[rustc.git] / compiler / rustc_mir_build / src / build / block.rs

use crate::build::ForGuard::OutsideGuard;
use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
use rustc_middle::middle::region::Scope;
use rustc_middle::thir::*;
use rustc_middle::{mir::*, ty};
use rustc_span::Span;

impl<'a, 'tcx> Builder<'a, 'tcx> {
    pub(crate) fn ast_block(
        &mut self,
        destination: Place<'tcx>,
        block: BasicBlock,
        ast_block: BlockId,
        source_info: SourceInfo,
    ) -> BlockAnd<()> {
        let Block { region_scope, span, ref stmts, expr, targeted_by_break, safety_mode: _ } =
            self.thir[ast_block];
        self.in_scope((region_scope, source_info), LintLevel::Inherited, move |this| {
            if targeted_by_break {
                this.in_breakable_scope(None, destination, span, |this| {
                    Some(this.ast_block_stmts(destination, block, span, stmts, expr, region_scope))
                })
            } else {
                this.ast_block_stmts(destination, block, span, stmts, expr, region_scope)
            }
        })
    }

    fn ast_block_stmts(
        &mut self,
        destination: Place<'tcx>,
        mut block: BasicBlock,
        span: Span,
        stmts: &[StmtId],
        expr: Option<ExprId>,
        region_scope: Scope,
    ) -> BlockAnd<()> {
        let this = self;

        // This convoluted structure is to avoid using recursion as we walk down a list
        // of statements. Basically, the structure we get back is something like:
        //
        //    let x = <init> in {
        //       expr1;
        //       let y = <init> in {
        //           expr2;
        //           expr3;
        //           ...
        //       }
        //    }
        //
        // The let bindings are valid till the end of block so all we have to do is to pop all
        // the let-scopes at the end.
        //
        // First we build all the statements in the block.
        let mut let_scope_stack = Vec::with_capacity(8);
        let outer_source_scope = this.source_scope;
        // This scope information is kept for breaking out of the parent remainder scope in case
        // one let-else pattern matching fails.
        // By doing so, we can be sure that even temporaries that receive extended lifetime
        // assignments are dropped, too.
        let mut last_remainder_scope = region_scope;

        let source_info = this.source_info(span);
        for stmt in stmts {
            let Stmt { ref kind } = this.thir[*stmt];
            match kind {
                StmtKind::Expr { scope, expr } => {
                    this.block_context.push(BlockFrame::Statement { ignores_expr_result: true });
                    let si = (*scope, source_info);
                    unpack!(
                        block = this.in_scope(si, LintLevel::Inherited, |this| {
                            this.stmt_expr(block, *expr, Some(*scope))
                        })
                    );
                }
                StmtKind::Let {
                    remainder_scope,
                    init_scope,
                    pattern,
                    initializer: Some(initializer),
                    lint_level,
                    else_block: Some(else_block),
                    span: _,
                } => {
                    // When lowering the statement `let <pat> = <expr> else { <else> };`,
                    // the `<else>` block is nested in the parent scope enclosing this statement.
                    // That scope is usually either the enclosing block scope,
                    // or the remainder scope of the last statement.
                    // This is to make sure that temporaries instantiated in `<expr>` are dropped
                    // as well.
                    // In addition, even though bindings in `<pat>` only come into scope if
                    // the pattern matching passes, in the MIR building the storages for them
                    // are declared as live any way.
                    // This is similar to `let x;` statements without an initializer expression,
                    // where the value of `x` in this example may or may be assigned,
                    // because the storage for their values may not be live after all due to
                    // failure in pattern matching.
                    // For this reason, we declare those storages as live but we do not schedule
                    // any drop yet- they are scheduled later after the pattern matching.
                    // The generated MIR will have `StorageDead` whenever the control flow breaks out
                    // of the parent scope, regardless of the result of the pattern matching.
                    // However, the drops are inserted in MIR only when the control flow breaks out of
                    // the scope of the remainder scope associated with this `let .. else` statement.
                    // Pictorial explanation of the scope structure:
                    // ┌─────────────────────────────────┐
                    // │  Scope of the enclosing block,  │
                    // │  or the last remainder scope    │
                    // │  ┌───────────────────────────┐  │
                    // │  │  Scope for <else> block   │  │
                    // │  └───────────────────────────┘  │
                    // │  ┌───────────────────────────┐  │
                    // │  │  Remainder scope of       │  │
                    // │  │  this let-else statement  │  │
                    // │  │  ┌─────────────────────┐  │  │
                    // │  │  │ <expr> scope        │  │  │
                    // │  │  └─────────────────────┘  │  │
                    // │  │  extended temporaries in  │  │
                    // │  │  <expr> lives in this     │  │
                    // │  │  scope                    │  │
                    // │  │  ┌─────────────────────┐  │  │
                    // │  │  │ Scopes for the rest │  │  │
                    // │  │  └─────────────────────┘  │  │
                    // │  └───────────────────────────┘  │
                    // └─────────────────────────────────┘
                    // Generated control flow:
                    //          │ let Some(x) = y() else { return; }
                    //          │
                    // ┌────────▼───────┐
                    // │ evaluate y()   │
                    // └────────┬───────┘
                    //          │              ┌────────────────┐
                    // ┌────────▼───────┐      │Drop temporaries│
                    // │Test the pattern├──────►in y()          │
                    // └────────┬───────┘      │because breaking│
                    //          │              │out of <expr>   │
                    // ┌────────▼───────┐      │scope           │
                    // │Move value into │      └───────┬────────┘
                    // │binding x       │              │
                    // └────────┬───────┘      ┌───────▼────────┐
                    //          │              │Drop extended   │
                    // ┌────────▼───────┐      │temporaries in  │
                    // │Drop temporaries│      │<expr> because  │
                    // │in y()          │      │breaking out of │
                    // │because breaking│      │remainder scope │
                    // │out of <expr>   │      └───────┬────────┘
                    // │scope           │              │
                    // └────────┬───────┘      ┌───────▼────────┐
                    //          │              │Enter <else>    ├────────►
                    // ┌────────▼───────┐      │block           │ return;
                    // │Continue...     │      └────────────────┘
                    // └────────────────┘

                    let ignores_expr_result = matches!(pattern.kind, PatKind::Wild);
                    this.block_context.push(BlockFrame::Statement { ignores_expr_result });

                    // Lower the `else` block first because its parent scope is actually
                    // enclosing the rest of the `let .. else ..` parts.
                    let else_block_span = this.thir[*else_block].span;
                    // This place is not really used because this destination place
                    // should never be used to take values at the end of the failure
                    // block.
                    let dummy_place = this.temp(this.tcx.types.never, else_block_span);
                    let failure_entry = this.cfg.start_new_block();
                    let failure_block;
                    unpack!(
                        failure_block = this.ast_block(
                            dummy_place,
                            failure_entry,
                            *else_block,
                            this.source_info(else_block_span),
                        )
                    );
                    this.cfg.terminate(
                        failure_block,
                        this.source_info(else_block_span),
                        TerminatorKind::Unreachable,
                    );

                    // Declare the bindings, which may create a source scope.
                    let remainder_span = remainder_scope.span(this.tcx, this.region_scope_tree);
                    this.push_scope((*remainder_scope, source_info));
                    let_scope_stack.push(remainder_scope);

                    let visibility_scope =
                        Some(this.new_source_scope(remainder_span, LintLevel::Inherited));

                    let initializer_span = this.thir[*initializer].span;
                    let scope = (*init_scope, source_info);
                    let failure = unpack!(
                        block = this.in_scope(scope, *lint_level, |this| {
                            this.declare_bindings(
                                visibility_scope,
                                remainder_span,
                                pattern,
                                None,
                                Some((Some(&destination), initializer_span)),
                            );
                            this.visit_primary_bindings(
                                pattern,
                                UserTypeProjections::none(),
                                &mut |this, _, _, node, span, _, _| {
                                    this.storage_live_binding(
                                        block,
                                        node,
                                        span,
                                        OutsideGuard,
                                        true,
                                    );
                                },
                            );
                            this.ast_let_else(
                                block,
                                *initializer,
                                initializer_span,
                                *else_block,
                                &last_remainder_scope,
                                pattern,
                            )
                        })
                    );
                    this.cfg.goto(failure, source_info, failure_entry);

                    if let Some(source_scope) = visibility_scope {
                        this.source_scope = source_scope;
                    }
                    last_remainder_scope = *remainder_scope;
                }
                StmtKind::Let { init_scope, initializer: None, else_block: Some(_), .. } => {
                    span_bug!(
                        init_scope.span(this.tcx, this.region_scope_tree),
                        "initializer is missing, but else block is present in this let binding",
                    )
                }
                StmtKind::Let {
                    remainder_scope,
                    init_scope,
                    ref pattern,
                    initializer,
                    lint_level,
                    else_block: None,
                    span: _,
                } => {
                    let ignores_expr_result = matches!(pattern.kind, PatKind::Wild);
                    this.block_context.push(BlockFrame::Statement { ignores_expr_result });

                    // Enter the remainder scope, i.e., the bindings' destruction scope.
                    this.push_scope((*remainder_scope, source_info));
                    let_scope_stack.push(remainder_scope);

                    // Declare the bindings, which may create a source scope.
                    let remainder_span = remainder_scope.span(this.tcx, this.region_scope_tree);

                    let visibility_scope =
                        Some(this.new_source_scope(remainder_span, LintLevel::Inherited));

                    // Evaluate the initializer, if present.
                    if let Some(init) = *initializer {
                        let initializer_span = this.thir[init].span;
                        let scope = (*init_scope, source_info);

                        unpack!(
                            block = this.in_scope(scope, *lint_level, |this| {
                                this.declare_bindings(
                                    visibility_scope,
                                    remainder_span,
                                    pattern,
                                    None,
                                    Some((None, initializer_span)),
                                );
                                this.expr_into_pattern(block, &pattern, init)
                                // irrefutable pattern
                            })
                        )
                    } else {
                        let scope = (*init_scope, source_info);
                        unpack!(this.in_scope(scope, *lint_level, |this| {
                            this.declare_bindings(
                                visibility_scope,
                                remainder_span,
                                pattern,
                                None,
                                None,
                            );
                            block.unit()
                        }));

                        debug!("ast_block_stmts: pattern={:?}", pattern);
                        this.visit_primary_bindings(
                            pattern,
                            UserTypeProjections::none(),
                            &mut |this, _, _, node, span, _, _| {
                                this.storage_live_binding(block, node, span, OutsideGuard, true);
                                this.schedule_drop_for_binding(node, span, OutsideGuard);
                            },
                        )
                    }

                    // Enter the visibility scope, after evaluating the initializer.
                    if let Some(source_scope) = visibility_scope {
                        this.source_scope = source_scope;
                    }
                    last_remainder_scope = *remainder_scope;
                }
            }

            let popped = this.block_context.pop();
            assert!(popped.is_some_and(|bf| bf.is_statement()));
        }

        // Then, the block may have an optional trailing expression which is a “return” value
        // of the block, which is stored into `destination`.
        let tcx = this.tcx;
        let destination_ty = destination.ty(&this.local_decls, tcx).ty;
        if let Some(expr_id) = expr {
            let expr = &this.thir[expr_id];
            let tail_result_is_ignored =
                destination_ty.is_unit() || this.block_context.currently_ignores_tail_results();
            this.block_context
                .push(BlockFrame::TailExpr { tail_result_is_ignored, span: expr.span });

            unpack!(block = this.expr_into_dest(destination, block, expr_id));
            let popped = this.block_context.pop();

            assert!(popped.is_some_and(|bf| bf.is_tail_expr()));
        } else {
            // If a block has no trailing expression, then it is given an implicit return type.
            // This return type is usually `()`, unless the block is diverging, in which case the
            // return type is `!`. For the unit type, we need to actually return the unit, but in
            // the case of `!`, no return value is required, as the block will never return.
            // Opaque types of empty bodies also need this unit assignment, in order to infer that their
            // type is actually unit. Otherwise there will be no defining use found in the MIR.
            if destination_ty.is_unit()
                || matches!(destination_ty.kind(), ty::Alias(ty::Opaque, ..))
            {
                // We only want to assign an implicit `()` as the return value of the block if the
                // block does not diverge. (Otherwise, we may try to assign a unit to a `!`-type.)
                this.cfg.push_assign_unit(block, source_info, destination, this.tcx);
            }
        }
        // Finally, we pop all the let scopes before exiting out from the scope of block
        // itself.
        for scope in let_scope_stack.into_iter().rev() {
            unpack!(block = this.pop_scope((*scope, source_info), block));
        }
        // Restore the original source scope.
        this.source_scope = outer_source_scope;
        block.unit()
    }
}
Commit	Line	Data
dfeec247 XL	1	use crate::build::ForGuard::OutsideGuard;
dfeec247 XL	2	use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
f2b60f7d	3	use rustc_middle::middle::region::Scope;
17df50a5	4	use rustc_middle::thir::*;
5e7ed085	5	use rustc_middle::{mir::*, ty};
dfeec247	6	use rustc_span::Span;
e9174d1e	7
dc9dc135	8	impl<'a, 'tcx> Builder<'a, 'tcx> {
923072b8	9	pub(crate) fn ast_block(
dfeec247	10	&mut self,
ba9703b0	11	destination: Place<'tcx>,
dfeec247	12	block: BasicBlock,
f2b60f7d	13	ast_block: BlockId,
dfeec247 XL	14	source_info: SourceInfo,
dfeec247 XL	15	) -> BlockAnd<()> {
e8be2606	16	let Block { region_scope, span, ref stmts, expr, targeted_by_break, safety_mode: _ } =
4b012472	17	self.thir[ast_block];
4b012472 FG	18	self.in_scope((region_scope, source_info), LintLevel::Inherited, move \|this\| {
	19	if targeted_by_break {
	20	this.in_breakable_scope(None, destination, span, \|this\| {
e8be2606	21	Some(this.ast_block_stmts(destination, block, span, stmts, expr, region_scope))
4b012472 FG	22	})
4b012472 FG	23	} else {
e8be2606	24	this.ast_block_stmts(destination, block, span, stmts, expr, region_scope)
4b012472	25	}
cc61c64b XL	26	})
cc61c64b XL	27	}
3157f602	28
dfeec247 XL	29	fn ast_block_stmts(
dfeec247 XL	30	&mut self,
ba9703b0	31	destination: Place<'tcx>,
dfeec247 XL	32	mut block: BasicBlock,
dfeec247 XL	33	span: Span,
17df50a5	34	stmts: &[StmtId],
c0240ec0	35	expr: Option<ExprId>,
f2b60f7d	36	region_scope: Scope,
dfeec247	37	) -> BlockAnd<()> {
cc61c64b XL	38	let this = self;
	39
	40	// This convoluted structure is to avoid using recursion as we walk down a list
	41	// of statements. Basically, the structure we get back is something like:
	42	//
	43	// let x = <init> in {
	44	// expr1;
	45	// let y = <init> in {
	46	// expr2;
	47	// expr3;
	48	// ...
	49	// }
	50	// }
	51	//
	52	// The let bindings are valid till the end of block so all we have to do is to pop all
	53	// the let-scopes at the end.
	54	//
	55	// First we build all the statements in the block.
ea8adc8c	56	let mut let_scope_stack = Vec::with_capacity(8);
94b46f34	57	let outer_source_scope = this.source_scope;
f2b60f7d FG	58	// This scope information is kept for breaking out of the parent remainder scope in case
	59	// one let-else pattern matching fails.
	60	// By doing so, we can be sure that even temporaries that receive extended lifetime
	61	// assignments are dropped, too.
	62	let mut last_remainder_scope = region_scope;
ea8adc8c	63
041b39d2	64	let source_info = this.source_info(span);
17df50a5	65	for stmt in stmts {
4b012472	66	let Stmt { ref kind } = this.thir[*stmt];
cc61c64b	67	match kind {
17df50a5	68	StmtKind::Expr { scope, expr } => {
0bf4aa26	69	this.block_context.push(BlockFrame::Statement { ignores_expr_result: true });
4b012472	70	let si = (*scope, source_info);
dfeec247	71	unpack!(
4b012472	72	block = this.in_scope(si, LintLevel::Inherited, \|this\| {
c0240ec0	73	this.stmt_expr(block, expr, Some(scope))
4b012472	74	})
dfeec247	75	);
cc61c64b	76	}
f2b60f7d FG	77	StmtKind::Let {
	78	remainder_scope,
	79	init_scope,
	80	pattern,
	81	initializer: Some(initializer),
	82	lint_level,
	83	else_block: Some(else_block),
353b0b11	84	span: _,
f2b60f7d FG	85	} => {
f2b60f7d FG	86	// When lowering the statement `let <pat> = <expr> else { <else> };`,
487cf647	87	// the `<else>` block is nested in the parent scope enclosing this statement.
f2b60f7d FG	88	// That scope is usually either the enclosing block scope,
	89	// or the remainder scope of the last statement.
	90	// This is to make sure that temporaries instantiated in `<expr>` are dropped
	91	// as well.
	92	// In addition, even though bindings in `<pat>` only come into scope if
	93	// the pattern matching passes, in the MIR building the storages for them
	94	// are declared as live any way.
	95	// This is similar to `let x;` statements without an initializer expression,
	96	// where the value of `x` in this example may or may be assigned,
	97	// because the storage for their values may not be live after all due to
	98	// failure in pattern matching.
	99	// For this reason, we declare those storages as live but we do not schedule
	100	// any drop yet- they are scheduled later after the pattern matching.
	101	// The generated MIR will have `StorageDead` whenever the control flow breaks out
	102	// of the parent scope, regardless of the result of the pattern matching.
	103	// However, the drops are inserted in MIR only when the control flow breaks out of
	104	// the scope of the remainder scope associated with this `let .. else` statement.
	105	// Pictorial explanation of the scope structure:
	106	// ┌─────────────────────────────────┐
	107	// │ Scope of the enclosing block, │
	108	// │ or the last remainder scope │
	109	// │ ┌───────────────────────────┐ │
	110	// │ │ Scope for <else> block │ │
	111	// │ └───────────────────────────┘ │
	112	// │ ┌───────────────────────────┐ │
	113	// │ │ Remainder scope of │ │
	114	// │ │ this let-else statement │ │
	115	// │ │ ┌─────────────────────┐ │ │
	116	// │ │ │ <expr> scope │ │ │
	117	// │ │ └─────────────────────┘ │ │
	118	// │ │ extended temporaries in │ │
	119	// │ │ <expr> lives in this │ │
	120	// │ │ scope │ │
	121	// │ │ ┌─────────────────────┐ │ │
	122	// │ │ │ Scopes for the rest │ │ │
	123	// │ │ └─────────────────────┘ │ │
	124	// │ └───────────────────────────┘ │
	125	// └─────────────────────────────────┘
	126	// Generated control flow:
	127	// │ let Some(x) = y() else { return; }
	128	// │
	129	// ┌────────▼───────┐
	130	// │ evaluate y() │
	131	// └────────┬───────┘
	132	// │ ┌────────────────┐
	133	// ┌────────▼───────┐ │Drop temporaries│
	134	// │Test the pattern├──────►in y() │
	135	// └────────┬───────┘ │because breaking│
	136	// │ │out of <expr> │
	137	// ┌────────▼───────┐ │scope │
	138	// │Move value into │ └───────┬────────┘
	139	// │binding x │ │
	140	// └────────┬───────┘ ┌───────▼────────┐
	141	// │ │Drop extended │
	142	// ┌────────▼───────┐ │temporaries in │
	143	// │Drop temporaries│ │<expr> because │
	144	// │in y() │ │breaking out of │
	145	// │because breaking│ │remainder scope │
	146	// │out of <expr> │ └───────┬────────┘
	147	// │scope │ │
	148	// └────────┬───────┘ ┌───────▼────────┐
	149	// │ │Enter <else> ├────────►
	150	// ┌────────▼───────┐ │block │ return;
	151	// │Continue... │ └────────────────┘
152	// └────────────────┘
153
154	let ignores_expr_result = matches!(pattern.kind, PatKind::Wild);
155	this.block_context.push(BlockFrame::Statement { ignores_expr_result });
156
157	// Lower the `else` block first because its parent scope is actually
158	// enclosing the rest of the `let .. else ..` parts.
159	let else_block_span = this.thir[*else_block].span;
160	// This place is not really used because this destination place
161	// should never be used to take values at the end of the failure
162	// block.
163	let dummy_place = this.temp(this.tcx.types.never, else_block_span);
164	let failure_entry = this.cfg.start_new_block();
165	let failure_block;
166	unpack!(
167	failure_block = this.ast_block(
168	dummy_place,
169	failure_entry,
170	*else_block,
171	this.source_info(else_block_span),
172	)
173	);
174	this.cfg.terminate(
175	failure_block,
176	this.source_info(else_block_span),
177	TerminatorKind::Unreachable,
178	);
179
180	// Declare the bindings, which may create a source scope.
181	let remainder_span = remainder_scope.span(this.tcx, this.region_scope_tree);
182	this.push_scope((*remainder_scope, source_info));
183	let_scope_stack.push(remainder_scope);
184
185	let visibility_scope =
e8be2606	186	Some(this.new_source_scope(remainder_span, LintLevel::Inherited));
f2b60f7d	187
c0240ec0	188	let initializer_span = this.thir[*initializer].span;
4b012472	189	let scope = (*init_scope, source_info);
f2b60f7d	190	let failure = unpack!(
4b012472 FG	191	block = this.in_scope(scope, *lint_level, \|this\| {
	192	this.declare_bindings(
	193	visibility_scope,
	194	remainder_span,
	195	pattern,
	196	None,
	197	Some((Some(&destination), initializer_span)),
	198	);
	199	this.visit_primary_bindings(
	200	pattern,
	201	UserTypeProjections::none(),
e8be2606	202	&mut \|this, _, _, node, span, _, _\| {
4b012472	203	this.storage_live_binding(
f2b60f7d	204	block,
4b012472 FG	205	node,
	206	span,
	207	OutsideGuard,
	208	true,
	209	);
	210	},
	211	);
	212	this.ast_let_else(
	213	block,
c0240ec0	214	*initializer,
4b012472 FG	215	initializer_span,
	216	*else_block,
	217	&last_remainder_scope,
	218	pattern,
	219	)
	220	})
f2b60f7d FG	221	);
	222	this.cfg.goto(failure, source_info, failure_entry);
	223
	224	if let Some(source_scope) = visibility_scope {
	225	this.source_scope = source_scope;
	226	}
	227	last_remainder_scope = *remainder_scope;
	228	}
	229	StmtKind::Let { init_scope, initializer: None, else_block: Some(_), .. } => {
	230	span_bug!(
	231	init_scope.span(this.tcx, this.region_scope_tree),
	232	"initializer is missing, but else block is present in this let binding",
	233	)
	234	}
17df50a5 XL	235	StmtKind::Let {
	236	remainder_scope,
	237	init_scope,
	238	ref pattern,
	239	initializer,
	240	lint_level,
f2b60f7d	241	else_block: None,
353b0b11	242	span: _,
17df50a5	243	} => {
f2b60f7d	244	let ignores_expr_result = matches!(pattern.kind, PatKind::Wild);
0bf4aa26 XL	245	this.block_context.push(BlockFrame::Statement { ignores_expr_result });
0bf4aa26 XL	246
0731742a	247	// Enter the remainder scope, i.e., the bindings' destruction scope.
6a06907d	248	this.push_scope((*remainder_scope, source_info));
ea8adc8c	249	let_scope_stack.push(remainder_scope);
3157f602	250
94b46f34	251	// Declare the bindings, which may create a source scope.
6a06907d	252	let remainder_span = remainder_scope.span(this.tcx, this.region_scope_tree);
8faf50e0	253
dc9dc135	254	let visibility_scope =
e8be2606	255	Some(this.new_source_scope(remainder_span, LintLevel::Inherited));
3157f602	256
cc61c64b	257	// Evaluate the initializer, if present.
c0240ec0 FG	258	if let Some(init) = *initializer {
c0240ec0 FG	259	let initializer_span = this.thir[init].span;
4b012472	260	let scope = (*init_scope, source_info);
8faf50e0	261
dfeec247	262	unpack!(
4b012472 FG	263	block = this.in_scope(scope, *lint_level, \|this\| {
	264	this.declare_bindings(
	265	visibility_scope,
	266	remainder_span,
	267	pattern,
	268	None,
	269	Some((None, initializer_span)),
	270	);
	271	this.expr_into_pattern(block, &pattern, init)
	272	// irrefutable pattern
	273	})
064997fb	274	)
cc61c64b	275	} else {
6a06907d XL	276	let scope = (*init_scope, source_info);
6a06907d XL	277	unpack!(this.in_scope(scope, *lint_level, \|this\| {
dc9dc135 XL	278	this.declare_bindings(
	279	visibility_scope,
	280	remainder_span,
6a06907d	281	pattern,
487cf647	282	None,
dc9dc135 XL	283	None,
	284	);
	285	block.unit()
	286	}));
8faf50e0	287
0731742a	288	debug!("ast_block_stmts: pattern={:?}", pattern);
f9f354fc	289	this.visit_primary_bindings(
17df50a5	290	pattern,
0731742a	291	UserTypeProjections::none(),
e8be2606	292	&mut \|this, _, _, node, span, _, _\| {
74b04a01	293	this.storage_live_binding(block, node, span, OutsideGuard, true);
0bf4aa26	294	this.schedule_drop_for_binding(node, span, OutsideGuard);
dfeec247 XL	295	},
dfeec247 XL	296	)
cc61c64b XL	297	}
cc61c64b XL	298
dc9dc135 XL	299	// Enter the visibility scope, after evaluating the initializer.
dc9dc135 XL	300	if let Some(source_scope) = visibility_scope {
94b46f34	301	this.source_scope = source_scope;
54a0048b	302	}
f2b60f7d	303	last_remainder_scope = *remainder_scope;
9cc50fc6 SL	304	}
9cc50fc6 SL	305	}
0bf4aa26 XL	306
0bf4aa26 XL	307	let popped = this.block_context.pop();
49aad941	308	assert!(popped.is_some_and(\|bf\| bf.is_statement()));
cc61c64b	309	}
0bf4aa26	310
cc61c64b	311	// Then, the block may have an optional trailing expression which is a “return” value
0bf4aa26	312	// of the block, which is stored into `destination`.
6a06907d	313	let tcx = this.tcx;
532ac7d7	314	let destination_ty = destination.ty(&this.local_decls, tcx).ty;
c0240ec0 FG	315	if let Some(expr_id) = expr {
c0240ec0 FG	316	let expr = &this.thir[expr_id];
dfeec247 XL	317	let tail_result_is_ignored =
dfeec247 XL	318	destination_ty.is_unit() \|\| this.block_context.currently_ignores_tail_results();
6a06907d XL	319	this.block_context
6a06907d XL	320	.push(BlockFrame::TailExpr { tail_result_is_ignored, span: expr.span });
0bf4aa26	321
c0240ec0	322	unpack!(block = this.expr_into_dest(destination, block, expr_id));
0bf4aa26 XL	323	let popped = this.block_context.pop();
0bf4aa26 XL	324
49aad941	325	assert!(popped.is_some_and(\|bf\| bf.is_tail_expr()));
cc61c64b	326	} else {
2c00a5a8 XL	327	// If a block has no trailing expression, then it is given an implicit return type.
	328	// This return type is usually `()`, unless the block is diverging, in which case the
	329	// return type is `!`. For the unit type, we need to actually return the unit, but in
	330	// the case of `!`, no return value is required, as the block will never return.
5e7ed085 FG	331	// Opaque types of empty bodies also need this unit assignment, in order to infer that their
5e7ed085 FG	332	// type is actually unit. Otherwise there will be no defining use found in the MIR.
9c376795 FG	333	if destination_ty.is_unit()
	334	\|\| matches!(destination_ty.kind(), ty::Alias(ty::Opaque, ..))
	335	{
2c00a5a8 XL	336	// We only want to assign an implicit `()` as the return value of the block if the
2c00a5a8 XL	337	// block does not diverge. (Otherwise, we may try to assign a unit to a `!`-type.)
6a06907d	338	this.cfg.push_assign_unit(block, source_info, destination, this.tcx);
2c00a5a8	339	}
cc61c64b XL	340	}
	341	// Finally, we pop all the let scopes before exiting out from the scope of block
	342	// itself.
ea8adc8c	343	for scope in let_scope_stack.into_iter().rev() {
6a06907d	344	unpack!(block = this.pop_scope((*scope, source_info), block));
cc61c64b	345	}
94b46f34 XL	346	// Restore the original source scope.
94b46f34 XL	347	this.source_scope = outer_source_scope;
cc61c64b	348	block.unit()
e9174d1e SL	349	}
e9174d1e SL	350	}