add null check for module-default-defs

[ssikdar1]

Description

Issue #34544.
In PR #35337 there was a suggestion to add a check for body in module-default-defs in src/jlfrontend.scm. This adds that check.

Testing

In the julia repl I tried a couple more variations that would cause a segfault

julia> eval(Expr(:call, :eval, Expr(:quote, Expr(:module, true, :bar, Expr(:block)))))
Main.bar

julia> eval(Expr(:module, true, :bar, Expr(:block)))
WARNING: replacing module bar.
Main.bar

julia> eval(Expr(:module, true, :bar, Expr(:quote)))
WARNING: replacing module bar.
Main.bar

julia> eval(Expr(:call, :eval, Expr(:quote, Expr(:module, true, :bar, Expr(:block)))))
WARNING: replacing module bar.
Main.bar

[JeffBezanson]

Great, thanks! Could you add a test case to test/syntax.jl?

[ssikdar1]

5a0b565 adds a fix for #35367 as well

Output for those two lines in the REPL:

$ ./julia 
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.5.0-DEV.572 (2020-04-06)
 _/ |\__'_|_|_|\__'_|  |  linenumber/0b9ed994df* (fork: 2 commits, 4 days)
|__/                   |

julia> eval(Expr(:quote, Expr(:module, true, :bar, Expr(:quote))))
:(module bar
  end)

julia> eval(Expr(:call, :eval, Expr(:quote, Expr(:module, true, :bar, Expr(:quote)))))
Main.bar

[JeffBezanson]

iscons(e) needs to be checked before car_(e); car is only valid if e is a cons.

[JeffBezanson]

I don't think this should be valid; the 3rd argument to module has to be a block expression. That can be checked at the top of jl_eval_module_expr.

[ssikdar1]

@JeffBezanson added an if check inside jl_eval_module_expr in dce7897.

The following now throw an Exception:

julia> eval(Expr(:call, :eval, Expr(:quote, Expr(:module, true, :bar, Expr(:quote)))))
ERROR: syntax: module expression third argument must be a block

julia> eval(Expr(:module, true, :bar, Expr(:foo)))
ERROR: syntax: module expression third argument must be a block

julia> eval(Expr(:module, true, :bar, Expr(:quote)))
ERROR: syntax: module expression third argument must be a block

The following does not return an ErrorException (but no longer segfaults ):

julia> eval(Expr(:quote, Expr(:module, true, :bar, Expr(:quote))))
:(module bar
  end)

I think due to the quoting? Which I think is fine?

[mbauman]

I just hit this bug myself — glad to see a fix already here! My use-case was a macro:

julia> macro foo()
           Expr(:module, true, esc(:Bar), Expr(:block))
       end
@foo (macro with 1 method)

julia> @foo
WARNING: replacing module Bar.

signal (11): Segmentation fault: 11

[JeffBezanson]

I think due to the quoting? Which I think is fine?

Right; the eval just strips off the quote, so the module expression itself is never evaluated, so the error doesn't happen.