Auto merge of #98187 - mystor:fast_span_call_site, r=eddyb

proc_macro/bridge: cache static spans in proc_macro's client thread-local state

This is the second part of https://github.com/rust-lang/rust/pull/86822, split off as requested in https://github.com/rust-lang/rust/pull/86822#pullrequestreview-1008655452. This patch removes the RPC calls required for the very common operations of `Span::call_site()`, `Span::def_site()` and `Span::mixed_site()`.

Some notes:

This part is one of the ones I don't love as a final solution from a design standpoint, because I don't like how the spans are serialized immediately at macro invocation. I think a more elegant solution might've been to reserve special IDs for `call_site`, `def_site`, and `mixed_site` at compile time (either starting at 1 or from `u32::MAX`) and making reading a Span handle automatically map these IDs to the relevant values, rather than doing extra serialization.

This would also have an advantage for potential future work to allow `proc_macro` to operate more independently from the compiler (e.g. to reduce the necessity of `proc-macro2`), as methods like `Span::call_site()` could be made to function without access to the compiler backend.

That was unfortunately tricky to do at the time, as this was the first part I wrote of the patches. After the later part (#98188, #98189), the other uses of `InternedStore` are removed meaning that a custom serialization strategy for `Span` is easier to implement.

If we want to go that path, we'll still need the majority of the work to split the bridge object and introduce the `Context` trait for free methods, and it will be easier to do after `Span` is the only user of `InternedStore` (after #98189).

compiler/rustc_expand/src/proc_macro_server.rs

@@ -14,7 +14,7 @@ use rustc_span::def_id::CrateNum;
 use rustc_span::symbol::{self, kw, sym, Symbol};
 use rustc_span::{BytePos, FileName, Pos, SourceFile, Span};
 
-use pm::bridge::{server, TokenTree};
+use pm::bridge::{server, ExpnGlobals, TokenTree};
 use pm::{Delimiter, Level, LineColumn, Spacing};
 use std::ops::Bound;
 use std::{ascii, panic};
@@ -370,7 +370,7 @@ impl<'a, 'b> Rustc<'a, 'b> {
     }
 
     fn lit(&mut self, kind: token::LitKind, symbol: Symbol, suffix: Option<Symbol>) -> Literal {
-        Literal { lit: token::Lit::new(kind, symbol, suffix), span: server::Span::call_site(self) }
+        Literal { lit: token::Lit::new(kind, symbol, suffix), span: self.call_site }
     }
 }
 
@@ -547,7 +547,7 @@ impl server::Group for Rustc<'_, '_> {
         Group {
             delimiter,
             stream: stream.unwrap_or_default(),
-            span: DelimSpan::from_single(server::Span::call_site(self)),
+            span: DelimSpan::from_single(self.call_site),
             flatten: false,
         }
     }
@@ -579,7 +579,7 @@ impl server::Group for Rustc<'_, '_> {
 
 impl server::Punct for Rustc<'_, '_> {
     fn new(&mut self, ch: char, spacing: Spacing) -> Self::Punct {
-        Punct::new(ch, spacing == Spacing::Joint, server::Span::call_site(self))
+        Punct::new(ch, spacing == Spacing::Joint, self.call_site)
     }
 
     fn as_char(&mut self, punct: Self::Punct) -> char {
@@ -829,18 +829,6 @@ impl server::Span for Rustc<'_, '_> {
         }
     }
 
-    fn def_site(&mut self) -> Self::Span {
-        self.def_site
-    }
-
-    fn call_site(&mut self) -> Self::Span {
-        self.call_site
-    }
-
-    fn mixed_site(&mut self) -> Self::Span {
-        self.mixed_site
-    }
-
     fn source_file(&mut self, span: Self::Span) -> Self::SourceFile {
         self.sess().source_map().lookup_char_pos(span.lo()).file
     }
@@ -926,3 +914,13 @@ impl server::Span for Rustc<'_, '_> {
         })
     }
 }
+
+impl server::Server for Rustc<'_, '_> {
+    fn globals(&mut self) -> ExpnGlobals<Self::Span> {
+        ExpnGlobals {
+            def_site: self.def_site,
+            call_site: self.call_site,
+            mixed_site: self.mixed_site,
+        }
+    }
+}