Compiler hang when importing big JS file with --allowJs

[pjmolina]

TypeScript Version: 2.4.1

Repro project
When importing a big JS file (a working parser) (245 Kbytes commonjs format) (with --allowJs enabled) the compiler hangs forever. Minimal repro project provided: tsc-hang-00

Expected behavior:
Compilations ends with or without errors.

Actual behavior:
Compilations hangs forever and keeps consuming CPU.

Tests conditions

• Windows 10, NodeJS 8.0, TS 2.4.1
• Travis: Linux Container, NodeJS 8.0, TS 2.4.1

[filipesilva]

I tried to profile what's going on here and trying to capture a CPU profile for any length of time (even 1s) will cause the Chrome profiler to crash while processing the CPU profile.

[sandersn]

Profiling probably isn't useful for a 245k file — it's usually a bug or an algorithmic performance problem, both of which usually express themselves as very deep stacks. My initial debugging method is to start debugging and just pause a few times. I'll fall back to profiling (or printf debugging of caches) if there doesn't seem to be a pattern in the locations.

There are two relevant meanings of 'location': which node is currently being checked, and where the instruction pointer is when debugging is paused.