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Detect bindings assigned blocks without tail expressions

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Address  #44173 for type check errors.
This commit is contained in:
Esteban Küber 2023-01-06 00:45:10 +00:00
parent 388538fc96
commit 1983a627b3
3 changed files with 140 additions and 0 deletions
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45
compiler/rustc_hir_typeck/src/demand.rs
View file

@ -75,6 +75,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
self.note_need_for_fn_pointer(err, expected, expr_ty);
self.note_internal_mutation_in_method(err, expr, expected, expr_ty);
self.check_for_range_as_method_call(err, expr, expr_ty, expected);
self.check_for_binding_assigned_block_without_tail_expression(err, expr, expr_ty, expected);
}
/// Requires that the two types unify, and prints an error message if
@ -1670,4 +1671,48 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
Applicability::MachineApplicable,
);
}
/// Identify when the type error is because `()` is found in a binding that was assigned a
/// block without a tail expression.
fn check_for_binding_assigned_block_without_tail_expression(
&self,
err: &mut Diagnostic,
expr: &hir::Expr<'_>,
checked_ty: Ty<'tcx>,
expected_ty: Ty<'tcx>,
) {
if !checked_ty.is_unit() {
return;
}
let hir::ExprKind::Path(hir::QPath::Resolved(None, path)) = expr.kind else { return; };
let hir::def::Res::Local(hir_id) = path.res else { return; };
let Some(hir::Node::Pat(pat)) = self.tcx.hir().find(hir_id) else {
return;
};
let Some(hir::Node::Local(hir::Local {
ty: None,
init: Some(init),
..
})) = self.tcx.hir().find_parent(pat.hir_id) else { return; };
let hir::ExprKind::Block(block, None) = init.kind else { return; };
if block.expr.is_some() {
return;
}
let [.., stmt] = block.stmts else {
err.span_help(block.span, "this empty block is missing a tail expression");
return;
};
let hir::StmtKind::Semi(tail_expr) = stmt.kind else { return; };
let Some(ty) = self.node_ty_opt(tail_expr.hir_id) else { return; };
if self.can_eq(self.param_env, expected_ty, ty).is_ok() {
err.span_suggestion_verbose(
stmt.span.with_lo(tail_expr.span.hi()),
"remove this semicolon",
"",
Applicability::MachineApplicable,
);
} else {
err.span_help(block.span, "this block is missing a tail expression");
}
}
}

16
src/test/ui/type/binding-assigned-block-without-tail-expression.rs Normal file
View file

@ -0,0 +1,16 @@
fn main() {
let x = {
println!("foo");
42;
};
let y = {};
let z = {
"hi";
};
println!("{}", x); //~ ERROR E0277
println!("{}", y); //~ ERROR E0277
println!("{}", z); //~ ERROR E0277
let _: i32 = x; //~ ERROR E0308
let _: i32 = y; //~ ERROR E0308
let _: i32 = z; //~ ERROR E0308
}

79
src/test/ui/type/binding-assigned-block-without-tail-expression.stderr Normal file
View file

@ -0,0 +1,79 @@
error[E0277]: `()` doesn't implement `std::fmt::Display`
--> $DIR/binding-assigned-block-without-tail-expression.rs:10:20
|
LL | println!("{}", x);
| ^ `()` cannot be formatted with the default formatter
|
= help: the trait `std::fmt::Display` is not implemented for `()`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
error[E0277]: `()` doesn't implement `std::fmt::Display`
--> $DIR/binding-assigned-block-without-tail-expression.rs:11:20
|
LL | println!("{}", y);
| ^ `()` cannot be formatted with the default formatter
|
= help: the trait `std::fmt::Display` is not implemented for `()`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
error[E0277]: `()` doesn't implement `std::fmt::Display`
--> $DIR/binding-assigned-block-without-tail-expression.rs:12:20
|
LL | println!("{}", z);
| ^ `()` cannot be formatted with the default formatter
|
= help: the trait `std::fmt::Display` is not implemented for `()`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
= note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
error[E0308]: mismatched types
--> $DIR/binding-assigned-block-without-tail-expression.rs:13:18
|
LL | let _: i32 = x;
| --- ^ expected `i32`, found `()`
| |
| expected due to this
|
help: remove this semicolon
|
LL - 42;
LL + 42
|
error[E0308]: mismatched types
--> $DIR/binding-assigned-block-without-tail-expression.rs:14:18
|
LL | let _: i32 = y;
| --- ^ expected `i32`, found `()`
| |
| expected due to this
|
help: this empty block is missing a tail expression
--> $DIR/binding-assigned-block-without-tail-expression.rs:6:13
|
LL | let y = {};
| ^^
error[E0308]: mismatched types
--> $DIR/binding-assigned-block-without-tail-expression.rs:15:18
|
LL | let _: i32 = z;
| --- ^ expected `i32`, found `()`
| |
| expected due to this
|
help: this block is missing a tail expression
--> $DIR/binding-assigned-block-without-tail-expression.rs:7:13
|
LL | let z = {
| _____________^
LL | | "hi";
LL | | };
| |_____^
error: aborting due to 6 previous errors
Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.