Global scoped try/catch emits compilation error

[Ferossgp]

I've been trying to compile an app bundle generated by Closure Compiler.

Compiling the bundle with the Hermes compiler:

hermesc -O -emit-binary -out ./test.hbc /test.js

emits the following error:

index.js:1:1: error: Too deeply nested try/catch

Hermes versions tested with:

LLVM (http://llvm.org/):
  LLVH version 8.0.0svn
  Optimized build

Hermes JavaScript compiler.
  Hermes release version: 0.7.2
  HBC bytecode version: 76

  Features:
    Debugger
    Zip file input
---------------------------------
LLVM (http://llvm.org/):
  LLVH version 8.0.0svn
  Optimized build

Hermes JavaScript compiler.
  Hermes release version: 0.8.0
  HBC bytecode version: 83

  Features:
    Debugger
    Zip file input

By inspecting the JS code I found that the reason is the presence of a try/catch in the global scope. The try/catch does not have any recursion and deep function traces inside its scope. Removing it solves the error.

Adding this try {} catch (a) {} at the end of file, also causes the error.

Seems like there is something else in the bundle that in combination with a global try/catch causes the error.

In a simple test project, the error is not reproducible. I want to create a repro thus I would like to know some hints for the direction to dig in.

[avp]

You can perhaps try deleting pieces of the code in order to figure out which parts are actually making things fail.

If you build Hermes with debug information (https://github.com/facebook/hermes/blob/master/doc/BuildingAndRunning.md) then you can also attach a debugger and breakpoint on the error message (it's in lib/BCGen/Exceptions.cpp) in order to look at the stacktrace and perhaps help figure out how you can find a useful repro we can take a look at.

[Ferossgp]

@avp Thank you!

There is a gist that throws the same exception https://gist.github.com/Ferossgp/c4107f30bb686f56c5f2893541838eda

I will try to create a reproduction without so many try/catch'es too. Basically what I've found is that this code:

try{} catch(a){}

function recursive(argument) {
  if (argument) {
    recursive(argument--)
  }
}

also decreases the maxRecursionDepth inside the lib/BCGen/Exceptions.cpp, and by removing the try-catch does not execute that part of the code anymore.

[avp]

Thanks for the reproduction. We'll take a look and see what has to be done to avoid hitting this case in the wrong circumstances.

[neildhar]

@Ferossgp This should be fixed in 42f8319, are you able to build Hermes from trunk and verify that the issue with your bundle is resolved?

[Ferossgp]

@neildhar yes, thank you! Can confirm that the build from 42f8319 solved the issue for us.

[neildhar]

Great, thanks for confirming!