Combine std_inject::{no_core, no_std} into std_inject::injected_crate_name.

src/librustc/hir/lowering.rs

@@ -95,13 +95,7 @@ pub fn lower_crate(sess: &Session,
     let _ignore = sess.dep_graph.in_ignore();
 
     LoweringContext {
-        crate_root: if std_inject::no_core(krate) {
-            None
-        } else if std_inject::no_std(krate) {
-            Some("core")
-        } else {
-            Some("std")
-        },
+        crate_root: std_inject::injected_crate_name(krate),
         sess: sess,
         parent_def: None,
         resolver: resolver,

src/libsyntax/ext/base.rs

@@ -739,13 +739,7 @@ impl<'a> ExtCtxt<'a> {
     }
 
     pub fn initialize(&mut self, user_exts: Vec<NamedSyntaxExtension>, krate: &ast::Crate) {
-        if std_inject::no_core(&krate) {
-            self.crate_root = None;
-        } else if std_inject::no_std(&krate) {
-            self.crate_root = Some("core");
-        } else {
-            self.crate_root = Some("std");
-        }
+        self.crate_root = std_inject::injected_crate_name(krate);
 
         for (name, extension) in user_exts {
             let ident = ast::Ident::with_empty_ctxt(name);

src/libsyntax/print/pprust.rs

@@ -112,7 +112,7 @@ pub fn print_crate<'a>(cm: &'a CodeMap,
                                       out,
                                       ann,
                                       is_expanded);
-    if is_expanded && !std_inject::no_std(krate) {
+    if is_expanded && !std_inject::injected_crate_name(krate).is_none() {
         // We need to print `#![no_std]` (and its feature gate) so that
         // compiling pretty-printed source won't inject libstd again.
         // However we don't want these attributes in the AST because

src/libsyntax/std_inject.rs

@@ -34,23 +34,25 @@ fn ignored_span(sess: &ParseSess, sp: Span) -> Span {
     return sp;
 }
 
-pub fn no_core(krate: &ast::Crate) -> bool {
-    attr::contains_name(&krate.attrs, "no_core")
-}
-
-pub fn no_std(krate: &ast::Crate) -> bool {
-    attr::contains_name(&krate.attrs, "no_std") || no_core(krate)
+pub fn injected_crate_name(krate: &ast::Crate) -> Option<&'static str> {
+    if attr::contains_name(&krate.attrs, "no_core") {
+        None
+    } else if attr::contains_name(&krate.attrs, "no_std") {
+        Some("core")
+    } else {
+        Some("std")
+    }
 }
 
 pub fn maybe_inject_crates_ref(sess: &ParseSess,
                                mut krate: ast::Crate,
                                alt_std_name: Option<String>)
                                -> ast::Crate {
-    if no_core(&krate) {
-        return krate;
-    }
+    let name = match injected_crate_name(&krate) {
+        Some(name) => name,
+        None => return krate,
+    };
 
-    let name = if no_std(&krate) { "core" } else { "std" };
     let crate_name = token::intern(&alt_std_name.unwrap_or(name.to_string()));
 
     krate.module.items.insert(0, P(ast::Item {