Rollup merge of #80635 - sexxi-goose:use-place-instead-of-symbol, r=nikomatsakis`

Improve diagnostics when closure doesn't meet trait bound

Improves the diagnostics when closure doesn't meet trait bound by modifying `TypeckResuts::closure_kind_origins` such that `hir::Place` is used instead of `Symbol`. Using `hir::Place` to describe which capture influenced the decision of selecting a trait a closure satisfies to (Fn/FnMut/FnOnce, Copy) allows us to show precise path in the diagnostics when `capture_disjoint_field` feature is enabled.

Closes rust-lang/project-rfc-2229/issues/21

r? ```@nikomatsakis```

2 files changed, 46 insertions, 4 deletions

diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index 148ac604596..1f7dc7bb79d 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -3,6 +3,7 @@
 use crate::arena::Arena;
 use crate::dep_graph::DepGraph;
 use crate::hir::exports::ExportMap;
+use crate::hir::place::Place as HirPlace;
 use crate::ich::{NodeIdHashingMode, StableHashingContext};
 use crate::infer::canonical::{Canonical, CanonicalVarInfo, CanonicalVarInfos};
 use crate::lint::{struct_lint_level, LintDiagnosticBuilder, LintLevelSource};
@@ -379,7 +380,7 @@ pub struct TypeckResults<'tcx> {
 
     /// Records the reasons that we picked the kind of each closure;
     /// not all closures are present in the map.
-    closure_kind_origins: ItemLocalMap<(Span, Symbol)>,
+    closure_kind_origins: ItemLocalMap<(Span, HirPlace<'tcx>)>,
 
     /// For each fn, records the "liberated" types of its arguments
     /// and return type. Liberated means that all bound regions
@@ -642,11 +643,13 @@ impl<'tcx> TypeckResults<'tcx> {
         self.upvar_capture_map[&upvar_id]
     }
 
-    pub fn closure_kind_origins(&self) -> LocalTableInContext<'_, (Span, Symbol)> {
+    pub fn closure_kind_origins(&self) -> LocalTableInContext<'_, (Span, HirPlace<'tcx>)> {
         LocalTableInContext { hir_owner: self.hir_owner, data: &self.closure_kind_origins }
     }
 
-    pub fn closure_kind_origins_mut(&mut self) -> LocalTableInContextMut<'_, (Span, Symbol)> {
+    pub fn closure_kind_origins_mut(
+        &mut self,
+    ) -> LocalTableInContextMut<'_, (Span, HirPlace<'tcx>)> {
         LocalTableInContextMut { hir_owner: self.hir_owner, data: &mut self.closure_kind_origins }
     }
 
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 1399fc76e02..b1769b17b42 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -17,7 +17,9 @@ pub use self::IntVarValue::*;
 pub use self::Variance::*;
 
 use crate::hir::exports::ExportMap;
-use crate::hir::place::Place as HirPlace;
+use crate::hir::place::{
+    Place as HirPlace, PlaceBase as HirPlaceBase, ProjectionKind as HirProjectionKind,
+};
 use crate::ich::StableHashingContext;
 use crate::middle::cstore::CrateStoreDyn;
 use crate::middle::resolve_lifetime::ObjectLifetimeDefault;
@@ -734,6 +736,43 @@ pub struct CapturedPlace<'tcx> {
     pub info: CaptureInfo<'tcx>,
 }
 
+pub fn place_to_string_for_capture(tcx: TyCtxt<'tcx>, place: &HirPlace<'tcx>) -> String {
+    let name = match place.base {
+        HirPlaceBase::Upvar(upvar_id) => tcx.hir().name(upvar_id.var_path.hir_id).to_string(),
+        _ => bug!("Capture_information should only contain upvars"),
+    };
+    let mut curr_string = name;
+
+    for (i, proj) in place.projections.iter().enumerate() {
+        match proj.kind {
+            HirProjectionKind::Deref => {
+                curr_string = format!("*{}", curr_string);
+            }
+            HirProjectionKind::Field(idx, variant) => match place.ty_before_projection(i).kind() {
+                ty::Adt(def, ..) => {
+                    curr_string = format!(
+                        "{}.{}",
+                        curr_string,
+                        def.variants[variant].fields[idx as usize].ident.name.as_str()
+                    );
+                }
+                ty::Tuple(_) => {
+                    curr_string = format!("{}.{}", curr_string, idx);
+                }
+                _ => {
+                    bug!(
+                        "Field projection applied to a type other than Adt or Tuple: {:?}.",
+                        place.ty_before_projection(i).kind()
+                    )
+                }
+            },
+            proj => bug!("{:?} unexpected because it isn't captured", proj),
+        }
+    }
+
+    curr_string.to_string()
+}
+
 /// Part of `MinCaptureInformationMap`; describes the capture kind (&, &mut, move)
 /// for a particular capture as well as identifying the part of the source code
 /// that triggered this capture to occur.