[perf] rustdoc: Don't obtain early resolver unless --generate-macro-expansion

Author: fmease

src/librustdoc/core.rs

@@ -340,13 +340,7 @@ pub(crate) fn run_global_ctxt(
     // (see https://github.com/rust-lang/rust/pull/73566#issuecomment-656954425),
     // so type-check everything other than function bodies in this crate before running lints.
 
-    let expanded_macros = {
-        // We need for these variables to be removed to ensure that the `Crate` won't be "stolen"
-        // anymore.
-        let (_resolver, krate) = &*tcx.resolver_for_lowering().borrow();
-
-        source_macro_expansion(&krate, &render_options, output_format, tcx.sess.source_map())
-    };
+    let expanded_macros = source_macro_expansion(&render_options, output_format, tcx);
 
     // NOTE: this does not call `tcx.analysis()` so that we won't
     // typeck function bodies or run the default rustc lints.

src/librustdoc/html/macro_expansion.rs

@@ -1,22 +1,27 @@
 use rustc_ast::visit::{Visitor, walk_crate, walk_expr, walk_item, walk_pat, walk_stmt};
-use rustc_ast::{Crate, Expr, Item, Pat, Stmt};
+use rustc_ast::{Expr, Item, Pat, Stmt};
 use rustc_data_structures::fx::FxHashMap;
+use rustc_middle::ty::TyCtxt;
 use rustc_span::source_map::SourceMap;
 use rustc_span::{BytePos, Span};
 
 use crate::config::{OutputFormat, RenderOptions};
 
 /// It returns the expanded macros correspondence map.
 pub(crate) fn source_macro_expansion(
-    krate: &Crate,
     render_options: &RenderOptions,
     output_format: OutputFormat,
-    source_map: &SourceMap,
+    tcx: TyCtxt<'_>,
 ) -> FxHashMap<BytePos, Vec<ExpandedCode>> {
-    if output_format == OutputFormat::Html
+    if render_options.generate_macro_expansion
+        && output_format == OutputFormat::Html
         && !render_options.html_no_source
-        && render_options.generate_macro_expansion
     {
+        // We need for these variables to be removed to ensure that the `Crate` won't be "stolen"
+        // anymore.
+        let (_resolver, krate) = &*tcx.resolver_for_lowering().borrow();
+        let source_map = tcx.sess.source_map();
+
         let mut expanded_visitor = ExpandedCodeVisitor { expanded_codes: Vec::new(), source_map };
         walk_crate(&mut expanded_visitor, krate);
         expanded_visitor.compute_expanded()