.mll tests fail when running `./scripts/ninja.js build`

[kevinbarabash]

I get the following output when running ./scripts/ninja.js build (after running the other steps in CONTRIBUTING.md):

./scripts/ninja.js build
rescript: [91/1832] stubs/libbs_hash.a
+ cc -shared -flat_namespace -undefined suppress                    -Wl,-no_compact_unwind  -o stubs/dllbs_hash.so stubs/ext_basic_hash_stubs.o     
+ ar rc stubs/libbs_hash.a  stubs/ext_basic_hash_stubs.o; ranlib stubs/libbs_hash.a
rescript: [830/1832] test/arith_lexer.ml
FAILED: test/arith_lexer.ml
/bin/sh: test/arith_lexer.mll: Permission denied
rescript: [831/1832] test/number_lexer.ml
FAILED: test/number_lexer.ml
/bin/sh: test/number_lexer.mll: Permission denied
rescript: [834/1832] test/simple_lexer_test.ml
FAILED: test/simple_lexer_test.ml
/bin/sh: test/simple_lexer_test.mll: Permission denied
rescript: [1828/1832] test/unsafe_this.cmj
FAILED: cannot make progress due to previous errors.
Command failed: /Users/kevinbarabash/projects/rescript-compiler/darwin/ninja.exe native all
please run "./scripts/ninja.js config" first

The contents of jscomp/build.ninja is

subninja compiler.ninja
stdlib = stdlib-406
bsc = ../darwin/bsc.exe
subninja runtime/build.ninja
subninja others/build.ninja
subninja $stdlib/build.ninja
subninja test/build.ninja
o all: phony runtime others $stdlib test

which means that $ocamllex in jscomp/test/build.ninja is undefined. As a result when rule mll that makes use of $ocamllex tries to run, it instead ends up trying to execute the .mll files instead of running ocamllex.

rule mll
    command = $ocamllex $in
    generator = true

o test/arith_lexer.ml : mll test/arith_lexer.mll
o test/number_lexer.ml : mll test/number_lexer.mll
o test/simple_lexer_test.ml : mll test/simple_lexer_test.mll

I was able to fix this by updating ninja.js to include a line in jscomp/build.ninja that sets:

ocamllex = ocamllex.opt

I'm not familiar with the ninja build system so I'm not sure if this is the right fix. If it is, let me know and I can submit a PR with my change.