Store names of captured variables in optimized_mir

- Closures in external crates may get compiled in because of
  monomorphization. We should store names of captured variables
  in `optimized_mir`, so that they are written into the metadata
  file and we can use them to generate debuginfo.

- If there are breakpoints inside closures, the names of captured
  variables stored in `optimized_mir` can be used to print them.
  Now the name is more precise when disjoint fields are captured.

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -1280,6 +1280,31 @@ fn prepare_struct_metadata(
 // Tuples
 //=-----------------------------------------------------------------------------
 
+/// Returns names of captured upvars for closures and generators.
+///
+/// Here are some examples:
+///  - `name__field1__field2` when the upvar is captured by value.
+///  - `_ref__name__field` when the upvar is captured by reference.
+fn closure_saved_names_of_captured_variables(tcx: TyCtxt<'tcx>, def_id: DefId) -> Vec<String> {
+    let body = tcx.optimized_mir(def_id);
+
+    body.var_debug_info
+        .iter()
+        .filter_map(|var| {
+            let is_ref = match var.value {
+                mir::VarDebugInfoContents::Place(place) if place.local == mir::Local::new(1) => {
+                    // The projection is either `[.., Field, Deref]` or `[.., Field]`. It
+                    // implies whether the variable is captured by value or by reference.
+                    matches!(place.projection.last().unwrap(), mir::ProjectionElem::Deref)
+                }
+                _ => return None,
+            };
+            let prefix = if is_ref { "_ref__" } else { "" };
+            Some(prefix.to_owned() + &var.name.as_str())
+        })
+        .collect::<Vec<_>>()
+}
+
 /// Creates `MemberDescription`s for the fields of a tuple.
 struct TupleMemberDescriptionFactory<'tcx> {
     ty: Ty<'tcx>,
@@ -1289,34 +1314,23 @@ struct TupleMemberDescriptionFactory<'tcx> {
 
 impl<'tcx> TupleMemberDescriptionFactory<'tcx> {
     fn create_member_descriptions(&self, cx: &CodegenCx<'ll, 'tcx>) -> Vec<MemberDescription<'ll>> {
-        // For closures and generators, name the captured upvars
+        let capture_names = match *self.ty.kind() {
-        // with the help of `CapturedPlace::to_mangled_name`.
+            ty::Generator(def_id, ..) | ty::Closure(def_id, ..) => {
-        let closure_def_id = match *self.ty.kind() {
+                Some(closure_saved_names_of_captured_variables(cx.tcx, def_id))
-            ty::Generator(def_id, ..) => def_id.as_local(),
-            ty::Closure(def_id, ..) => def_id.as_local(),
-            _ => None,
-        };
-        let captures = match closure_def_id {
-            Some(local_def_id) => {
-                let typeck_results = cx.tcx.typeck(local_def_id);
-                let captures = typeck_results
-                    .closure_min_captures_flattened(local_def_id.to_def_id())
-                    .collect::<Vec<_>>();
-                Some(captures)
             }
             _ => None,
         };
-
         let layout = cx.layout_of(self.ty);
         self.component_types
             .iter()
             .enumerate()
             .map(|(i, &component_type)| {
                 let (size, align) = cx.size_and_align_of(component_type);
-                let name = captures
+                let name = if let Some(names) = capture_names.as_ref() {
-                    .as_ref()
+                    names[i].clone()
-                    .map(|c| c[i].to_mangled_name(cx.tcx))
+                } else {
-                    .unwrap_or_else(|| format!("__{}", i));
+                    format!("__{}", i)
+                };
                 MemberDescription {
                     name,
                     type_metadata: type_metadata(cx, component_type, self.span),

compiler/rustc_middle/src/ty/closure.rs

@@ -3,10 +3,12 @@ use crate::hir::place::{
 };
 use crate::{mir, ty};
 
+use std::fmt::Write;
+
 use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_span::Span;
+use rustc_span::{Span, Symbol};
 
 use super::{Ty, TyCtxt};
 
@@ -159,37 +161,26 @@ impl CapturedPlace<'tcx> {
         place_to_string_for_capture(tcx, &self.place)
     }
 
-    /// Returns mangled names of captured upvars. Here are some examples:
+    /// Returns a symbol of the captured upvar, which looks like `name__field1__field2`.
-    ///  - `_captured_val__name__field`
+    pub fn to_symbol(&self, tcx: TyCtxt<'tcx>) -> Symbol {
-    ///  - `_captured_ref__name__field`
-    ///
-    /// The purpose is to use those names in debuginfo. They should be human-understandable.
-    /// Without the names, the end users may get confused when the debuggers just print some
-    /// pointers in closures or generators.
-    pub fn to_mangled_name(&self, tcx: TyCtxt<'tcx>) -> String {
-        let prefix = match self.info.capture_kind {
-            ty::UpvarCapture::ByValue(_) => "_captured_val__",
-            ty::UpvarCapture::ByRef(_) => "_captured_ref__",
-        };
-
         let hir_id = match self.place.base {
             HirPlaceBase::Upvar(upvar_id) => upvar_id.var_path.hir_id,
             base => bug!("Expected an upvar, found {:?}", base),
         };
-        let name = tcx.hir().name(hir_id);
+        let mut symbol = tcx.hir().name(hir_id).as_str().to_string();
 
         let mut ty = self.place.base_ty;
-        let mut fields = String::new();
         for proj in self.place.projections.iter() {
             match proj.kind {
                 HirProjectionKind::Field(idx, variant) => match ty.kind() {
-                    ty::Tuple(_) => fields = format!("{}__{}", fields, idx),
+                    ty::Tuple(_) => write!(&mut symbol, "__{}", idx).unwrap(),
                     ty::Adt(def, ..) => {
-                        fields = format!(
+                        write!(
-                            "{}__{}",
+                            &mut symbol,
-                            fields,
+                            "__{}",
                             def.variants[variant].fields[idx as usize].ident.name.as_str(),
-                        );
+                        )
+                        .unwrap();
                     }
                     ty => {
                         bug!("Unexpected type {:?} for `Field` projection", ty)
@@ -204,7 +195,7 @@ impl CapturedPlace<'tcx> {
             ty = proj.ty;
         }
 
-        prefix.to_owned() + &name.to_string() + &fields
+        Symbol::intern(&symbol)
     }
 
     /// Returns the hir-id of the root variable for the captured place.

compiler/rustc_mir_build/src/build/mod.rs

@@ -16,7 +16,7 @@ use rustc_middle::mir::*;
 use rustc_middle::thir::{BindingMode, Expr, ExprId, LintLevel, PatKind, Thir};
 use rustc_middle::ty::subst::Subst;
 use rustc_middle::ty::{self, Ty, TyCtxt, TypeFoldable, TypeckResults};
-use rustc_span::symbol::{kw, sym};
+use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_target::spec::abi::Abi;
 use rustc_target::spec::PanicStrategy;
@@ -974,13 +974,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
                     let mutability = captured_place.mutability;
 
-                    // FIXME(project-rfc-2229#8): Store more precise information
+                    let name = captured_place.to_symbol(tcx);
-                    let mut name = kw::Empty;
-                    if let Some(Node::Binding(pat)) = tcx_hir.find(var_id) {
-                        if let hir::PatKind::Binding(_, _, ident, _) = pat.kind {
-                            name = ident.name;
-                        }
-                    }
 
                     let mut projs = closure_env_projs.clone();
                     projs.push(ProjectionElem::Field(Field::new(i), ty));

src/test/debuginfo/captured-fields-1.rs

@@ -4,38 +4,44 @@
 
 // gdb-command:run
 // gdb-command:print test
-// gdbr-check:$1 = captured_fields::main::{closure#0} {_captured_ref__my_ref__my_field1: 0x[...]}
+// gdbr-check:$1 = captured_fields_1::main::{closure#0} {_ref__my_ref__my_field1: 0x[...]}
 // gdb-command:continue
 // gdb-command:print test
-// gdbr-check:$2 = captured_fields::main::{closure#1} {_captured_ref__my_ref__my_field2: 0x[...]}
+// gdbr-check:$2 = captured_fields_1::main::{closure#1} {_ref__my_ref__my_field2: 0x[...]}
 // gdb-command:continue
 // gdb-command:print test
-// gdbr-check:$3 = captured_fields::main::{closure#2} {_captured_ref__my_ref: 0x[...]}
+// gdbr-check:$3 = captured_fields_1::main::{closure#2} {_ref__my_ref: 0x[...]}
 // gdb-command:continue
 // gdb-command:print test
-// gdbr-check:$4 = captured_fields::main::{closure#3} {_captured_val__my_ref: 0x[...]}
+// gdbr-check:$4 = captured_fields_1::main::{closure#3} {my_ref: 0x[...]}
 // gdb-command:continue
 // gdb-command:print test
-// gdbr-check:$5 = captured_fields::main::{closure#4} {_captured_val__my_var: captured_fields::MyStruct {my_field1: 11, my_field2: 22}}
+// gdbr-check:$5 = captured_fields_1::main::{closure#4} {my_var__my_field2: 22}
+// gdb-command:continue
+// gdb-command:print test
+// gdbr-check:$6 = captured_fields_1::main::{closure#5} {my_var: captured_fields_1::MyStruct {my_field1: 11, my_field2: 22}}
 // gdb-command:continue
 
 // === LLDB TESTS ==================================================================================
 
 // lldb-command:run
 // lldb-command:print test
-// lldbg-check:(captured_fields::main::{closure#0}) $0 = { _captured_ref__my_ref__my_field1 = 0x[...] }
+// lldbg-check:(captured_fields_1::main::{closure#0}) $0 = { _ref__my_ref__my_field1 = 0x[...] }
 // lldb-command:continue
 // lldb-command:print test
-// lldbg-check:(captured_fields::main::{closure#1}) $1 = { _captured_ref__my_ref__my_field2 = 0x[...] }
+// lldbg-check:(captured_fields_1::main::{closure#1}) $1 = { _ref__my_ref__my_field2 = 0x[...] }
 // lldb-command:continue
 // lldb-command:print test
-// lldbg-check:(captured_fields::main::{closure#2}) $2 = { _captured_ref__my_ref = 0x[...] }
+// lldbg-check:(captured_fields_1::main::{closure#2}) $2 = { _ref__my_ref = 0x[...] }
 // lldb-command:continue
 // lldb-command:print test
-// lldbg-check:(captured_fields::main::{closure#3}) $3 = { _captured_val__my_ref = 0x[...] }
+// lldbg-check:(captured_fields_1::main::{closure#3}) $3 = { my_ref = 0x[...] }
 // lldb-command:continue
 // lldb-command:print test
-// lldbg-check:(captured_fields::main::{closure#4}) $4 = { _captured_val__my_var = { my_field1 = 11 my_field2 = 22 } }
+// lldbg-check:(captured_fields_1::main::{closure#4}) $4 = { my_var__my_field2 = 22 }
+// lldb-command:continue
+// lldb-command:print test
+// lldbg-check:(captured_fields_1::main::{closure#5}) $5 = { my_var = { my_field1 = 11 my_field2 = 22 } }
 // lldb-command:continue
 
 #![feature(capture_disjoint_fields)]
@@ -77,6 +83,12 @@ fn main() {
 
     _zzz(); // #break
 
+    let test = move || {
+        let a = my_var.my_field2;
+    };
+
+    _zzz(); // #break
+
     let test = || {
         let a = my_var;
     };

src/test/debuginfo/captured-fields-2.rs

@@ -0,0 +1,55 @@
+// compile-flags:-g
+
+// === GDB TESTS ===================================================================================
+
+// gdb-command:run
+// gdb-command:print my_ref__my_field1
+// gdbr-check:$1 = 11
+// gdb-command:continue
+// gdb-command:print my_var__my_field2
+// gdbr-check:$2 = 22
+// gdb-command:continue
+
+// === LLDB TESTS ==================================================================================
+
+// lldb-command:run
+// lldb-command:print my_ref__my_field1
+// lldbg-check:(unsigned int) $0 = 11
+// lldb-command:continue
+// lldb-command:print my_var__my_field2
+// lldbg-check:(unsigned int) $1 = 22
+// lldb-command:continue
+
+#![feature(capture_disjoint_fields)]
+#![allow(unused)]
+
+struct MyStruct {
+    my_field1: u32,
+    my_field2: u32,
+}
+
+fn main() {
+    let mut my_var = MyStruct {
+        my_field1: 11,
+        my_field2: 22,
+    };
+    let my_ref = &mut my_var;
+
+    let test = || {
+        let a = my_ref.my_field1;
+
+        _zzz(); // #break
+    };
+
+    test();
+
+    let test = move || {
+        let a = my_var.my_field2;
+
+        _zzz(); // #break
+    };
+
+    test();
+}
+
+fn _zzz() {}

src/test/debuginfo/generator-objects.rs

@@ -11,16 +11,16 @@
 
 // gdb-command:run
 // gdb-command:print b
-// gdb-check:$1 = generator_objects::main::{generator#0}::Unresumed{_captured_ref__a: 0x[...]}
+// gdb-check:$1 = generator_objects::main::{generator#0}::Unresumed{_ref__a: 0x[...]}
 // gdb-command:continue
 // gdb-command:print b
-// gdb-check:$2 = generator_objects::main::{generator#0}::Suspend0{c: 6, d: 7, _captured_ref__a: 0x[...]}
+// gdb-check:$2 = generator_objects::main::{generator#0}::Suspend0{c: 6, d: 7, _ref__a: 0x[...]}
 // gdb-command:continue
 // gdb-command:print b
-// gdb-check:$3 = generator_objects::main::{generator#0}::Suspend1{c: 7, d: 8, _captured_ref__a: 0x[...]}
+// gdb-check:$3 = generator_objects::main::{generator#0}::Suspend1{c: 7, d: 8, _ref__a: 0x[...]}
 // gdb-command:continue
 // gdb-command:print b
-// gdb-check:$4 = generator_objects::main::{generator#0}::Returned{_captured_ref__a: 0x[...]}
+// gdb-check:$4 = generator_objects::main::{generator#0}::Returned{_ref__a: 0x[...]}
 
 // === LLDB TESTS ==================================================================================
 

src/test/debuginfo/issue-57822.rs

@@ -11,17 +11,17 @@
 // gdb-command:run
 
 // gdb-command:print g
-// gdb-check:$1 = issue_57822::main::{closure#1} {_captured_val__f: issue_57822::main::{closure#0} {_captured_val__x: 1}}
+// gdb-check:$1 = issue_57822::main::{closure#1} {f: issue_57822::main::{closure#0} {x: 1}}
 
 // gdb-command:print b
-// gdb-check:$2 = issue_57822::main::{generator#3}::Unresumed{_captured_val__a: issue_57822::main::{generator#2}::Unresumed{_captured_val__y: 2}}
+// gdb-check:$2 = issue_57822::main::{generator#3}::Unresumed{a: issue_57822::main::{generator#2}::Unresumed{y: 2}}
 
 // === LLDB TESTS ==================================================================================
 
 // lldb-command:run
 
 // lldb-command:print g
-// lldbg-check:(issue_57822::main::{closure#1}) $0 = { _captured_val__f = { _captured_val__x = 1 } }
+// lldbg-check:(issue_57822::main::{closure#1}) $0 = { f = { x = 1 } }
 
 // lldb-command:print b
 // lldbg-check:(issue_57822::main::{generator#3}) $1 =