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|
use crate::build::matches::ArmHasGuard;
use crate::build::ForGuard::OutsideGuard;
use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder};
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: &Block,
source_info: SourceInfo,
) -> BlockAnd<()> {
let Block {
region_scope,
opt_destruction_scope,
span,
ref stmts,
expr,
targeted_by_break,
safety_mode,
} = *ast_block;
let expr = expr.map(|expr| &self.thir[expr]);
self.in_opt_scope(opt_destruction_scope.map(|de| (de, source_info)), move |this| {
this.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,
safety_mode,
))
})
} else {
this.ast_block_stmts(destination, block, span, &stmts, expr, safety_mode)
}
})
})
}
fn ast_block_stmts(
&mut self,
destination: Place<'tcx>,
mut block: BasicBlock,
span: Span,
stmts: &[StmtId],
expr: Option<&Expr<'tcx>>,
safety_mode: BlockSafety,
) -> 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;
let outer_in_scope_unsafe = this.in_scope_unsafe;
this.update_source_scope_for_safety_mode(span, safety_mode);
let source_info = this.source_info(span);
for stmt in stmts {
let Stmt { ref kind, opt_destruction_scope } = this.thir[*stmt];
match kind {
StmtKind::Expr { scope, expr } => {
this.block_context.push(BlockFrame::Statement { ignores_expr_result: true });
unpack!(
block = this.in_opt_scope(
opt_destruction_scope.map(|de| (de, source_info)),
|this| {
let si = (*scope, source_info);
this.in_scope(si, LintLevel::Inherited, |this| {
this.stmt_expr(block, &this.thir[*expr], Some(*scope))
})
}
)
);
}
StmtKind::Let {
remainder_scope,
init_scope,
ref pattern,
initializer,
lint_level,
else_block,
} => {
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, None));
// Evaluate the initializer, if present.
if let Some(init) = initializer {
let init = &this.thir[*init];
let initializer_span = init.span;
unpack!(
block = this.in_opt_scope(
opt_destruction_scope.map(|de| (de, source_info)),
|this| {
let scope = (*init_scope, source_info);
this.in_scope(scope, *lint_level, |this| {
if let Some(else_block) = else_block {
this.ast_let_else(
block,
init,
initializer_span,
else_block,
visibility_scope,
*remainder_scope,
remainder_span,
pattern,
)
} else {
this.declare_bindings(
visibility_scope,
remainder_span,
pattern,
ArmHasGuard(false),
Some((None, initializer_span)),
);
this.expr_into_pattern(block, pattern.clone(), 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,
ArmHasGuard(false),
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;
}
}
}
let popped = this.block_context.pop();
assert!(popped.map_or(false, |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) = expr {
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));
let popped = this.block_context.pop();
assert!(popped.map_or(false, |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::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;
this.in_scope_unsafe = outer_in_scope_unsafe;
block.unit()
}
/// If we are entering an unsafe block, create a new source scope
fn update_source_scope_for_safety_mode(&mut self, span: Span, safety_mode: BlockSafety) {
debug!("update_source_scope_for({:?}, {:?})", span, safety_mode);
let new_unsafety = match safety_mode {
BlockSafety::Safe => return,
BlockSafety::BuiltinUnsafe => Safety::BuiltinUnsafe,
BlockSafety::ExplicitUnsafe(hir_id) => {
self.in_scope_unsafe = Safety::ExplicitUnsafe(hir_id);
Safety::ExplicitUnsafe(hir_id)
}
};
self.source_scope = self.new_source_scope(span, LintLevel::Inherited, Some(new_unsafety));
}
}
|
