Address comments

Author: petrochenkov

Diff for: src/libproc_macro/lib.rs

@@ -1434,9 +1434,12 @@ pub mod __internal {
         CURRENT_SESS.with(|p| {
             let _reset = Reset { prev: p.get() };
 
-            // No way to determine def location for a proc macro rigth now, so use call location.
+            // No way to determine def location for a proc macro right now, so use call location.
             let location = cx.current_expansion.mark.expn_info().unwrap().call_site;
             // Opaque mark was already created by expansion, now create its transparent twin.
+            // We can't use the call-site span literally here, even if it appears to provide
+            // correct name resolution, because it has all the `ExpnInfo` wrong, so the edition
+            // checks, lint macro checks, macro backtraces will all break.
             let opaque_mark = cx.current_expansion.mark;
             let transparent_mark = Mark::fresh_cloned(opaque_mark);
             transparent_mark.set_transparency(Transparency::Transparent);

Diff for: src/librustc_resolve/lib.rs

@@ -2005,10 +2005,9 @@ impl<'a> Resolver<'a> {
                 }
             }
             // Then find the last legacy mark from the end if it exists.
-            while let Some(&mark) = iter.peek() {
+            for mark in iter {
                 if mark.transparency() == Transparency::SemiTransparent {
                     result = Some(mark);
-                    iter.next();
                 } else {
                     break;
                 }

Diff for: src/libsyntax_pos/hygiene.rs

@@ -57,7 +57,6 @@ struct MarkData {
 pub enum Transparency {
     /// Identifier produced by a transparent expansion is always resolved at call-site.
     /// Call-site spans in procedural macros, hygiene opt-out in `macro` should use this.
-    /// (Not used yet.)
     Transparent,
     /// Identifier produced by a semi-transparent expansion may be resolved
     /// either at call-site or at definition-site.

Diff for: src/libsyntax_pos/symbol.rs

@@ -68,11 +68,11 @@ impl Ident {
         Ident::new(self.name, self.span.modern())
     }
 
-    // "Normalize" ident for use in comparisons using "local variable hygiene".
-    // Identifiers with same string value become same if they came from the same non-transparent
-    // macro (e.g. `macro` or `macro_rules!` items) and stay different if they came from different
-    // non-transparent macros.
-    // Technically, this operation strips all transparent marks from ident's syntactic context.
+    /// "Normalize" ident for use in comparisons using "local variable hygiene".
+    /// Identifiers with same string value become same if they came from the same non-transparent
+    /// macro (e.g. `macro` or `macro_rules!` items) and stay different if they came from different
+    /// non-transparent macros.
+    /// Technically, this operation strips all transparent marks from ident's syntactic context.
     pub fn modern_and_legacy(self) -> Ident {
         Ident::new(self.name, self.span.modern_and_legacy())
     }