Bug: operator precedence around **as** keyword is wrong

[ruabmbua]

Hi, I just tried the vscode plugin with the language server, and I had a great experience until now! Congrats for the great project!

About the bug:

I opened one of my projects, and immediately in my lib.rs I got a syntax error from the language server. I checked, if the error was valid by compiling the crate, but rustc does not issue any warnings or errors about this specific line of code.

Here is an example I created: playground.

You can try it on the playground, it compiles. If I run the following command with ra_cli, I get some syntax errors:

 > ra_cli parse < bug.rs | grep err
-------------------------------------
parsing: 237.974µs
                err: `expected COMMA`
                err: `expected SEMI`
          err: `expected SEMI`
          err: `expected expression`
  err: `expected an item`
  err: `expected an item`

The error seems to be only about line 7 in the example code. I think something about the + operator might mess up operator precedence, or something else in the parser. My second guess is, that the as u32 syntax is interpreted as something like as {TypeParamBounds}, and the + operator is part of the type / lifetime bounds for some reason. Link to the relevant section in the reference: Type expressions.

Update:
Found same parsing bug in one of the files in this repository: mock_analysis.rs#L76

[ruabmbua]

I think I found the bug.

the cast_expr function uses types::_type to get the type, into which the var should be casted.

This is suboptimal, because when type is an ident the function path_type() will be used to parse the type. This however calls path_type_(_, allow_bounds: bool) with true. It should directly call path_type_(_, false), to prevent the parser from eating the plus sign. Bounds are not allowed in the as expression according to language spec.

I will create a PR.

[DJMcNab]

Please see prior discussion in #273. I was waiting for @matklad to respond.