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Auto merge of #123125 - gurry:122561-bad-note-non-zero-loop-iters-2, r=estebank

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Remove suggestion about iteration count in coerce

Fixes #122561

The iteration count-centric suggestion was implemented in PR #100094, but it was based on the wrong assumption that the type mismatch error depends on the number of times the loop iterates. As it turns out, that is not true (see this comment for details: https://github.com/rust-lang/rust/pull/122679#issuecomment-2017432531)

This PR attempts to remedy the situation by changing the suggestion from the one centered on iteration count to a simple suggestion to add a return value.

It should also fix #100285 by simply making it redundant.
This commit is contained in:
bors 2024-05-05 12:51:37 +00:00
commit 06e88c306a
13 changed files with 545 additions and 205 deletions
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155
compiler/rustc_hir_typeck/src/coercion.rs
View File

@ -37,11 +37,9 @@
use crate::errors::SuggestBoxingForReturnImplTrait;
use crate::FnCtxt;
use rustc_errors::{codes::*, struct_span_code_err, Applicability, Diag, MultiSpan};
use rustc_errors::{codes::*, struct_span_code_err, Applicability, Diag};
use rustc_hir as hir;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::intravisit::{self, Visitor};
use rustc_hir::Expr;
use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer;
use rustc_infer::infer::type_variable::TypeVariableOrigin;
use rustc_infer::infer::{Coercion, DefineOpaqueTypes, InferOk, InferResult};
@ -93,22 +91,6 @@ impl<'a, 'tcx> Deref for Coerce<'a, 'tcx> {
type CoerceResult<'tcx> = InferResult<'tcx, (Vec<Adjustment<'tcx>>, Ty<'tcx>)>;
struct CollectRetsVisitor<'tcx> {
ret_exprs: Vec<&'tcx hir::Expr<'tcx>>,
}
impl<'tcx> Visitor<'tcx> for CollectRetsVisitor<'tcx> {
fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
match expr.kind {
hir::ExprKind::Ret(_) => self.ret_exprs.push(expr),
// `return` in closures does not return from the outer function
hir::ExprKind::Closure(_) => return,
_ => {}
}
intravisit::walk_expr(self, expr);
}
}
/// Coercing a mutable reference to an immutable works, while
/// coercing `&T` to `&mut T` should be forbidden.
fn coerce_mutbls<'tcx>(
@ -1597,7 +1579,6 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
let mut err;
let mut unsized_return = false;
let mut visitor = CollectRetsVisitor { ret_exprs: vec![] };
match *cause.code() {
ObligationCauseCode::ReturnNoExpression => {
err = struct_span_code_err!(
@ -1632,11 +1613,6 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
if !fcx.tcx.features().unsized_locals {
unsized_return = self.is_return_ty_definitely_unsized(fcx);
}
if let Some(expression) = expression
&& let hir::ExprKind::Loop(loop_blk, ..) = expression.kind
{
intravisit::walk_block(&mut visitor, loop_blk);
}
}
ObligationCauseCode::ReturnValue(id) => {
err = self.report_return_mismatched_types(
@ -1737,6 +1713,22 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
augment_error(&mut err);
if let Some(expr) = expression {
if let hir::ExprKind::Loop(
_,
_,
loop_src @ (hir::LoopSource::While | hir::LoopSource::ForLoop),
_,
) = expr.kind
{
let loop_type = if loop_src == hir::LoopSource::While {
"`while` loops"
} else {
"`for` loops"
};
err.note(format!("{loop_type} evaluate to unit type `()`"));
}
fcx.emit_coerce_suggestions(
&mut err,
expr,
@ -1745,15 +1737,6 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
None,
Some(coercion_error),
);
if visitor.ret_exprs.len() > 0 {
self.note_unreachable_loop_return(
&mut err,
fcx.tcx,
&expr,
&visitor.ret_exprs,
expected,
);
}
}
let reported = err.emit_unless(unsized_return);
@ -1827,110 +1810,6 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
);
}
fn note_unreachable_loop_return(
&self,
err: &mut Diag<'_>,
tcx: TyCtxt<'tcx>,
expr: &hir::Expr<'tcx>,
ret_exprs: &Vec<&'tcx hir::Expr<'tcx>>,
ty: Ty<'tcx>,
) {
let hir::ExprKind::Loop(_, _, _, loop_span) = expr.kind else {
return;
};
let mut span: MultiSpan = vec![loop_span].into();
span.push_span_label(loop_span, "this might have zero elements to iterate on");
const MAXITER: usize = 3;
let iter = ret_exprs.iter().take(MAXITER);
for ret_expr in iter {
span.push_span_label(
ret_expr.span,
"if the loop doesn't execute, this value would never get returned",
);
}
err.span_note(
span,
"the function expects a value to always be returned, but loops might run zero times",
);
if MAXITER < ret_exprs.len() {
err.note(format!(
"if the loop doesn't execute, {} other values would never get returned",
ret_exprs.len() - MAXITER
));
}
let hir = tcx.hir();
let item = hir.get_parent_item(expr.hir_id);
let ret_msg = "return a value for the case when the loop has zero elements to iterate on";
let ret_ty_msg =
"otherwise consider changing the return type to account for that possibility";
let node = tcx.hir_node(item.into());
if let Some(body_id) = node.body_id()
&& let Some(sig) = node.fn_sig()
&& let hir::ExprKind::Block(block, _) = hir.body(body_id).value.kind
&& !ty.is_never()
{
let indentation = if let None = block.expr
&& let [.., last] = &block.stmts
{
tcx.sess.source_map().indentation_before(last.span).unwrap_or_else(String::new)
} else if let Some(expr) = block.expr {
tcx.sess.source_map().indentation_before(expr.span).unwrap_or_else(String::new)
} else {
String::new()
};
if let None = block.expr
&& let [.., last] = &block.stmts
{
err.span_suggestion_verbose(
last.span.shrink_to_hi(),
ret_msg,
format!("\n{indentation}/* `{ty}` value */"),
Applicability::MaybeIncorrect,
);
} else if let Some(expr) = block.expr {
err.span_suggestion_verbose(
expr.span.shrink_to_hi(),
ret_msg,
format!("\n{indentation}/* `{ty}` value */"),
Applicability::MaybeIncorrect,
);
}
let mut sugg = match sig.decl.output {
hir::FnRetTy::DefaultReturn(span) => {
vec![(span, " -> Option<()>".to_string())]
}
hir::FnRetTy::Return(ty) => {
vec![
(ty.span.shrink_to_lo(), "Option<".to_string()),
(ty.span.shrink_to_hi(), ">".to_string()),
]
}
};
for ret_expr in ret_exprs {
match ret_expr.kind {
hir::ExprKind::Ret(Some(expr)) => {
sugg.push((expr.span.shrink_to_lo(), "Some(".to_string()));
sugg.push((expr.span.shrink_to_hi(), ")".to_string()));
}
hir::ExprKind::Ret(None) => {
sugg.push((ret_expr.span.shrink_to_hi(), " Some(())".to_string()));
}
_ => {}
}
}
if let None = block.expr
&& let [.., last] = &block.stmts
{
sugg.push((last.span.shrink_to_hi(), format!("\n{indentation}None")));
} else if let Some(expr) = block.expr {
sugg.push((expr.span.shrink_to_hi(), format!("\n{indentation}None")));
}
err.multipart_suggestion(ret_ty_msg, sugg, Applicability::MaybeIncorrect);
} else {
err.help(format!("{ret_msg}, {ret_ty_msg}"));
}
}
fn report_return_mismatched_types<'a>(
&self,
cause: &ObligationCause<'tcx>,

3
compiler/rustc_hir_typeck/src/demand.rs
View File

@ -57,7 +57,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
|| self.suggest_into(err, expr, expr_ty, expected)
|| self.suggest_floating_point_literal(err, expr, expected)
|| self.suggest_null_ptr_for_literal_zero_given_to_ptr_arg(err, expr, expected)
|| self.suggest_coercing_result_via_try_operator(err, expr, expected, expr_ty);
|| self.suggest_coercing_result_via_try_operator(err, expr, expected, expr_ty)
|| self.suggest_returning_value_after_loop(err, expr, expected);
if !suggested {
self.note_source_of_type_mismatch_constraint(

89
compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
View File

@ -18,8 +18,8 @@ use rustc_hir::def::Res;
use rustc_hir::def::{CtorKind, CtorOf, DefKind};
use rustc_hir::lang_items::LangItem;
use rustc_hir::{
CoroutineDesugaring, CoroutineKind, CoroutineSource, Expr, ExprKind, GenericBound, HirId, Node,
Path, QPath, Stmt, StmtKind, TyKind, WherePredicate,
Arm, CoroutineDesugaring, CoroutineKind, CoroutineSource, Expr, ExprKind, GenericBound, HirId,
Node, Path, QPath, Stmt, StmtKind, TyKind, WherePredicate,
};
use rustc_hir_analysis::collect::suggest_impl_trait;
use rustc_hir_analysis::hir_ty_lowering::HirTyLowerer;
@ -1942,6 +1942,91 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
false
}
// If the expr is a while or for loop and is the tail expr of its
// enclosing body suggest returning a value right after it
pub fn suggest_returning_value_after_loop(
&self,
err: &mut Diag<'_>,
expr: &hir::Expr<'tcx>,
expected: Ty<'tcx>,
) -> bool {
let hir = self.tcx.hir();
let enclosing_scope =
hir.get_enclosing_scope(expr.hir_id).map(|hir_id| self.tcx.hir_node(hir_id));
// Get tail expr of the enclosing block or body
let tail_expr = if let Some(Node::Block(hir::Block { expr, .. })) = enclosing_scope
&& expr.is_some()
{
*expr
} else {
let body_def_id = hir.enclosing_body_owner(expr.hir_id);
let body_id = hir.body_owned_by(body_def_id);
let body = hir.body(body_id);
// Get tail expr of the body
match body.value.kind {
// Regular function body etc.
hir::ExprKind::Block(block, _) => block.expr,
// Anon const body (there's no block in this case)
hir::ExprKind::DropTemps(expr) => Some(expr),
_ => None,
}
};
let Some(tail_expr) = tail_expr else {
return false; // Body doesn't have a tail expr we can compare with
};
// Get the loop expr within the tail expr
let loop_expr_in_tail = match expr.kind {
hir::ExprKind::Loop(_, _, hir::LoopSource::While, _) => tail_expr,
hir::ExprKind::Loop(_, _, hir::LoopSource::ForLoop, _) => {
match tail_expr.peel_drop_temps() {
Expr { kind: ExprKind::Match(_, [Arm { body, .. }], _), .. } => body,
_ => return false, // Not really a for loop
}
}
_ => return false, // Not a while or a for loop
};
// If the expr is the loop expr in the tail
// then make the suggestion
if expr.hir_id == loop_expr_in_tail.hir_id {
let span = expr.span;
let (msg, suggestion) = if expected.is_never() {
(
"consider adding a diverging expression here",
"`loop {}` or `panic!(\"...\")`".to_string(),
)
} else {
("consider returning a value here", format!("`{expected}` value"))
};
let src_map = self.tcx.sess.source_map();
let suggestion = if src_map.is_multiline(expr.span) {
let indentation = src_map.indentation_before(span).unwrap_or_else(String::new);
format!("\n{indentation}/* {suggestion} */")
} else {
// If the entire expr is on a single line
// put the suggestion also on the same line
format!(" /* {suggestion} */")
};
err.span_suggestion_verbose(
span.shrink_to_hi(),
msg,
suggestion,
Applicability::MaybeIncorrect,
);
true
} else {
false
}
}
/// If the expected type is an enum (Issue #55250) with any variants whose
/// sole field is of the found type, suggest such variants. (Issue #42764)
pub(crate) fn suggest_compatible_variants(

110
tests/ui/coercion/coerce-loop-issue-122561.rs Normal file
View File

@ -0,0 +1,110 @@
// Regression test for #122561
fn for_infinite() -> bool {
for i in 0.. {
//~^ ERROR mismatched types
return false;
}
}
fn for_finite() -> String {
for i in 0..5 {
//~^ ERROR mismatched types
return String::from("test");
}
}
fn for_zero_times() -> bool {
for i in 0..0 {
//~^ ERROR mismatched types
return true;
}
}
fn for_never_type() -> ! {
for i in 0..5 {
//~^ ERROR mismatched types
}
}
// Entire function on a single line.
// Tests that we format the suggestion
// correctly in this case
fn for_single_line() -> bool { for i in 0.. { return false; } }
//~^ ERROR mismatched types
// Loop in an anon const in function args
// Tests that we:
// a. deal properly with this complex case
// b. format the suggestion correctly so
// that it's readable
fn for_in_arg(a: &[(); for x in 0..2 {}]) -> bool {
//~^ ERROR `for` is not allowed in a `const`
//~| ERROR mismatched types
true
}
fn while_inifinite() -> bool {
while true {
//~^ ERROR mismatched types
//~| WARN denote infinite loops with `loop { ... }` [while_true]
return true;
}
}
fn while_finite() -> bool {
let mut i = 0;
while i < 3 {
//~^ ERROR mismatched types
i += 1;
return true;
}
}
fn while_zero_times() -> bool {
while false {
//~^ ERROR mismatched types
return true;
}
}
fn while_never_type() -> ! {
while true {
//~^ ERROR mismatched types
//~| WARN denote infinite loops with `loop { ... }` [while_true]
}
}
// No type mismatch error in this case
fn loop_() -> bool {
loop {
return true;
}
}
const C: i32 = {
for i in 0.. {
//~^ ERROR `for` is not allowed in a `const`
//~| ERROR mismatched types
}
};
fn main() {
let _ = [10; {
for i in 0..5 {
//~^ ERROR `for` is not allowed in a `const`
//~| ERROR mismatched types
}
}];
let _ = [10; {
while false {
//~^ ERROR mismatched types
}
}];
let _ = |a: &[(); for x in 0..2 {}]| {};
//~^ ERROR `for` is not allowed in a `const`
//~| ERROR mismatched types
}

299
tests/ui/coercion/coerce-loop-issue-122561.stderr Normal file
View File

@ -0,0 +1,299 @@
warning: denote infinite loops with `loop { ... }`
--> $DIR/coerce-loop-issue-122561.rs:48:5
|
LL | while true {
| ^^^^^^^^^^ help: use `loop`
|
= note: `#[warn(while_true)]` on by default
warning: denote infinite loops with `loop { ... }`
--> $DIR/coerce-loop-issue-122561.rs:72:5
|
LL | while true {
| ^^^^^^^^^^ help: use `loop`
error[E0658]: `for` is not allowed in a `const`
--> $DIR/coerce-loop-issue-122561.rs:41:24
|
LL | fn for_in_arg(a: &[(); for x in 0..2 {}]) -> bool {
| ^^^^^^^^^^^^^^^^
|
= note: see issue #87575 <https://github.com/rust-lang/rust/issues/87575> for more information
= help: add `#![feature(const_for)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error[E0658]: `for` is not allowed in a `const`
--> $DIR/coerce-loop-issue-122561.rs:86:5
|
LL | / for i in 0.. {
LL | |
LL | |
LL | | }
| |_____^
|
= note: see issue #87575 <https://github.com/rust-lang/rust/issues/87575> for more information
= help: add `#![feature(const_for)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error[E0658]: `for` is not allowed in a `const`
--> $DIR/coerce-loop-issue-122561.rs:94:9
|
LL | / for i in 0..5 {
LL | |
LL | |
LL | | }
| |_________^
|
= note: see issue #87575 <https://github.com/rust-lang/rust/issues/87575> for more information
= help: add `#![feature(const_for)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error[E0658]: `for` is not allowed in a `const`
--> $DIR/coerce-loop-issue-122561.rs:107:23
|
LL | let _ = |a: &[(); for x in 0..2 {}]| {};
| ^^^^^^^^^^^^^^^^
|
= note: see issue #87575 <https://github.com/rust-lang/rust/issues/87575> for more information
= help: add `#![feature(const_for)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:41:24
|
LL | fn for_in_arg(a: &[(); for x in 0..2 {}]) -> bool {
| ^^^^^^^^^^^^^^^^ expected `usize`, found `()`
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL | fn for_in_arg(a: &[(); for x in 0..2 {} /* `usize` value */]) -> bool {
| +++++++++++++++++++
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:86:5
|
LL | / for i in 0.. {
LL | |
LL | |
LL | | }
| |_____^ expected `i32`, found `()`
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `i32` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:4:5
|
LL | fn for_infinite() -> bool {
| ---- expected `bool` because of return type
LL | / for i in 0.. {
LL | |
LL | | return false;
LL | | }
| |_____^ expected `bool`, found `()`
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `bool` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:11:5
|
LL | fn for_finite() -> String {
| ------ expected `String` because of return type
LL | / for i in 0..5 {
LL | |
LL | | return String::from("test");
LL | | }
| |_____^ expected `String`, found `()`
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `String` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:18:5
|
LL | fn for_zero_times() -> bool {
| ---- expected `bool` because of return type
LL | / for i in 0..0 {
LL | |
LL | | return true;
LL | | }
| |_____^ expected `bool`, found `()`
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `bool` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:25:5
|
LL | fn for_never_type() -> ! {
| - expected `!` because of return type
LL | / for i in 0..5 {
LL | |
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
= note: `for` loops evaluate to unit type `()`
help: consider adding a diverging expression here
|
LL ~ }
LL + /* `loop {}` or `panic!("...")` */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:33:32
|
LL | fn for_single_line() -> bool { for i in 0.. { return false; } }
| ---- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `bool`, found `()`
| |
| expected `bool` because of return type
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL | fn for_single_line() -> bool { for i in 0.. { return false; } /* `bool` value */ }
| ++++++++++++++++++
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:48:5
|
LL | fn while_inifinite() -> bool {
| ---- expected `bool` because of return type
LL | / while true {
LL | |
LL | |
LL | | return true;
LL | | }
| |_____^ expected `bool`, found `()`
|
= note: `while` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `bool` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:57:5
|
LL | fn while_finite() -> bool {
| ---- expected `bool` because of return type
LL | let mut i = 0;
LL | / while i < 3 {
LL | |
LL | | i += 1;
LL | | return true;
LL | | }
| |_____^ expected `bool`, found `()`
|
= note: `while` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `bool` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:65:5
|
LL | fn while_zero_times() -> bool {
| ---- expected `bool` because of return type
LL | / while false {
LL | |
LL | | return true;
LL | | }
| |_____^ expected `bool`, found `()`
|
= note: `while` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `bool` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:72:5
|
LL | fn while_never_type() -> ! {
| - expected `!` because of return type
LL | / while true {
LL | |
LL | |
LL | | }
| |_____^ expected `!`, found `()`
|
= note: expected type `!`
found unit type `()`
= note: `while` loops evaluate to unit type `()`
help: consider adding a diverging expression here
|
LL ~ }
LL + /* `loop {}` or `panic!("...")` */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:94:9
|
LL | / for i in 0..5 {
LL | |
LL | |
LL | | }
| |_________^ expected `usize`, found `()`
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `usize` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:101:9
|
LL | / while false {
LL | |
LL | | }
| |_________^ expected `usize`, found `()`
|
= note: `while` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL + /* `usize` value */
|
error[E0308]: mismatched types
--> $DIR/coerce-loop-issue-122561.rs:107:23
|
LL | let _ = |a: &[(); for x in 0..2 {}]| {};
| ^^^^^^^^^^^^^^^^ expected `usize`, found `()`
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL | let _ = |a: &[(); for x in 0..2 {} /* `usize` value */]| {};
| +++++++++++++++++++
error: aborting due to 18 previous errors; 2 warnings emitted
Some errors have detailed explanations: E0308, E0658.
For more information about an error, try `rustc --explain E0308`.

3
tests/ui/did_you_mean/compatible-variants.stderr
View File

@ -11,6 +11,7 @@ LL | | }
|
= note: expected enum `Option<()>`
found unit type `()`
= note: `while` loops evaluate to unit type `()`
help: try adding an expression at the end of the block
|
LL ~ }
@ -49,6 +50,7 @@ LL | | }
|
= note: expected enum `Option<()>`
found unit type `()`
= note: `for` loops evaluate to unit type `()`
help: try adding an expression at the end of the block
|
LL ~ }
@ -106,6 +108,7 @@ LL | while false {}
|
= note: expected enum `Option<()>`
found unit type `()`
= note: `while` loops evaluate to unit type `()`
help: try adding an expression at the end of the block
|
LL ~ while false {}

18
tests/ui/for-loop-while/break-while-condition.stderr
View File

@ -20,6 +20,12 @@ LL | | }
|
= note: expected type `!`
found unit type `()`
= note: `while` loops evaluate to unit type `()`
help: consider adding a diverging expression here
|
LL ~ }
LL + /* `loop {}` or `panic!("...")` */
|
error[E0308]: mismatched types
--> $DIR/break-while-condition.rs:24:13
@ -31,14 +37,12 @@ LL | | }
|
= note: expected type `!`
found unit type `()`
note: the function expects a value to always be returned, but loops might run zero times
--> $DIR/break-while-condition.rs:24:13
= note: `while` loops evaluate to unit type `()`
help: consider adding a diverging expression here
|
LL ~ }
LL + /* `loop {}` or `panic!("...")` */
|
LL | while false {
| ^^^^^^^^^^^ this might have zero elements to iterate on
LL | return
| ------ if the loop doesn't execute, this value would never get returned
= help: return a value for the case when the loop has zero elements to iterate on, otherwise consider changing the return type to account for that possibility
error: aborting due to 3 previous errors

2
tests/ui/issues/issue-27042.stderr
View File

@ -40,6 +40,8 @@ error[E0308]: mismatched types
LL | / 'c:
LL | | for _ in None { break }; // but here we cite the whole loop
| |_______________________________^ expected `i32`, found `()`
|
= note: `for` loops evaluate to unit type `()`
error[E0308]: mismatched types
--> $DIR/issue-27042.rs:15:9

6
tests/ui/issues/issue-50585.stderr
View File

@ -13,6 +13,12 @@ error[E0308]: mismatched types
|
LL | |y: Vec<[(); for x in 0..2 {}]>| {};
| ^^^^^^^^^^^^^^^^ expected `usize`, found `()`
|
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL | |y: Vec<[(); for x in 0..2 {} /* `usize` value */]>| {};
| +++++++++++++++++++
error: aborting due to 2 previous errors

4
tests/ui/typeck/issue-100285.rs
View File

@ -1,4 +1,4 @@
fn foo(n: i32) -> i32 { //~ HELP otherwise consider changing the return type to account for that possibility
fn foo(n: i32) -> i32 {
for i in 0..0 { //~ ERROR mismatched types [E0308]
if n < 0 {
return i;
@ -14,7 +14,7 @@ fn foo(n: i32) -> i32 { //~ HELP otherwise consider changing the return type to
return 5;
}
} //~ HELP return a value for the case when the loop has zero elements to iterate on
} //~ HELP consider returning a value here
}
fn main() {}

39
tests/ui/typeck/issue-100285.stderr
View File

@ -12,47 +12,12 @@ LL | |
LL | | }
| |_____^ expected `i32`, found `()`
|
note: the function expects a value to always be returned, but loops might run zero times
--> $DIR/issue-100285.rs:2:5
|
LL | for i in 0..0 {
| ^^^^^^^^^^^^^ this might have zero elements to iterate on
LL | if n < 0 {
LL | return i;
| -------- if the loop doesn't execute, this value would never get returned
LL | } else if n < 10 {
LL | return 1;
| -------- if the loop doesn't execute, this value would never get returned
LL | } else if n < 20 {
LL | return 2;
| -------- if the loop doesn't execute, this value would never get returned
= note: if the loop doesn't execute, 3 other values would never get returned
help: return a value for the case when the loop has zero elements to iterate on
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL ~ /* `i32` value */
|
help: otherwise consider changing the return type to account for that possibility
|
LL ~ fn foo(n: i32) -> Option<i32> {
LL | for i in 0..0 {
LL | if n < 0 {
LL ~ return Some(i);
LL | } else if n < 10 {
LL ~ return Some(1);
LL | } else if n < 20 {
LL ~ return Some(2);
LL | } else if n < 30 {
LL ~ return Some(3);
LL | } else if n < 40 {
LL ~ return Some(4);
LL | } else {
LL ~ return Some(5);
LL | }
LL |
LL ~ }
LL ~ None
|
error: aborting due to 1 previous error

4
tests/ui/typeck/issue-98982.rs
View File

@ -1,7 +1,7 @@
fn foo() -> i32 { //~ HELP otherwise consider changing the return type to account for that possibility
fn foo() -> i32 {
for i in 0..0 { //~ ERROR mismatched types [E0308]
return i;
} //~ HELP return a value for the case when the loop has zero elements to iterate on
} //~ HELP consider returning a value here
}
fn main() {}

18
tests/ui/typeck/issue-98982.stderr
View File

@ -8,26 +8,12 @@ LL | | return i;
LL | | }
| |_____^ expected `i32`, found `()`
|
note: the function expects a value to always be returned, but loops might run zero times
--> $DIR/issue-98982.rs:2:5
|
LL | for i in 0..0 {
| ^^^^^^^^^^^^^ this might have zero elements to iterate on
LL | return i;
| -------- if the loop doesn't execute, this value would never get returned
help: return a value for the case when the loop has zero elements to iterate on
= note: `for` loops evaluate to unit type `()`
help: consider returning a value here
|
LL ~ }
LL ~ /* `i32` value */
|
help: otherwise consider changing the return type to account for that possibility
|
LL ~ fn foo() -> Option<i32> {
LL | for i in 0..0 {
LL ~ return Some(i);
LL ~ }
LL ~ None
|
error: aborting due to 1 previous error