assert! allows invalid trailing tokens in expression

[adlerd]

fn main() {
    assert!(true some extra junk, "whatever");  
    assert!(true some extra junk);                    
}

(Playground)

Output:

   Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 0.54s
     Running `target/debug/playground`

Version:

• 1.34.0
• 1.35.0 2019-04-15 nightly (2975a3c)

Expected:

error: expected one of `.`, `;`, `?`, or an operator, found `some`
 --> src/main.rs:2:18
  |
2 |     assert!(true some extra junk, "whatever");
  |                  ^^^^ expected one of `.`, `;`, `?`, or an operator here

Original report:
https://www.reddit.com/r/rust/comments/bdbtpr/hey_rustaceans_got_an_easy_question_ask_here/el1gm0h/

[jonas-schievink]

1.26.0 is the first version that accepts this. 1.25.0 rejects it with:

error: no rules expected the token `some`
 --> test.rs:2:18
  |
2 |     assert!(true some extra junk, "whatever");  
  |                  ^^^^

error: no rules expected the token `some`
 --> test.rs:3:18
  |
3 |     assert!(true some extra junk);                    
  |                  ^^^^

error: aborting due to 2 previous errors

[jonas-schievink]

(not really a regression since more code now compiles)

[Centril]

Adding T-compiler since assert! is a built-in.

[rasendubi]

Opened #60039—it should fix the issue.

[pnkfelix]

triage: P-medium. I'm going to assume we don't need any future-compat machinery for a bug of this nature, unless the crater run on PR #60039 indicates that there are occurrences of this mis-use of assert! in the wild.