Eliminate `librustc_hir`'s dependency on `librustc_session`.

Cargo.lock

@@ -3466,7 +3466,6 @@ dependencies = [
  "rustc_index",
  "rustc_macros",
  "rustc_serialize",
- "rustc_session",
  "rustc_span",
  "rustc_target",
  "smallvec 1.4.0",

src/librustc_hir/Cargo.toml

@@ -16,7 +16,6 @@ rustc_data_structures = { path = "../librustc_data_structures" }
 rustc_index = { path = "../librustc_index" }
 rustc_span = { path = "../librustc_span" }
 rustc_serialize = { path = "../librustc_serialize" }
-rustc_session = { path = "../librustc_session" }
 rustc_ast = { path = "../librustc_ast" }
 lazy_static = "1"
 log = { package = "tracing", version = "0.1" }

src/librustc_hir/lang_items.rs

@@ -16,7 +16,6 @@
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
 use rustc_macros::HashStable_Generic;
-use rustc_session::Session;
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_span::Span;
 
@@ -142,12 +141,20 @@ fn hash_stable(&self, _: &mut CTX, hasher: &mut StableHasher) {
 /// Extracts the first `lang = "$name"` out of a list of attributes.
 /// The attributes `#[panic_handler]` and `#[alloc_error_handler]`
 /// are also extracted out when found.
-pub fn extract(sess: &Session, attrs: &[ast::Attribute]) -> Option<(Symbol, Span)> {
+///
+/// About the `check_name` argument: passing in a `Session` would be simpler,
+/// because then we could call `Session::check_name` directly. But we want to
+/// avoid the need for `librustc_hir` to depend on `librustc_session`, so we
+/// use a closure instead.
+pub fn extract<'a, F>(check_name: F, attrs: &'a [ast::Attribute]) -> Option<(Symbol, Span)>
+where
+    F: Fn(&'a ast::Attribute, Symbol) -> bool,
+{
     attrs.iter().find_map(|attr| {
         Some(match attr {
-            _ if sess.check_name(attr, sym::lang) => (attr.value_str()?, attr.span),
-            _ if sess.check_name(attr, sym::panic_handler) => (sym::panic_impl, attr.span),
-            _ if sess.check_name(attr, sym::alloc_error_handler) => (sym::oom, attr.span),
+            _ if check_name(attr, sym::lang) => (attr.value_str()?, attr.span),
+            _ if check_name(attr, sym::panic_handler) => (sym::panic_impl, attr.span),
+            _ if check_name(attr, sym::alloc_error_handler) => (sym::oom, attr.span),
             _ => return None,
         })
     })

src/librustc_hir/weak_lang_items.rs

@@ -5,7 +5,6 @@
 
 use rustc_ast::ast;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_session::Session;
 use rustc_span::symbol::{sym, Symbol};
 
 use lazy_static::lazy_static;
@@ -21,8 +20,13 @@
     };
 }
 
-pub fn link_name(sess: &Session, attrs: &[ast::Attribute]) -> Option<Symbol> {
-    lang_items::extract(sess, attrs).and_then(|(name, _)| {
+/// The `check_name` argument avoids the need for `librustc_hir` to depend on
+/// `librustc_session`.
+pub fn link_name<'a, F>(check_name: F, attrs: &'a [ast::Attribute]) -> Option<Symbol>
+where
+    F: Fn(&'a ast::Attribute, Symbol) -> bool
+{
+    lang_items::extract(check_name, attrs).and_then(|(name, _)| {
         $(if name == sym::$name {
             Some(sym::$sym)
         } else)* {

src/librustc_passes/lang_items.rs

@@ -56,7 +56,8 @@ fn new(tcx: TyCtxt<'tcx>) -> LanguageItemCollector<'tcx> {
     }
 
     fn check_for_lang(&mut self, actual_target: Target, hir_id: HirId, attrs: &[Attribute]) {
-        if let Some((value, span)) = extract(&self.tcx.sess, &attrs) {
+        let check_name = |attr, sym| self.tcx.sess.check_name(attr, sym);
+        if let Some((value, span)) = extract(check_name, &attrs) {
             match ITEM_REFS.get(&value).cloned() {
                 // Known lang item with attribute on correct target.
                 Some((item_index, expected_target)) if actual_target == expected_target => {

src/librustc_passes/weak_lang_items.rs

@@ -100,7 +100,8 @@ fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
     }
 
     fn visit_foreign_item(&mut self, i: &hir::ForeignItem<'_>) {
-        if let Some((lang_item, _)) = hir::lang_items::extract(&self.tcx.sess, &i.attrs) {
+        let check_name = |attr, sym| self.tcx.sess.check_name(attr, sym);
+        if let Some((lang_item, _)) = hir::lang_items::extract(check_name, &i.attrs) {
             self.register(lang_item, i.span, i.hir_id);
         }
         intravisit::walk_foreign_item(self, i)

src/librustc_typeck/collect.rs

@@ -2614,7 +2614,8 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, id: DefId) -> CodegenFnAttrs {
     if tcx.is_weak_lang_item(id) {
         codegen_fn_attrs.flags |= CodegenFnAttrFlags::RUSTC_STD_INTERNAL_SYMBOL;
     }
-    if let Some(name) = weak_lang_items::link_name(&tcx.sess, &attrs) {
+    let check_name = |attr, sym| tcx.sess.check_name(attr, sym);
+    if let Some(name) = weak_lang_items::link_name(check_name, &attrs) {
         codegen_fn_attrs.export_name = Some(name);
         codegen_fn_attrs.link_name = Some(name);
     }