer}`
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| | help: consider removing the `&mut`
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LL | | };
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| |_____- `if` and `else` have incompatible types
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error: aborting due to 3 previous errors
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For more information about this error, try `rustc --explain E0308`.

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