rustc_metadata: Switch module children decoding to an iterator

Author: petrochenkov

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -35,11 +35,10 @@ use rustc_span::symbol::{kw, Ident, Symbol};
 use rustc_span::{self, BytePos, ExpnId, Pos, Span, SyntaxContext, DUMMY_SP};
 
 use proc_macro::bridge::client::ProcMacro;
-use std::io;
 use std::iter::TrustedLen;
-use std::mem;
 use std::num::NonZeroUsize;
 use std::path::Path;
+use std::{io, iter, mem};
 
 pub(super) use cstore_impl::provide;
 pub use cstore_impl::provide_extern;
@@ -994,60 +993,61 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
     /// including both proper items and reexports.
     /// Module here is understood in name resolution sense - it can be a `mod` item,
     /// or a crate root, or an enum, or a trait.
-    fn for_each_module_child(
+    fn get_module_children(
         self,
         id: DefIndex,
-        mut callback: impl FnMut(ModChild),
-        sess: &Session,
-    ) {
-        if let Some(data) = &self.root.proc_macro_data {
-            // If we are loading as a proc macro, we want to return
-            // the view of this crate as a proc macro crate.
-            if id == CRATE_DEF_INDEX {
-                for def_index in data.macros.decode(self) {
-                    let raw_macro = self.raw_proc_macro(def_index);
-                    let res = Res::Def(
-                        DefKind::Macro(macro_kind(raw_macro)),
-                        self.local_def_id(def_index),
-                    );
-                    let ident = self.item_ident(def_index, sess);
-                    callback(ModChild {
-                        ident,
-                        res,
-                        vis: ty::Visibility::Public,
-                        span: ident.span,
-                        macro_rules: false,
-                    });
+        sess: &'a Session,
+    ) -> impl Iterator<Item = ModChild> + 'a {
+        iter::from_generator(move || {
+            if let Some(data) = &self.root.proc_macro_data {
+                // If we are loading as a proc macro, we want to return
+                // the view of this crate as a proc macro crate.
+                if id == CRATE_DEF_INDEX {
+                    for def_index in data.macros.decode(self) {
+                        let raw_macro = self.raw_proc_macro(def_index);
+                        let res = Res::Def(
+                            DefKind::Macro(macro_kind(raw_macro)),
+                            self.local_def_id(def_index),
+                        );
+                        let ident = self.item_ident(def_index, sess);
+                        yield ModChild {
+                            ident,
+                            res,
+                            vis: ty::Visibility::Public,
+                            span: ident.span,
+                            macro_rules: false,
+                        };
+                    }
                 }
+                return;
             }
-            return;
-        }
 
-        // Iterate over all children.
-        if let Some(children) = self.root.tables.children.get(self, id) {
-            for child_index in children.decode((self, sess)) {
-                let ident = self.item_ident(child_index, sess);
-                let kind = self.def_kind(child_index);
-                let def_id = self.local_def_id(child_index);
-                let res = Res::Def(kind, def_id);
-                let vis = self.get_visibility(child_index);
-                let span = self.get_span(child_index, sess);
-                let macro_rules = match kind {
-                    DefKind::Macro(..) => {
-                        self.root.tables.macro_rules.get(self, child_index).is_some()
-                    }
-                    _ => false,
-                };
+            // Iterate over all children.
+            if let Some(children) = self.root.tables.children.get(self, id) {
+                for child_index in children.decode((self, sess)) {
+                    let ident = self.item_ident(child_index, sess);
+                    let kind = self.def_kind(child_index);
+                    let def_id = self.local_def_id(child_index);
+                    let res = Res::Def(kind, def_id);
+                    let vis = self.get_visibility(child_index);
+                    let span = self.get_span(child_index, sess);
+                    let macro_rules = match kind {
+                        DefKind::Macro(..) => {
+                            self.root.tables.macro_rules.get(self, child_index).is_some()
+                        }
+                        _ => false,
+                    };
 
-                callback(ModChild { ident, res, vis, span, macro_rules });
+                    yield ModChild { ident, res, vis, span, macro_rules };
+                }
             }
-        }
 
-        if let Some(exports) = self.root.tables.module_reexports.get(self, id) {
-            for exp in exports.decode((self, sess)) {
-                callback(exp);
+            if let Some(exports) = self.root.tables.module_reexports.get(self, id) {
+                for exp in exports.decode((self, sess)) {
+                    yield exp;
+                }
             }
-        }
+        })
     }
 
     fn is_ctfe_mir_available(self, id: DefIndex) -> bool {

compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs

@@ -21,7 +21,6 @@ use rustc_span::source_map::{Span, Spanned};
 use rustc_span::symbol::{kw, Symbol};
 
 use rustc_data_structures::sync::Lrc;
-use smallvec::SmallVec;
 use std::any::Any;
 
 use super::{Decodable, DecodeContext, DecodeIterator};
@@ -298,9 +297,7 @@ provide! { tcx, def_id, other, cdata,
         r
     }
     module_children => {
-        let mut result = SmallVec::<[_; 8]>::new();
-        cdata.for_each_module_child(def_id.index, |child| result.push(child), tcx.sess);
-        tcx.arena.alloc_slice(&result)
+        tcx.arena.alloc_from_iter(cdata.get_module_children(def_id.index, tcx.sess))
     }
     defined_lib_features => { cdata.get_lib_features(tcx) }
     stability_implications => {
@@ -503,14 +500,12 @@ impl CStore {
         self.get_crate_data(def.krate).get_visibility(def.index)
     }
 
-    pub fn module_children_untracked(&self, def_id: DefId, sess: &Session) -> Vec<ModChild> {
-        let mut result = vec![];
-        self.get_crate_data(def_id.krate).for_each_module_child(
-            def_id.index,
-            |child| result.push(child),
-            sess,
-        );
-        result
+    pub fn module_children_untracked<'a>(
+        &'a self,
+        def_id: DefId,
+        sess: &'a Session,
+    ) -> impl Iterator<Item = ModChild> + 'a {
+        self.get_crate_data(def_id.krate).get_module_children(def_id.index, sess)
     }
 
     pub fn load_macro_untracked(&self, id: DefId, sess: &Session) -> LoadedMacro {

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -204,7 +204,9 @@ impl<'a> Resolver<'a> {
     }
 
     pub(crate) fn build_reduced_graph_external(&mut self, module: Module<'a>) {
-        for child in self.cstore().module_children_untracked(module.def_id(), self.session) {
+        for child in
+            Vec::from_iter(self.cstore().module_children_untracked(module.def_id(), self.session))
+        {
             let parent_scope = ParentScope::module(module, self);
             BuildReducedGraphVisitor { r: self, parent_scope }
                 .build_reduced_graph_for_external_crate_res(child);

compiler/rustc_resolve/src/lib.rs

@@ -1920,7 +1920,7 @@ impl<'a> Resolver<'a> {
         if let Some(def_id) = def_id.as_local() {
             self.reexport_map.get(&def_id).cloned().unwrap_or_default()
         } else {
-            self.cstore().module_children_untracked(def_id, self.session)
+            self.cstore().module_children_untracked(def_id, self.session).collect()
         }
     }