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Auto merge of #68965 - eddyb:mir-inline-scope, r=nagisa,oli-obk

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rustc_mir: track inlined callees in SourceScopeData.

We now record which MIR scopes are the roots of *other* (inlined) functions's scope trees, which allows us to generate the correct debuginfo in codegen, similar to what LLVM inlining generates.
This PR makes the `ui` test `backtrace-debuginfo` pass, if the MIR inliner is turned on by default.

Also, `#[track_caller]` is now correct in the face of MIR inlining (cc `@anp).`

Fixes #76997.

r? `@rust-lang/wg-mir-opt`
This commit is contained in:
bors 2020-10-26 18:50:22 +00:00
commit 0da6d42f29
68 changed files with 879 additions and 619 deletions
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79
compiler/rustc_mir/src/interpret/intrinsics/caller_location.rs
View file

@ -15,38 +15,61 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
/// Walks up the callstack from the intrinsic's callsite, searching for the first callsite in a
/// frame which is not `#[track_caller]`.
crate fn find_closest_untracked_caller_location(&self) -> Span {
let frame = self
.stack()
.iter()
.rev()
// Find first non-`#[track_caller]` frame.
.find(|frame| {
for frame in self.stack().iter().rev() {
debug!("find_closest_untracked_caller_location: checking frame {:?}", frame.instance);
// Assert that the frame we look at is actually executing code currently
// (`loc` is `Err` when we are unwinding and the frame does not require cleanup).
let loc = frame.loc.unwrap();
// This could be a non-`Call` terminator (such as `Drop`), or not a terminator at all
// (such as `box`). Use the normal span by default.
let mut source_info = *frame.body.source_info(loc);
// If this is a `Call` terminator, use the `fn_span` instead.
let block = &frame.body.basic_blocks()[loc.block];
if loc.statement_index == block.statements.len() {
debug!(
"find_closest_untracked_caller_location: checking frame {:?}",
frame.instance
"find_closest_untracked_caller_location: got terminator {:?} ({:?})",
block.terminator(),
block.terminator().kind
);
!frame.instance.def.requires_caller_location(*self.tcx)
})
// Assert that there is always such a frame.
.unwrap();
// Assert that the frame we look at is actually executing code currently
// (`loc` is `Err` when we are unwinding and the frame does not require cleanup).
let loc = frame.loc.unwrap();
// If this is a `Call` terminator, use the `fn_span` instead.
let block = &frame.body.basic_blocks()[loc.block];
if loc.statement_index == block.statements.len() {
debug!(
"find_closest_untracked_caller_location:: got terminator {:?} ({:?})",
block.terminator(),
block.terminator().kind
);
if let TerminatorKind::Call { fn_span, .. } = block.terminator().kind {
return fn_span;
if let TerminatorKind::Call { fn_span, .. } = block.terminator().kind {
source_info.span = fn_span;
}
}
// Walk up the `SourceScope`s, in case some of them are from MIR inlining.
// If so, the starting `source_info.span` is in the innermost inlined
// function, and will be replaced with outer callsite spans as long
// as the inlined functions were `#[track_caller]`.
loop {
let scope_data = &frame.body.source_scopes[source_info.scope];
if let Some((callee, callsite_span)) = scope_data.inlined {
// Stop inside the most nested non-`#[track_caller]` function,
// before ever reaching its caller (which is irrelevant).
if !callee.def.requires_caller_location(*self.tcx) {
return source_info.span;
}
source_info.span = callsite_span;
}
// Skip past all of the parents with `inlined: None`.
match scope_data.inlined_parent_scope {
Some(parent) => source_info.scope = parent,
None => break,
}
}
// Stop inside the most nested non-`#[track_caller]` function,
// before ever reaching its caller (which is irrelevant).
if !frame.instance.def.requires_caller_location(*self.tcx) {
return source_info.span;
}
}
// This is a different terminator (such as `Drop`) or not a terminator at all
// (such as `box`). Use the normal span.
frame.body.source_info(loc).span
bug!("no non-`#[track_caller]` frame found")
}
/// Allocate a `const core::panic::Location` with the provided filename and line/column numbers.

8
compiler/rustc_mir/src/shim.rs
View file

@ -212,7 +212,13 @@ fn new_body<'tcx>(
source,
basic_blocks,
IndexVec::from_elem_n(
SourceScopeData { span, parent_scope: None, local_data: ClearCrossCrate::Clear },
SourceScopeData {
span,
parent_scope: None,
inlined: None,
inlined_parent_scope: None,
local_data: ClearCrossCrate::Clear,
},
1,
),
local_decls,

2
compiler/rustc_mir/src/transform/const_prop.rs
View file

@ -313,7 +313,7 @@ struct ConstPropagator<'mir, 'tcx> {
param_env: ParamEnv<'tcx>,
// FIXME(eddyb) avoid cloning these two fields more than once,
// by accessing them through `ecx` instead.
source_scopes: IndexVec<SourceScope, SourceScopeData>,
source_scopes: IndexVec<SourceScope, SourceScopeData<'tcx>>,
local_decls: IndexVec<Local, LocalDecl<'tcx>>,
// Because we have `MutVisitor` we can't obtain the `SourceInfo` from a `Location`. So we store
// the last known `SourceInfo` here and just keep revisiting it.

244
compiler/rustc_mir/src/transform/inline.rs
View file

@ -1,13 +1,12 @@
//! Inlining pass for MIR functions
use rustc_attr as attr;
use rustc_hir::def_id::DefId;
use rustc_index::bit_set::BitSet;
use rustc_index::vec::{Idx, IndexVec};
use rustc_index::vec::Idx;
use rustc_middle::middle::codegen_fn_attrs::{CodegenFnAttrFlags, CodegenFnAttrs};
use rustc_middle::mir::visit::*;
use rustc_middle::mir::*;
use rustc_middle::ty::subst::{Subst, SubstsRef};
use rustc_middle::ty::subst::Subst;
use rustc_middle::ty::{self, ConstKind, Instance, InstanceDef, ParamEnv, Ty, TyCtxt};
use rustc_target::spec::abi::Abi;
@ -15,6 +14,7 @@ use super::simplify::{remove_dead_blocks, CfgSimplifier};
use crate::transform::MirPass;
use std::collections::VecDeque;
use std::iter;
use std::ops::RangeFrom;
const DEFAULT_THRESHOLD: usize = 50;
const HINT_THRESHOLD: usize = 100;
@ -30,10 +30,9 @@ pub struct Inline;
#[derive(Copy, Clone, Debug)]
struct CallSite<'tcx> {
callee: DefId,
substs: SubstsRef<'tcx>,
callee: Instance<'tcx>,
bb: BasicBlock,
location: SourceInfo,
source_info: SourceInfo,
}
impl<'tcx> MirPass<'tcx> for Inline {
@ -101,14 +100,20 @@ impl Inliner<'tcx> {
local_change = false;
while let Some(callsite) = callsites.pop_front() {
debug!("checking whether to inline callsite {:?}", callsite);
if !self.tcx.is_mir_available(callsite.callee) {
debug!("checking whether to inline callsite {:?} - MIR unavailable", callsite);
continue;
if let InstanceDef::Item(_) = callsite.callee.def {
if !self.tcx.is_mir_available(callsite.callee.def_id()) {
debug!(
"checking whether to inline callsite {:?} - MIR unavailable",
callsite,
);
continue;
}
}
let callee_body = if let Some(callee_def_id) = callsite.callee.as_local() {
let callee_body = if let Some(callee_def_id) = callsite.callee.def_id().as_local() {
let callee_hir_id = self.tcx.hir().local_def_id_to_hir_id(callee_def_id);
// Avoid a cycle here by only using `optimized_mir` only if we have
// Avoid a cycle here by only using `instance_mir` only if we have
// a lower `HirId` than the callee. This ensures that the callee will
// not inline us. This trick only works without incremental compilation.
// So don't do it if that is enabled. Also avoid inlining into generators,
@ -119,19 +124,21 @@ impl Inliner<'tcx> {
&& self_hir_id < callee_hir_id
&& caller_body.generator_kind.is_none()
{
self.tcx.optimized_mir(callsite.callee)
self.tcx.instance_mir(callsite.callee.def)
} else {
continue;
}
} else {
// This cannot result in a cycle since the callee MIR is from another crate
// and is already optimized.
self.tcx.optimized_mir(callsite.callee)
self.tcx.instance_mir(callsite.callee.def)
};
let callee_body: &Body<'tcx> = &*callee_body;
let callee_body = if self.consider_optimizing(callsite, callee_body) {
self.tcx.subst_and_normalize_erasing_regions(
&callsite.substs,
&callsite.callee.substs,
self.param_env,
callee_body,
)
@ -204,21 +211,16 @@ impl Inliner<'tcx> {
// To resolve an instance its substs have to be fully normalized, so
// we do this here.
let normalized_substs = self.tcx.normalize_erasing_regions(self.param_env, substs);
let instance =
let callee =
Instance::resolve(self.tcx, self.param_env, callee_def_id, normalized_substs)
.ok()
.flatten()?;
if let InstanceDef::Virtual(..) = instance.def {
if let InstanceDef::Virtual(..) | InstanceDef::Intrinsic(_) = callee.def {
return None;
}
return Some(CallSite {
callee: instance.def_id(),
substs: instance.substs,
bb,
location: terminator.source_info,
});
return Some(CallSite { callee, bb, source_info: terminator.source_info });
}
}
@ -243,12 +245,7 @@ impl Inliner<'tcx> {
return false;
}
let codegen_fn_attrs = tcx.codegen_fn_attrs(callsite.callee);
if codegen_fn_attrs.flags.contains(CodegenFnAttrFlags::TRACK_CALLER) {
debug!("`#[track_caller]` present - not inlining");
return false;
}
let codegen_fn_attrs = tcx.codegen_fn_attrs(callsite.callee.def_id());
let self_features = &self.codegen_fn_attrs.target_features;
let callee_features = &codegen_fn_attrs.target_features;
@ -282,8 +279,8 @@ impl Inliner<'tcx> {
// Only inline local functions if they would be eligible for cross-crate
// inlining. This is to ensure that the final crate doesn't have MIR that
// reference unexported symbols
if callsite.callee.is_local() {
if callsite.substs.non_erasable_generics().count() == 0 && !hinted {
if callsite.callee.def_id().is_local() {
if callsite.callee.substs.non_erasable_generics().count() == 0 && !hinted {
debug!(" callee is an exported function - not inlining");
return false;
}
@ -336,7 +333,7 @@ impl Inliner<'tcx> {
work_list.push(target);
// If the place doesn't actually need dropping, treat it like
// a regular goto.
let ty = place.ty(callee_body, tcx).subst(tcx, callsite.substs).ty;
let ty = place.ty(callee_body, tcx).subst(tcx, callsite.callee.substs).ty;
if ty.needs_drop(tcx, self.param_env) {
cost += CALL_PENALTY;
if let Some(unwind) = unwind {
@ -399,7 +396,7 @@ impl Inliner<'tcx> {
for v in callee_body.vars_and_temps_iter() {
let v = &callee_body.local_decls[v];
let ty = v.ty.subst(tcx, callsite.substs);
let ty = v.ty.subst(tcx, callsite.callee.substs);
// Cost of the var is the size in machine-words, if we know
// it.
if let Some(size) = type_size_of(tcx, self.param_env, ty) {
@ -435,36 +432,6 @@ impl Inliner<'tcx> {
TerminatorKind::Call { args, destination: Some(destination), cleanup, .. } => {
debug!("inlined {:?} into {:?}", callsite.callee, caller_body.source);
let mut local_map = IndexVec::with_capacity(callee_body.local_decls.len());
let mut scope_map = IndexVec::with_capacity(callee_body.source_scopes.len());
for mut scope in callee_body.source_scopes.iter().cloned() {
if scope.parent_scope.is_none() {
scope.parent_scope = Some(callsite.location.scope);
// FIXME(eddyb) is this really needed?
// (also note that it's always overwritten below)
scope.span = callee_body.span;
}
// FIXME(eddyb) this doesn't seem right at all.
// The inlined source scopes should probably be annotated as
// such, but also contain all of the original information.
scope.span = callsite.location.span;
let idx = caller_body.source_scopes.push(scope);
scope_map.push(idx);
}
for loc in callee_body.vars_and_temps_iter() {
let mut local = callee_body.local_decls[loc].clone();
local.source_info.scope = scope_map[local.source_info.scope];
local.source_info.span = callsite.location.span;
let idx = caller_body.local_decls.push(local);
local_map.push(idx);
}
// If the call is something like `a[*i] = f(i)`, where
// `i : &mut usize`, then just duplicating the `a[*i]`
// Place could result in two different locations if `f`
@ -491,13 +458,13 @@ impl Inliner<'tcx> {
let ty = dest.ty(caller_body, self.tcx);
let temp = LocalDecl::new(ty, callsite.location.span);
let temp = LocalDecl::new(ty, callsite.source_info.span);
let tmp = caller_body.local_decls.push(temp);
let tmp = Place::from(tmp);
let stmt = Statement {
source_info: callsite.location,
source_info: callsite.source_info,
kind: StatementKind::Assign(box (tmp, dest)),
};
caller_body[callsite.bb].statements.push(stmt);
@ -511,12 +478,11 @@ impl Inliner<'tcx> {
// Copy the arguments if needed.
let args: Vec<_> = self.make_call_args(args, &callsite, caller_body, return_block);
let bb_len = caller_body.basic_blocks().len();
let mut integrator = Integrator {
block_idx: bb_len,
args: &args,
local_map,
scope_map,
new_locals: Local::new(caller_body.local_decls.len())..,
new_scopes: SourceScope::new(caller_body.source_scopes.len())..,
new_blocks: BasicBlock::new(caller_body.basic_blocks().len())..,
destination: dest,
return_block,
cleanup_block: cleanup,
@ -524,22 +490,51 @@ impl Inliner<'tcx> {
tcx: self.tcx,
};
for mut var_debug_info in callee_body.var_debug_info.drain(..) {
integrator.visit_var_debug_info(&mut var_debug_info);
caller_body.var_debug_info.push(var_debug_info);
// Map all `Local`s, `SourceScope`s and `BasicBlock`s to new ones
// (or existing ones, in a few special cases) in the caller.
integrator.visit_body(&mut callee_body);
for scope in &mut callee_body.source_scopes {
// FIXME(eddyb) move this into a `fn visit_scope_data` in `Integrator`.
if scope.parent_scope.is_none() {
let callsite_scope = &caller_body.source_scopes[callsite.source_info.scope];
// Attach the outermost callee scope as a child of the callsite
// scope, via the `parent_scope` and `inlined_parent_scope` chains.
scope.parent_scope = Some(callsite.source_info.scope);
assert_eq!(scope.inlined_parent_scope, None);
scope.inlined_parent_scope = if callsite_scope.inlined.is_some() {
Some(callsite.source_info.scope)
} else {
callsite_scope.inlined_parent_scope
};
// Mark the outermost callee scope as an inlined one.
assert_eq!(scope.inlined, None);
scope.inlined = Some((callsite.callee, callsite.source_info.span));
} else if scope.inlined_parent_scope.is_none() {
// Make it easy to find the scope with `inlined` set above.
scope.inlined_parent_scope =
Some(integrator.map_scope(OUTERMOST_SOURCE_SCOPE));
}
}
for (bb, mut block) in callee_body.basic_blocks_mut().drain_enumerated(..) {
integrator.visit_basic_block_data(bb, &mut block);
caller_body.basic_blocks_mut().push(block);
}
// Insert all of the (mapped) parts of the callee body into the caller.
caller_body.local_decls.extend(
// FIXME(eddyb) make `Range<Local>` iterable so that we can use
// `callee_body.local_decls.drain(callee_body.vars_and_temps())`
callee_body
.vars_and_temps_iter()
.map(|local| callee_body.local_decls[local].clone()),
);
caller_body.source_scopes.extend(callee_body.source_scopes.drain(..));
caller_body.var_debug_info.extend(callee_body.var_debug_info.drain(..));
caller_body.basic_blocks_mut().extend(callee_body.basic_blocks_mut().drain(..));
let terminator = Terminator {
source_info: callsite.location,
kind: TerminatorKind::Goto { target: BasicBlock::new(bb_len) },
};
caller_body[callsite.bb].terminator = Some(terminator);
caller_body[callsite.bb].terminator = Some(Terminator {
source_info: callsite.source_info,
kind: TerminatorKind::Goto { target: integrator.map_block(START_BLOCK) },
});
true
}
@ -583,7 +578,9 @@ impl Inliner<'tcx> {
// tmp2 = tuple_tmp.2
//
// and the vector is `[closure_ref, tmp0, tmp1, tmp2]`.
if tcx.is_closure(callsite.callee) {
// FIXME(eddyb) make this check for `"rust-call"` ABI combined with
// `callee_body.spread_arg == None`, instead of special-casing closures.
if tcx.is_closure(callsite.callee.def_id()) {
let mut args = args.into_iter();
let self_ = self.create_temp_if_necessary(
args.next().unwrap(),
@ -654,20 +651,23 @@ impl Inliner<'tcx> {
let ty = arg.ty(caller_body, self.tcx);
let arg_tmp = LocalDecl::new(ty, callsite.location.span);
let arg_tmp = LocalDecl::new(ty, callsite.source_info.span);
let arg_tmp = caller_body.local_decls.push(arg_tmp);
caller_body[callsite.bb].statements.push(Statement {
source_info: callsite.location,
source_info: callsite.source_info,
kind: StatementKind::StorageLive(arg_tmp),
});
caller_body[callsite.bb].statements.push(Statement {
source_info: callsite.location,
source_info: callsite.source_info,
kind: StatementKind::Assign(box (Place::from(arg_tmp), arg)),
});
caller_body[return_block].statements.insert(
0,
Statement { source_info: callsite.location, kind: StatementKind::StorageDead(arg_tmp) },
Statement {
source_info: callsite.source_info,
kind: StatementKind::StorageDead(arg_tmp),
},
);
arg_tmp
@ -690,10 +690,10 @@ fn type_size_of<'tcx>(
* stuff.
*/
struct Integrator<'a, 'tcx> {
block_idx: usize,
args: &'a [Local],
local_map: IndexVec<Local, Local>,
scope_map: IndexVec<SourceScope, SourceScope>,
new_locals: RangeFrom<Local>,
new_scopes: RangeFrom<SourceScope>,
new_blocks: RangeFrom<BasicBlock>,
destination: Place<'tcx>,
return_block: BasicBlock,
cleanup_block: Option<BasicBlock>,
@ -702,23 +702,31 @@ struct Integrator<'a, 'tcx> {
}
impl<'a, 'tcx> Integrator<'a, 'tcx> {
fn update_target(&self, tgt: BasicBlock) -> BasicBlock {
let new = BasicBlock::new(tgt.index() + self.block_idx);
debug!("updating target `{:?}`, new: `{:?}`", tgt, new);
fn map_local(&self, local: Local) -> Local {
let new = if local == RETURN_PLACE {
self.destination.local
} else {
let idx = local.index() - 1;
if idx < self.args.len() {
self.args[idx]
} else {
Local::new(self.new_locals.start.index() + (idx - self.args.len()))
}
};
debug!("mapping local `{:?}` to `{:?}`", local, new);
new
}
fn make_integrate_local(&self, local: Local) -> Local {
if local == RETURN_PLACE {
return self.destination.local;
}
fn map_scope(&self, scope: SourceScope) -> SourceScope {
let new = SourceScope::new(self.new_scopes.start.index() + scope.index());
debug!("mapping scope `{:?}` to `{:?}`", scope, new);
new
}
let idx = local.index() - 1;
if idx < self.args.len() {
return self.args[idx];
}
self.local_map[Local::new(idx - self.args.len())]
fn map_block(&self, block: BasicBlock) -> BasicBlock {
let new = BasicBlock::new(self.new_blocks.start.index() + block.index());
debug!("mapping block `{:?}` to `{:?}`", block, new);
new
}
}
@ -728,7 +736,11 @@ impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
}
fn visit_local(&mut self, local: &mut Local, _ctxt: PlaceContext, _location: Location) {
*local = self.make_integrate_local(*local);
*local = self.map_local(*local);
}
fn visit_source_scope(&mut self, scope: &mut SourceScope) {
*scope = self.map_scope(*scope);
}
fn visit_place(&mut self, place: &mut Place<'tcx>, context: PlaceContext, location: Location) {
@ -772,18 +784,18 @@ impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
match terminator.kind {
TerminatorKind::GeneratorDrop | TerminatorKind::Yield { .. } => bug!(),
TerminatorKind::Goto { ref mut target } => {
*target = self.update_target(*target);
*target = self.map_block(*target);
}
TerminatorKind::SwitchInt { ref mut targets, .. } => {
for tgt in targets.all_targets_mut() {
*tgt = self.update_target(*tgt);
*tgt = self.map_block(*tgt);
}
}
TerminatorKind::Drop { ref mut target, ref mut unwind, .. }
| TerminatorKind::DropAndReplace { ref mut target, ref mut unwind, .. } => {
*target = self.update_target(*target);
*target = self.map_block(*target);
if let Some(tgt) = *unwind {
*unwind = Some(self.update_target(tgt));
*unwind = Some(self.map_block(tgt));
} else if !self.in_cleanup_block {
// Unless this drop is in a cleanup block, add an unwind edge to
// the original call's cleanup block
@ -792,10 +804,10 @@ impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
}
TerminatorKind::Call { ref mut destination, ref mut cleanup, .. } => {
if let Some((_, ref mut tgt)) = *destination {
*tgt = self.update_target(*tgt);
*tgt = self.map_block(*tgt);
}
if let Some(tgt) = *cleanup {
*cleanup = Some(self.update_target(tgt));
*cleanup = Some(self.map_block(tgt));
} else if !self.in_cleanup_block {
// Unless this call is in a cleanup block, add an unwind edge to
// the original call's cleanup block
@ -803,9 +815,9 @@ impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
}
}
TerminatorKind::Assert { ref mut target, ref mut cleanup, .. } => {
*target = self.update_target(*target);
*target = self.map_block(*target);
if let Some(tgt) = *cleanup {
*cleanup = Some(self.update_target(tgt));
*cleanup = Some(self.map_block(tgt));
} else if !self.in_cleanup_block {
// Unless this assert is in a cleanup block, add an unwind edge to
// the original call's cleanup block
@ -823,8 +835,8 @@ impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
TerminatorKind::Abort => {}
TerminatorKind::Unreachable => {}
TerminatorKind::FalseEdge { ref mut real_target, ref mut imaginary_target } => {
*real_target = self.update_target(*real_target);
*imaginary_target = self.update_target(*imaginary_target);
*real_target = self.map_block(*real_target);
*imaginary_target = self.map_block(*imaginary_target);
}
TerminatorKind::FalseUnwind { real_target: _, unwind: _ } =>
// see the ordering of passes in the optimized_mir query.
@ -833,13 +845,9 @@ impl<'a, 'tcx> MutVisitor<'tcx> for Integrator<'a, 'tcx> {
}
TerminatorKind::InlineAsm { ref mut destination, .. } => {
if let Some(ref mut tgt) = *destination {
*tgt = self.update_target(*tgt);
*tgt = self.map_block(*tgt);
}
}
}
}
fn visit_source_scope(&mut self, scope: &mut SourceScope) {
*scope = self.scope_map[*scope];
}
}

32
compiler/rustc_mir/src/util/pretty.rs
View file

@ -548,8 +548,36 @@ fn write_scope_tree(
};
for &child in children {
assert_eq!(body.source_scopes[child].parent_scope, Some(parent));
writeln!(w, "{0:1$}scope {2} {{", "", indent, child.index())?;
let child_data = &body.source_scopes[child];
assert_eq!(child_data.parent_scope, Some(parent));
let (special, span) = if let Some((callee, callsite_span)) = child_data.inlined {
(
format!(
" (inlined {}{})",
if callee.def.requires_caller_location(tcx) { "#[track_caller] " } else { "" },
callee
),
Some(callsite_span),
)
} else {
(String::new(), None)
};
let indented_header = format!("{0:1$}scope {2}{3} {{", "", indent, child.index(), special);
if let Some(span) = span {
writeln!(
w,
"{0:1$} // at {2}",
indented_header,
ALIGN,
tcx.sess.source_map().span_to_string(span),
)?;
} else {
writeln!(w, "{}", indented_header)?;
}
write_scope_tree(tcx, body, scope_tree, w, child, depth + 1)?;
writeln!(w, "{0:1$}}}", "", depth * INDENT.len())?;
}