Merge #4105

4105: Adds attribute completions (#3941) r=matklad a=jrvidal

I've hacked together some basic completions for a few builtin attributes.

* I have no idea what `CompletionItemKind` we should set for them.
* There's plenty of fancy stuff we could do by detecting the item the attribute is being added to. Nothing of that here.
* Maybe we could complete as soon as you type `#` or `#!`?

I'm not sure what info exactly we can dump on `CompletionContext` and what we should query during the completion calculation itself. I've assumed adding an `is_attribute` field is OK, since it allows to discard the completion quickly if it doesn't apply. Later we inspect the AST to find out whether it is an inner attribute or not.

Co-authored-by: Roberto Vidal <[email protected]>

Author: bors[bot]

crates/ra_ide/src/completion.rs

@@ -5,6 +5,7 @@ mod completion_item;
 mod completion_context;
 mod presentation;
 
+mod complete_attribute;
 mod complete_dot;
 mod complete_record;
 mod complete_pattern;
@@ -78,6 +79,7 @@ pub(crate) fn completions(
     complete_postfix::complete_postfix(&mut acc, &ctx);
     complete_macro_in_item_position::complete_macro_in_item_position(&mut acc, &ctx);
     complete_trait_impl::complete_trait_impl(&mut acc, &ctx);
+    complete_attribute::complete_attribute(&mut acc, &ctx);
 
     Some(acc)
 }