bjoernager/rust
bjoernager/rust
1
Fork 0
Code Activity

Avoid nondeterminism in trimmed_def_paths

Browse source 
Previously this query depended on the global interning order of Symbols, which
meant that irrelevant changes could influence the query and cause
recompilations. This commit ensures that the return set is stable and will not
be affected by the global order by deterministically (in lexicographic order)
choosing a name to use if there are multiple names for a single DefId.
This commit is contained in:
Mark Rousskov 2021-09-30 14:25:46 -04:00
parent 69c1c6a173
commit 56fcf0725a
1 changed files with 23 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

25
compiler/rustc_middle/src/ty/print/pretty.rs
View file

@ -2408,7 +2408,7 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
/// ///
/// The implementation uses similar import discovery logic to that of 'use' suggestions. /// The implementation uses similar import discovery logic to that of 'use' suggestions.
fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> FxHashMap<DefId, Symbol> { fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> FxHashMap<DefId, Symbol> {
let mut map = FxHashMap::default(); let mut map: FxHashMap<DefId, Symbol> = FxHashMap::default();
if let TrimmedDefPaths::GoodPath = tcx.sess.opts.trimmed_def_paths { if let TrimmedDefPaths::GoodPath = tcx.sess.opts.trimmed_def_paths {
// For good paths causing this bug, the `rustc_middle::ty::print::with_no_trimmed_paths` // For good paths causing this bug, the `rustc_middle::ty::print::with_no_trimmed_paths`
@ -2446,8 +2446,29 @@ fn trimmed_def_paths(tcx: TyCtxt<'_>, (): ()) -> FxHashMap<DefId, Symbol> {
}); });
for ((_, symbol), opt_def_id) in unique_symbols_rev.drain() { for ((_, symbol), opt_def_id) in unique_symbols_rev.drain() {
use std::collections::hash_map::Entry::{Occupied, Vacant};
if let Some(def_id) = opt_def_id { if let Some(def_id) = opt_def_id {
map.insert(def_id, symbol); match map.entry(def_id) {
Occupied(mut v) => {
// A single DefId can be known under multiple names (e.g.,
// with a `pub use ... as ...;`). We need to ensure that the
// name placed in this map is chosen deterministically, so
// if we find multiple names (`symbol`) resolving to the
// same `def_id`, we prefer the lexicographically smallest
// name.
//
// Any stable ordering would be fine here though.
if *v.get() != symbol {
if v.get().as_str() > symbol.as_str() {
v.insert(symbol);
}
}
}
Vacant(v) => {
v.insert(symbol);
}
}
} }
} }