Angle bracket (>) seems to cause 100% cpu.

[jmb1026]

Problem

While following along with this tutorial ng2-ts mode seems to cause emacs to block and use 100% of the CPU. The code in question is from the "Error handling" section, specifically:

private handleError<T> (operation = 'operation', result?: T) {
  return (error: any): Observable<T> => {  // Typing the second > on this line causes the issue.
     // ...
  };
}

Environment

• MacOS 10.14.6
• iTerm2 Build 3.3.7
• Angular CLI: 8.3.20
• Node: 12.13.1
• Angular: 8.2.14
• Emacs 26.3

Emacs configuration

 ;; Angular/Typescript
 (use-package typescript-mode
    :ensure t)

 (use-package ng2-mode
    :ensure t
    :after typescript-mode)

Steps to reproduce

1. ng new repro Accept defaults.
2. cd repro
3. Launch emacs and open repro/src/app/app.module.ts
4. In the AppModule class, add the following block

getRepro() {
  return (): <T> => {
  }
}

5. Typing the second gt bracket (>) will reproduce the issue.

Misc.

• The issue does not happen with only typescript-mode enabled.
• Once the offending block of code is in the file, emacs will hang when attempting to open the file.
• Emacs does not recover. SIGKILL is the only option.

[LlinksRechts]

Any updates on this? What I have found out:

• this seems to only be a problem for generics in return types in lambdas
• it seems to be an issue with syntax highlighting; SIGUSR2 can throw emacs out of the loop, which prints the following stack trace:

  * #f(compiled-function () #<bytecode 0x166b8e1>)()    
  ng2-ts--inside-lambda-args-p(119)                   
  ng2-ts--highlight-lambda-args-fn(131)               
  font-lock-fontify-keywords-region(1 131 nil)        
  font-lock-default-fontify-region(1 131 nil)         

• The problem does not occur with brackets around the problematic type, ie. instead of (): Promise<void> => {}, use (): (Promise<void>) => {} (-> temporary fix)

[LlinksRechts]

For anyone else running into this issue: I fixed it using

--- a/ng2-ts.el
+++ b/ng2-ts.el
@@ -198,6 +198,7 @@
                            (min bound (ng2-ts--end-of-lambda-args (point))) 1))
       (and (ignore-errors
              ;; Skip forward if we wind up in the space between the args and the =>
+             (save-match-data (while (looking-at ">") (forward-char)))
              (ng2-ts--skip-whitespace)
              (forward-char 2)
              (prog1 (save-match-data (search-forward "=>" bound 1))

However that is relatively hacky and I really don't know elisp, so I'm not submitting a PR :p

[AdamNiederer]

Oh, hey!

Honestly syntax highlighting in emacs is a massive hack anyway. If this fixes it, shoot me an PR and I'll put it in. Rather some edge case not get highlighted than have your editor hang.