Auto merge of #13431 - GnomedDev:split-def_path_res, r=y21

Split def_path_res into two parts

`def_path_res` previously had two jobs:
1. looking up the crates to find the path in
2. looking up path in said crates

This splits that job up into two functions, keeping `def_path_res` as an adapter between the both, to avoid repeating the first step when repeatedly looking up items in the same crate.

changelog: none

2 files changed, 34 insertions, 21 deletions

diff --git a/clippy_lints/src/regex.rs b/clippy_lints/src/regex.rs
index f6ef02b7c23..12cbdb854ef 100644
--- a/clippy_lints/src/regex.rs
+++ b/clippy_lints/src/regex.rs
@@ -3,7 +3,7 @@ use std::fmt::Display;
 use clippy_utils::consts::{ConstEvalCtxt, Constant};
 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
 use clippy_utils::source::SpanRangeExt;
-use clippy_utils::{def_path_def_ids, path_def_id, paths};
+use clippy_utils::{def_path_res_with_base, find_crates, path_def_id, paths};
 use rustc_ast::ast::{LitKind, StrStyle};
 use rustc_hir::def_id::DefIdMap;
 use rustc_hir::{BorrowKind, Expr, ExprKind};
@@ -75,11 +75,14 @@ impl<'tcx> LateLintPass<'tcx> for Regex {
         // We don't use `match_def_path` here because that relies on matching the exact path, which changed
         // between regex 1.8 and 1.9
         //
-        // `def_path_def_ids` will resolve through re-exports but is relatively heavy, so we only perform
-        // the operation once and store the results
-        let mut resolve = |path, kind| {
-            for id in def_path_def_ids(cx.tcx, path) {
-                self.definitions.insert(id, kind);
+        // `def_path_res_with_base` will resolve through re-exports but is relatively heavy, so we only
+        // perform the operation once and store the results
+        let regex_crates = find_crates(cx.tcx, sym!(regex));
+        let mut resolve = |path: &[&str], kind: RegexKind| {
+            for res in def_path_res_with_base(cx.tcx, regex_crates.clone(), &path[1..]) {
+                if let Some(id) = res.opt_def_id() {
+                    self.definitions.insert(id, kind);
+                }
             }
         };
 
diff --git a/clippy_utils/src/lib.rs b/clippy_utils/src/lib.rs
index a925549b0bf..2fee6473910 100644
--- a/clippy_utils/src/lib.rs
+++ b/clippy_utils/src/lib.rs
@@ -671,6 +671,17 @@ fn item_children_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: Symbol) -> Vec<Re
     }
 }
 
+/// Finds the crates called `name`, may be multiple due to multiple major versions.
+pub fn find_crates(tcx: TyCtxt<'_>, name: Symbol) -> Vec<Res> {
+    tcx.crates(())
+        .iter()
+        .copied()
+        .filter(move |&num| tcx.crate_name(num) == name)
+        .map(CrateNum::as_def_id)
+        .map(|id| Res::Def(tcx.def_kind(id), id))
+        .collect()
+}
+
 /// Resolves a def path like `std::vec::Vec`.
 ///
 /// Can return multiple resolutions when there are multiple versions of the same crate, e.g.
@@ -681,15 +692,7 @@ fn item_children_by_name(tcx: TyCtxt<'_>, def_id: DefId, name: Symbol) -> Vec<Re
 ///
 /// This function is expensive and should be used sparingly.
 pub fn def_path_res(tcx: TyCtxt<'_>, path: &[&str]) -> Vec<Res> {
-    fn find_crates(tcx: TyCtxt<'_>, name: Symbol) -> impl Iterator<Item = DefId> + '_ {
-        tcx.crates(())
-            .iter()
-            .copied()
-            .filter(move |&num| tcx.crate_name(num) == name)
-            .map(CrateNum::as_def_id)
-    }
-
-    let (base, mut path) = match *path {
+    let (base, path) = match *path {
         [primitive] => {
             return vec![PrimTy::from_name(Symbol::intern(primitive)).map_or(Res::Err, Res::PrimTy)];
         },
@@ -705,18 +708,25 @@ pub fn def_path_res(tcx: TyCtxt<'_>, path: &[&str]) -> Vec<Res> {
         None
     };
 
-    let starts = find_primitive_impls(tcx, base)
-        .chain(find_crates(tcx, base_sym))
+    let crates = find_primitive_impls(tcx, base)
         .chain(local_crate)
-        .map(|id| Res::Def(tcx.def_kind(id), id));
+        .map(|id| Res::Def(tcx.def_kind(id), id))
+        .chain(find_crates(tcx, base_sym))
+        .collect();
 
-    let mut resolutions: Vec<Res> = starts.collect();
+    def_path_res_with_base(tcx, crates, path)
+}
 
+/// Resolves a def path like `vec::Vec` with the base `std`.
+///
+/// This is lighter than [`def_path_res`], and should be called with [`find_crates`] looking up
+/// items from the same crate repeatedly, although should still be used sparingly.
+pub fn def_path_res_with_base(tcx: TyCtxt<'_>, mut base: Vec<Res>, mut path: &[&str]) -> Vec<Res> {
     while let [segment, rest @ ..] = path {
         path = rest;
         let segment = Symbol::intern(segment);
 
-        resolutions = resolutions
+        base = base
             .into_iter()
             .filter_map(|res| res.opt_def_id())
             .flat_map(|def_id| {
@@ -735,7 +745,7 @@ pub fn def_path_res(tcx: TyCtxt<'_>, path: &[&str]) -> Vec<Res> {
             .collect();
     }
 
-    resolutions
+    base
 }
 
 /// Resolves a def path like `std::vec::Vec` to its [`DefId`]s, see [`def_path_res`].