Auto merge of #57792 - Centril:rollup, r=Centril

Rollup of 5 pull requests

Successful merges:

 - #56796 (Change bounds on `TryFrom` blanket impl to use `Into` instead of `From`)
 - #57768 (Continue parsing after parent type args and suggest using angle brackets)
 - #57769 (Suggest correct cast for struct fields with shorthand syntax)
 - #57783 (Add "dereference boxed value" suggestion.)
 - #57784 (Add span for bad doc comment)

Failed merges:

r? @ghost

2 files changed, 19 insertions, 5 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index f411e40e160..405cf612543 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -192,6 +192,16 @@ pub struct ParenthesisedArgs {
     pub output: Option<P<Ty>>,
 }
 
+impl ParenthesisedArgs {
+    pub fn as_angle_bracketed_args(&self) -> AngleBracketedArgs {
+        AngleBracketedArgs {
+            span: self.span,
+            args: self.inputs.iter().cloned().map(|input| GenericArg::Type(input)).collect(),
+            bindings: vec![],
+        }
+    }
+}
+
 // hack to ensure that we don't try to access the private parts of `NodeId` in this module
 mod node_id_inner {
     use rustc_data_structures::indexed_vec::Idx;
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 7e15b231276..439eec5b0c4 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -2176,11 +2176,11 @@ impl<'a> Parser<'a> {
               style != PathStyle::Mod && self.check(&token::ModSep)
                                       && self.look_ahead(1, |t| is_args_start(t)) {
             // Generic arguments are found - `<`, `(`, `::<` or `::(`.
-            let lo = self.span;
             if self.eat(&token::ModSep) && style == PathStyle::Type && enable_warning {
                 self.diagnostic().struct_span_warn(self.prev_span, "unnecessary path disambiguator")
                                  .span_label(self.prev_span, "try removing `::`").emit();
             }
+            let lo = self.span;
 
             let args = if self.eat_lt() {
                 // `<'a, T, A = U>`
@@ -4483,13 +4483,17 @@ impl<'a> Parser<'a> {
     }
 
     /// Emit an expected item after attributes error.
-    fn expected_item_err(&self, attrs: &[Attribute]) {
+    fn expected_item_err(&mut self, attrs: &[Attribute]) -> PResult<'a,  ()> {
         let message = match attrs.last() {
             Some(&Attribute { is_sugared_doc: true, .. }) => "expected item after doc comment",
             _ => "expected item after attributes",
         };
 
-        self.span_err(self.prev_span, message);
+        let mut err = self.diagnostic().struct_span_err(self.prev_span, message);
+        if attrs.last().unwrap().is_sugared_doc {
+            err.span_label(self.prev_span, "this doc comment doesn't document anything");
+        }
+        Err(err)
     }
 
     /// Parse a statement. This stops just before trailing semicolons on everything but items.
@@ -7636,7 +7640,7 @@ impl<'a> Parser<'a> {
             }
             None => {
                 if !attrs.is_empty()  {
-                    self.expected_item_err(&attrs);
+                    self.expected_item_err(&attrs)?;
                 }
 
                 self.unexpected()
@@ -7699,7 +7703,7 @@ impl<'a> Parser<'a> {
         }
 
         if !attributes_allowed && !attrs.is_empty() {
-            self.expected_item_err(&attrs);
+            self.expected_item_err(&attrs)?;
         }
         Ok(None)
     }