Auto merge of #38024 - jseyfried:avoid_needless_proc_macro_deps, r=nrc

Avoid loading needless proc-macro dependencies

Fixes #37958 when no proc-macros are exported; in particular, without `pub extern crate proc_macros;`, `#![feature(macro_reexport)]`, or `#![feature(use_extern_macros)]`.

I opened https://github.com/rust-lang/cargo/issues/3334 for exported proc macros.

r? @alexcrichton

4 files changed, 22 insertions, 21 deletions

diff --git a/src/librustc_metadata/creader.rs b/src/librustc_metadata/creader.rs
index 372152d2b0a..2c266068fe8 100644
--- a/src/librustc_metadata/creader.rs
+++ b/src/librustc_metadata/creader.rs
@@ -171,7 +171,7 @@ impl<'a> CrateLoader<'a> {
                     name: name,
                     id: i.id,
                     dep_kind: if attr::contains_name(&i.attrs, "no_link") {
-                        DepKind::MacrosOnly
+                        DepKind::UnexportedMacrosOnly
                     } else {
                         DepKind::Explicit
                     },
@@ -350,7 +350,7 @@ impl<'a> CrateLoader<'a> {
             };
 
             self.load(&mut locate_ctxt).or_else(|| {
-                dep_kind = DepKind::MacrosOnly;
+                dep_kind = DepKind::UnexportedMacrosOnly;
 
                 let mut proc_macro_locator = locator::Context {
                     target: &self.sess.host,
@@ -373,7 +373,7 @@ impl<'a> CrateLoader<'a> {
             LoadResult::Previous(cnum) => {
                 let data = self.cstore.get_crate_data(cnum);
                 if data.root.macro_derive_registrar.is_some() {
-                    dep_kind = DepKind::MacrosOnly;
+                    dep_kind = DepKind::UnexportedMacrosOnly;
                 }
                 data.dep_kind.set(cmp::max(data.dep_kind.get(), dep_kind));
                 (cnum, data)
@@ -460,11 +460,14 @@ impl<'a> CrateLoader<'a> {
             return cstore::CrateNumMap::new();
         }
 
-        // The map from crate numbers in the crate we're resolving to local crate
-        // numbers
-        let deps = crate_root.crate_deps.decode(metadata);
-        let map: FxHashMap<_, _> = deps.enumerate().map(|(crate_num, dep)| {
+        // The map from crate numbers in the crate we're resolving to local crate numbers.
+        // We map 0 and all other holes in the map to our parent crate. The "additional"
+        // self-dependencies should be harmless.
+        ::std::iter::once(krate).chain(crate_root.crate_deps.decode(metadata).map(|dep| {
             debug!("resolving dep crate {} hash: `{}`", dep.name, dep.hash);
+            if dep.kind == DepKind::UnexportedMacrosOnly {
+                return krate;
+            }
             let dep_kind = match dep_kind {
                 DepKind::MacrosOnly => DepKind::MacrosOnly,
                 _ => dep.kind,
@@ -472,16 +475,8 @@ impl<'a> CrateLoader<'a> {
             let (local_cnum, ..) = self.resolve_crate(
                 root, dep.name, dep.name, Some(&dep.hash), span, PathKind::Dependency, dep_kind,
             );
-            (CrateNum::new(crate_num + 1), local_cnum)
-        }).collect();
-
-        let max_cnum = map.values().cloned().max().map(|cnum| cnum.as_u32()).unwrap_or(0);
-
-        // we map 0 and all other holes in the map to our parent crate. The "additional"
-        // self-dependencies should be harmless.
-        (0..max_cnum+1).map(|cnum| {
-            map.get(&CrateNum::from_u32(cnum)).cloned().unwrap_or(krate)
-        }).collect()
+            local_cnum
+        })).collect()
     }
 
     fn read_extension_crate(&mut self, span: Span, info: &ExternCrateInfo) -> ExtensionCrate {
@@ -614,7 +609,7 @@ impl<'a> CrateLoader<'a> {
              name: Symbol::intern(name),
              ident: Symbol::intern(name),
              id: ast::DUMMY_NODE_ID,
-             dep_kind: DepKind::MacrosOnly,
+             dep_kind: DepKind::UnexportedMacrosOnly,
         });
 
         if ekrate.target_only {
diff --git a/src/librustc_metadata/cstore.rs b/src/librustc_metadata/cstore.rs
index 7c1834c1576..73e03a45196 100644
--- a/src/librustc_metadata/cstore.rs
+++ b/src/librustc_metadata/cstore.rs
@@ -197,7 +197,7 @@ impl CStore {
             .borrow()
             .iter()
             .filter_map(|(&cnum, data)| {
-                if data.dep_kind.get() == DepKind::MacrosOnly { return None; }
+                if data.dep_kind.get().macros_only() { return None; }
                 let path = match prefer {
                     LinkagePreference::RequireDynamic => data.source.dylib.clone().map(|p| p.0),
                     LinkagePreference::RequireStatic => data.source.rlib.clone().map(|p| p.0),
diff --git a/src/librustc_metadata/cstore_impl.rs b/src/librustc_metadata/cstore_impl.rs
index ead933384b9..4b90d925972 100644
--- a/src/librustc_metadata/cstore_impl.rs
+++ b/src/librustc_metadata/cstore_impl.rs
@@ -228,6 +228,12 @@ impl<'tcx> CrateStore<'tcx> for cstore::CStore {
         self.get_crate_data(cnum).dep_kind.get()
     }
 
+    fn export_macros(&self, cnum: CrateNum) {
+        if self.get_crate_data(cnum).dep_kind.get() == DepKind::UnexportedMacrosOnly {
+            self.get_crate_data(cnum).dep_kind.set(DepKind::MacrosOnly)
+        }
+    }
+
     fn lang_items(&self, cnum: CrateNum) -> Vec<(DefIndex, usize)>
     {
         self.get_crate_data(cnum).get_lang_items()
diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index f59f2bcc074..d5b08927a06 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -21,7 +21,7 @@ use rustc::util::nodemap::FxHashMap;
 use rustc::hir;
 use rustc::hir::intravisit::IdRange;
 
-use rustc::middle::cstore::{DepKind, InlinedItem, LinkagePreference};
+use rustc::middle::cstore::{InlinedItem, LinkagePreference};
 use rustc::hir::def::{self, Def, CtorKind};
 use rustc::hir::def_id::{CrateNum, DefId, DefIndex, CRATE_DEF_INDEX, LOCAL_CRATE};
 use rustc::middle::lang_items;
@@ -729,7 +729,7 @@ impl<'a, 'tcx> CrateMetadata {
         };
 
         // Iterate over all children.
-        let macros_only = self.dep_kind.get() == DepKind::MacrosOnly;
+        let macros_only = self.dep_kind.get().macros_only();
         for child_index in item.children.decode(self) {
             if macros_only {
                 continue