Auto merge of #104730 - petrochenkov:modchild5, r=cjgillot

rustc_metadata: Switch module children decoding to an iterator

Previously https://github.com/rust-lang/rust/pull/103578, https://github.com/rust-lang/rust/pull/103524 and previous PRs simplified it as much as possible.

A couple of cleanup commits is also added.
r? `@cjgillot`

5 files changed, 54 insertions, 82 deletions

diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index 3fae6694add..08d377646d5 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -29,17 +29,16 @@ use rustc_session::cstore::{
     CrateSource, ExternCrate, ForeignModule, LinkagePreference, NativeLib,
 };
 use rustc_session::Session;
-use rustc_span::hygiene::{ExpnIndex, MacroKind};
+use rustc_span::hygiene::ExpnIndex;
 use rustc_span::source_map::{respan, Spanned};
 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;
@@ -984,64 +983,52 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         DiagnosticItems { id_to_name, name_to_id }
     }
 
+    fn get_mod_child(self, id: DefIndex, sess: &Session) -> ModChild {
+        let ident = self.item_ident(id, sess);
+        let kind = self.def_kind(id);
+        let def_id = self.local_def_id(id);
+        let res = Res::Def(kind, def_id);
+        let vis = self.get_visibility(id);
+        let span = self.get_span(id, sess);
+        let macro_rules = match kind {
+            DefKind::Macro(..) => self.root.tables.macro_rules.get(self, id).is_some(),
+            _ => false,
+        };
+
+        ModChild { ident, res, vis, span, macro_rules }
+    }
+
     /// Iterates over all named children of the given module,
     /// 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 child_index in data.macros.decode(self) {
+                        yield self.get_mod_child(child_index, sess);
+                    }
+                }
+            } else {
+                // Iterate over all children.
+                for child_index in self.root.tables.children.get(self, id).unwrap().decode(self) {
+                    yield self.get_mod_child(child_index, sess);
                 }
-            }
-            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()
+                if let Some(reexports) = self.root.tables.module_reexports.get(self, id) {
+                    for reexport in reexports.decode((self, sess)) {
+                        yield reexport;
                     }
-                    _ => false,
-                };
-
-                callback(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);
+                }
             }
-        }
+        })
     }
 
     fn is_ctfe_mir_available(self, id: DefIndex) -> bool {
@@ -1778,13 +1765,3 @@ impl CrateMetadata {
         None
     }
 }
-
-// Cannot be implemented on 'ProcMacro', as libproc_macro
-// does not depend on librustc_ast
-fn macro_kind(raw: &ProcMacro) -> MacroKind {
-    match raw {
-        ProcMacro::CustomDerive { .. } => MacroKind::Derive,
-        ProcMacro::Attr { .. } => MacroKind::Attr,
-        ProcMacro::Bang { .. } => MacroKind::Bang,
-    }
-}
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index d96252ba569..33cce0a411e 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/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 {
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 0602b7fc3bd..8b4c4bb2675 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -1267,13 +1267,6 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         // the crate root for consistency with other crates (some of the resolver
         // code uses it). However, we skip encoding anything relating to child
         // items - we encode information about proc-macros later on.
-        let reexports = if !self.is_proc_macro {
-            tcx.module_reexports(local_def_id).unwrap_or(&[])
-        } else {
-            &[]
-        };
-
-        record_array!(self.tables.module_reexports[def_id] <- reexports);
         if self.is_proc_macro {
             // Encode this here because we don't do it in encode_def_ids.
             record!(self.tables.expn_that_defined[def_id] <- tcx.expn_that_defined(local_def_id));
@@ -1305,6 +1298,11 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                     }
                 }
             }));
+
+            if let Some(reexports) = tcx.module_reexports(local_def_id) {
+                assert!(!reexports.is_empty());
+                record_array!(self.tables.module_reexports[def_id] <- reexports);
+            }
         }
     }
 
diff --git a/compiler/rustc_resolve/src/build_reduced_graph.rs b/compiler/rustc_resolve/src/build_reduced_graph.rs
index fff3f0467df..91ac442431d 100644
--- a/compiler/rustc_resolve/src/build_reduced_graph.rs
+++ b/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);
diff --git a/compiler/rustc_resolve/src/lib.rs b/compiler/rustc_resolve/src/lib.rs
index f9ae3b58172..ad05d4f1446 100644
--- a/compiler/rustc_resolve/src/lib.rs
+++ b/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()
         }
     }