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Remove suggestion about iteration count in coerce #123125

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May 5, 2024
Merged

Remove suggestion about iteration count in coerce #123125

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155 changes: 17 additions & 138 deletions compiler/rustc_hir_typeck/src/coercion.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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};
Expand Down Expand Up @@ -95,22 +93,6 @@ 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>(
Expand Down Expand Up @@ -1601,7 +1583,6 @@ 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!(
Expand Down Expand Up @@ -1636,11 +1617,6 @@ 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(
Expand Down Expand Up @@ -1741,6 +1717,22 @@ 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,
Expand All @@ -1749,15 +1741,6 @@ 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);
Expand Down Expand Up @@ -1831,110 +1814,6 @@ 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>,
Expand Down
3 changes: 2 additions & 1 deletion compiler/rustc_hir_typeck/src/demand.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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(
Expand Down
89 changes: 87 additions & 2 deletions compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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(
Expand Down
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