Small cleanups

- Use a tuple struct instead of a single field
- Enforce calling `source_callsite()` by making the inner span private
- Rename `empty` to `dummy`

Author: jyn514

Diff for: src/librustdoc/clean/auto_trait.rs

@@ -118,7 +118,7 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
                 };
 
                 Some(Item {
-                    source: Span::empty(),
+                    source: Span::dummy(),
                     name: None,
                     attrs: Default::default(),
                     visibility: Inherited,

Diff for: src/librustdoc/clean/inline.rs

@@ -479,7 +479,7 @@ fn build_module(cx: &DocContext<'_>, did: DefId, visited: &mut FxHashSet<DefId>)
                     items.push(clean::Item {
                         name: None,
                         attrs: clean::Attributes::default(),
-                        source: clean::Span::empty(),
+                        source: clean::Span::dummy(),
                         def_id: DefId::local(CRATE_DEF_INDEX),
                         visibility: clean::Public,
                         stability: None,

Diff for: src/librustdoc/clean/mod.rs

@@ -1882,10 +1882,7 @@ impl Clean<VariantKind> for hir::VariantData<'_> {
 
 impl Clean<Span> for rustc_span::Span {
     fn clean(&self, _cx: &DocContext<'_>) -> Span {
-        // Get the macro invocation instead of the definition,
-        // in case the span is result of a macro expansion.
-        // (See rust-lang/rust#39726)
-        Span { original: self.source_callsite() }
+        Span::from_rustc_span(*self)
     }
 }
 

Diff for: src/librustdoc/clean/types.rs

@@ -1610,31 +1610,36 @@ crate enum VariantKind {
     Struct(VariantStruct),
 }
 
-/// Small wrapper around `rustc_span::Span` that adds helper methods.
+/// Small wrapper around `rustc_span::Span` that adds helper methods and enforces calling `source_callsite`.
 #[derive(Clone, Debug)]
-crate struct Span {
-    crate original: rustc_span::Span,
-}
+crate struct Span(rustc_span::Span);
 
 impl Span {
-    crate fn empty() -> Self {
-        Self { original: rustc_span::DUMMY_SP }
+    crate fn from_rustc_span(sp: rustc_span::Span) -> Self {
+        // Get the macro invocation instead of the definition,
+        // in case the span is result of a macro expansion.
+        // (See rust-lang/rust#39726)
+        Self(sp.source_callsite())
+    }
+
+    crate fn dummy() -> Self {
+        Self(rustc_span::DUMMY_SP)
     }
 
     crate fn span(&self) -> rustc_span::Span {
-        self.original
+        self.0
     }
 
     crate fn filename(&self, sess: &Session) -> FileName {
-        sess.source_map().span_to_filename(self.original)
+        sess.source_map().span_to_filename(self.0)
     }
 
     crate fn lo(&self, sess: &Session) -> Loc {
-        sess.source_map().lookup_char_pos(self.original.lo())
+        sess.source_map().lookup_char_pos(self.0.lo())
     }
 
     crate fn hi(&self, sess: &Session) -> Loc {
-        sess.source_map().lookup_char_pos(self.original.hi())
+        sess.source_map().lookup_char_pos(self.0.hi())
     }
 
     crate fn cnum(&self, sess: &Session) -> CrateNum {