From 5c3e5af2ed3776755e584530fd8915544292b821 Mon Sep 17 00:00:00 2001
From: Scott McMurray <scottmcm@users.noreply.github.com>
Date: Mon, 3 Apr 2023 14:22:09 -0700
Subject: [PATCH] Doc-comment `IndexVec::from_elem` and use it in a few more
places
---
.../src/type_check/liveness/local_use_map.rs | 4 ++--
compiler/rustc_index/src/vec.rs | 11 +++++++++++
.../src/infer/lexical_region_resolve/mod.rs | 2 +-
compiler/rustc_mir_transform/src/coverage/graph.rs | 5 ++---
compiler/rustc_ty_utils/src/layout.rs | 2 +-
5 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/compiler/rustc_borrowck/src/type_check/liveness/local_use_map.rs b/compiler/rustc_borrowck/src/type_check/liveness/local_use_map.rs
index 8023ef60d20..2c387edfef0 100644
--- a/compiler/rustc_borrowck/src/type_check/liveness/local_use_map.rs
+++ b/compiler/rustc_borrowck/src/type_check/liveness/local_use_map.rs
@@ -63,7 +63,7 @@ impl LocalUseMap {
elements: &RegionValueElements,
body: &Body<'_>,
) -> Self {
- let nones = IndexVec::from_elem_n(None, body.local_decls.len());
+ let nones = IndexVec::from_elem(None, &body.local_decls);
let mut local_use_map = LocalUseMap {
first_def_at: nones.clone(),
first_use_at: nones.clone(),
@@ -76,7 +76,7 @@ impl LocalUseMap {
}
let mut locals_with_use_data: IndexVec<Local, bool> =
- IndexVec::from_elem_n(false, body.local_decls.len());
+ IndexVec::from_elem(false, &body.local_decls);
live_locals.iter().for_each(|&local| locals_with_use_data[local] = true);
LocalUseMapBuild { local_use_map: &mut local_use_map, elements, locals_with_use_data }
diff --git a/compiler/rustc_index/src/vec.rs b/compiler/rustc_index/src/vec.rs
index 5945de2302a..16cf9ae5cfc 100644
--- a/compiler/rustc_index/src/vec.rs
+++ b/compiler/rustc_index/src/vec.rs
@@ -129,6 +129,17 @@ impl<I: Idx, T> IndexVec<I, T> {
IndexVec { raw: Vec::with_capacity(capacity), _marker: PhantomData }
}
+ /// Creates a new vector with a copy of `elem` for each index in `universe`.
+ ///
+ /// Thus `IndexVec::from_elem(elem, &universe)` is equivalent to
+ /// `IndexVec::<I, _>::from_elem_n(elem, universe.len())`. That can help
+ /// type inference as it ensures that the resulting vector uses the same
+ /// index type as `universe`, rather than something potentially surprising.
+ ///
+ /// For example, if you want to store data for each local in a MIR body,
+ /// using `let mut uses = IndexVec::from_elem(vec![], &body.local_decls);`
+ /// ensures that `uses` is an `IndexVec<Local, _>`, and thus can give
+ /// better error messages later if one accidentally mismatches indices.
#[inline]
pub fn from_elem<S>(elem: T, universe: &IndexSlice<I, S>) -> Self
where
diff --git a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
index 9e2bdb7f510..f298b95ca35 100644
--- a/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
+++ b/compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs
@@ -203,7 +203,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
// Tracks the `VarSubVar` constraints generated for each region vid. We
// later use this to expand across vids.
- let mut constraints = IndexVec::from_elem_n(Vec::new(), var_values.values.len());
+ let mut constraints = IndexVec::from_elem(Vec::new(), &var_values.values);
// Tracks the changed region vids.
let mut changes = Vec::new();
for constraint in self.data.constraints.keys() {
diff --git a/compiler/rustc_mir_transform/src/coverage/graph.rs b/compiler/rustc_mir_transform/src/coverage/graph.rs
index 689d6c71361..6a73f2a6578 100644
--- a/compiler/rustc_mir_transform/src/coverage/graph.rs
+++ b/compiler/rustc_mir_transform/src/coverage/graph.rs
@@ -37,8 +37,7 @@ impl CoverageGraph {
// `SwitchInt` to have multiple targets to the same destination `BasicBlock`, so
// de-duplication is required. This is done without reordering the successors.
- let bcbs_len = bcbs.len();
- let mut seen = IndexVec::from_elem_n(false, bcbs_len);
+ let mut seen = IndexVec::from_elem(false, &bcbs);
let successors = IndexVec::from_fn_n(
|bcb| {
for b in seen.iter_mut() {
@@ -60,7 +59,7 @@ impl CoverageGraph {
bcbs.len(),
);
- let mut predecessors = IndexVec::from_elem_n(Vec::new(), bcbs.len());
+ let mut predecessors = IndexVec::from_elem(Vec::new(), &bcbs);
for (bcb, bcb_successors) in successors.iter_enumerated() {
for &successor in bcb_successors {
predecessors[successor].push(bcb);
diff --git a/compiler/rustc_ty_utils/src/layout.rs b/compiler/rustc_ty_utils/src/layout.rs
index 73f86f74d14..e8155520c9b 100644
--- a/compiler/rustc_ty_utils/src/layout.rs
+++ b/compiler/rustc_ty_utils/src/layout.rs
@@ -522,7 +522,7 @@ fn generator_saved_local_eligibility(
use SavedLocalEligibility::*;
let mut assignments: IndexVec<GeneratorSavedLocal, SavedLocalEligibility> =
- IndexVec::from_elem_n(Unassigned, info.field_tys.len());
+ IndexVec::from_elem(Unassigned, &info.field_tys);
// The saved locals not eligible for overlap. These will get
// "promoted" to the prefix of our generator.