rustdoc: Remove `Crate.src` and instead compute it on-demand

It is only used in one place; `src` was about a third of `Crate`'s total
size; `Crate` is frequently moved by-value; and `src` can be easily
computed on-demand.

src/librustdoc/clean/types.rs

@@ -117,7 +117,6 @@ fn from(id: DefId) -> Self {
 #[derive(Clone, Debug)]
 crate struct Crate {
     crate name: Symbol,
-    crate src: FileName,
     crate module: Item,
     crate externs: Vec<ExternalCrate>,
     crate primitives: ThinVec<(DefId, PrimitiveType)>,
@@ -128,7 +127,13 @@ fn from(id: DefId) -> Self {
 
 // `Crate` is frequently moved by-value. Make sure it doesn't unintentionally get bigger.
 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
-rustc_data_structures::static_assert_size!(Crate, 168);
+rustc_data_structures::static_assert_size!(Crate, 104);
+
+impl Crate {
+    crate fn src(&self, tcx: TyCtxt<'_>) -> FileName {
+        ExternalCrate::LOCAL.src(tcx)
+    }
+}
 
 /// This struct is used to wrap additional information added by rustdoc on a `trait` item.
 #[derive(Clone, Debug)]

src/librustdoc/clean/utils.rs

@@ -57,7 +57,6 @@
     }
 
     let local_crate = ExternalCrate { crate_num: LOCAL_CRATE };
-    let src = local_crate.src(cx.tcx);
     let name = local_crate.name(cx.tcx);
     let primitives = local_crate.primitives(cx.tcx);
     let keywords = local_crate.keywords(cx.tcx);
@@ -81,7 +80,6 @@
 
     Crate {
         name,
-        src,
         module,
         externs,
         primitives,

src/librustdoc/html/render/context.rs

@@ -405,7 +405,7 @@ fn init(
             ..
         } = options;
 
-        let src_root = match krate.src {
+        let src_root = match krate.src(tcx) {
             FileName::Real(ref p) => match p.local_path_if_available().parent() {
                 Some(p) => p.to_path_buf(),
                 None => PathBuf::new(),