fromJSON Crash With Bad Input

[brodieG]

On current CRAN version. Obviously shouldn't be a common issue, but this suggests there might be some undefined behavior lurking in the code that might be worth protecting against.

> rjson::fromJSON('"\\U1F600"')
R(9747,0x10fa46e00) malloc: *** error for object 0x7fba26f74370: pointer being freed was not allocated
R(9747,0x10fa46e00) malloc: *** set a breakpoint in malloc_error_break to debug
Abort trap: 6
rjson(issue20)$ 

R Under development (unstable) (2021-11-21 r81221)
Platform: x86_64-apple-darwin17.0 (64-bit)
Running under: macOS Big Sur/Monterey 10.16

Matrix products: default
BLAS:   /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRblas.0.dylib
LAPACK: /Library/Frameworks/R.framework/Versions/4.2/Resources/lib/libRlapack.dylib

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
 [1] compiler_4.2.0 R6_2.5.0       magrittr_2.0.1 tools_4.2.0    roxygen2_7.1.1
 [6] Rcpp_1.0.7     xml2_1.3.2     stringi_1.6.2  knitr_1.33     xfun_0.23     
[11] stringr_1.4.0  rlang_0.4.11   purrr_0.3.4  

[alexcb]

great catch -- there was a double free occurring in this case. fixed in 1775e6e