Use a symbol for ExpansionConfig::crate_name.

This avoids some symbol interning and `to_string` conversions.

compiler/rustc_builtin_macros/src/proc_macro_harness.rs

@@ -56,7 +56,7 @@ pub fn inject(
     is_test_crate: bool,
     dcx: DiagCtxtHandle<'_>,
 ) {
-    let ecfg = ExpansionConfig::default("proc_macro".to_string(), features);
+    let ecfg = ExpansionConfig::default(sym::proc_macro, features);
     let mut cx = ExtCtxt::new(sess, ecfg, resolver, None);
 
     let mut collect = CollectProcMacros {

compiler/rustc_builtin_macros/src/standard_library_imports.rs

@@ -36,7 +36,7 @@ pub fn inject(
     let span = DUMMY_SP.with_def_site_ctxt(expn_id.to_expn_id());
     let call_site = DUMMY_SP.with_call_site_ctxt(expn_id.to_expn_id());
 
-    let ecfg = ExpansionConfig::default("std_lib_injection".to_string(), features);
+    let ecfg = ExpansionConfig::default(sym::std_lib_injection, features);
     let cx = ExtCtxt::new(sess, ecfg, resolver, None);
 
     let ident_span = if edition >= Edition2018 { span } else { call_site };

compiler/rustc_builtin_macros/src/test_harness.rs

@@ -227,7 +227,7 @@ fn generate_test_harness(
     panic_strategy: PanicStrategy,
     test_runner: Option<ast::Path>,
 ) {
-    let econfig = ExpansionConfig::default("test".to_string(), features);
+    let econfig = ExpansionConfig::default(sym::test, features);
     let ext_cx = ExtCtxt::new(sess, econfig, resolver, None);
 
     let expn_id = ext_cx.resolver.expansion_for_ast_pass(

compiler/rustc_expand/src/errors.rs

@@ -183,12 +183,12 @@ pub(crate) struct FeatureNotAllowed {
 #[derive(Diagnostic)]
 #[diag(expand_recursion_limit_reached)]
 #[help]
-pub(crate) struct RecursionLimitReached<'a> {
+pub(crate) struct RecursionLimitReached {
     #[primary_span]
     pub span: Span,
     pub descr: String,
     pub suggested_limit: Limit,
-    pub crate_name: &'a str,
+    pub crate_name: Symbol,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_expand/src/expand.rs

@@ -26,7 +26,7 @@ use rustc_session::lint::builtin::{UNUSED_ATTRIBUTES, UNUSED_DOC_COMMENTS};
 use rustc_session::parse::feature_err;
 use rustc_session::{Limit, Session};
 use rustc_span::hygiene::SyntaxContext;
-use rustc_span::{ErrorGuaranteed, FileName, Ident, LocalExpnId, Span, sym};
+use rustc_span::{ErrorGuaranteed, FileName, Ident, LocalExpnId, Span, Symbol, sym};
 use smallvec::SmallVec;
 
 use crate::base::*;
@@ -473,7 +473,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
         let dir_path = file_path.parent().unwrap_or(&file_path).to_owned();
         self.cx.root_path = dir_path.clone();
         self.cx.current_expansion.module = Rc::new(ModuleData {
-            mod_path: vec![Ident::from_str(&self.cx.ecfg.crate_name)],
+            mod_path: vec![Ident::with_dummy_span(self.cx.ecfg.crate_name)],
             file_path_stack: vec![file_path],
             dir_path,
         });
@@ -689,7 +689,7 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
             span: expn_data.call_site,
             descr: expn_data.kind.descr(),
             suggested_limit,
-            crate_name: &self.cx.ecfg.crate_name,
+            crate_name: self.cx.ecfg.crate_name,
         });
 
         self.cx.trace_macros_diag();
@@ -2458,7 +2458,7 @@ impl<'a, 'b> MutVisitor for InvocationCollector<'a, 'b> {
 }
 
 pub struct ExpansionConfig<'feat> {
-    pub crate_name: String,
+    pub crate_name: Symbol,
     pub features: &'feat Features,
     pub recursion_limit: Limit,
     pub trace_mac: bool,
@@ -2471,7 +2471,7 @@ pub struct ExpansionConfig<'feat> {
 }
 
 impl ExpansionConfig<'_> {
-    pub fn default(crate_name: String, features: &Features) -> ExpansionConfig<'_> {
+    pub fn default(crate_name: Symbol, features: &Features) -> ExpansionConfig<'_> {
         ExpansionConfig {
             crate_name,
             features,

compiler/rustc_interface/src/passes.rs

@@ -192,7 +192,7 @@ fn configure_and_expand(
         // Create the config for macro expansion
         let recursion_limit = get_recursion_limit(pre_configured_attrs, sess);
         let cfg = rustc_expand::expand::ExpansionConfig {
-            crate_name: crate_name.to_string(),
+            crate_name,
             features,
             recursion_limit,
             trace_mac: sess.opts.unstable_opts.trace_macros,

compiler/rustc_span/src/symbol.rs

@@ -2052,6 +2052,7 @@ symbols! {
         static_recursion,
         staticlib,
         std,
+        std_lib_injection,
         std_panic,
         std_panic_2015_macro,
         std_panic_macro,