Error log not initialized when loading ~/.config/rebar3/rebar.config

[peterzeller]

When there is a syntax error in ~/.config/rebar3/rebar.config, rebar3 crashes before the log is initialized, so as a user I only see a stack trace pointing to the log function.

As an example, I had {plugins, [{rebar3_proper, 0.9.0}]}. in my config file (missed the quotes).

I could submit a pull request with a fallback to io:format if the log is not initialized.

Environment

• Add the result of rebar3 report to your message:

$ rebar3 report compile
escript: exception error: no match of right hand side value undefined
  in function  rebar_log:log/3 (/home/tristan/Devel/rebar3/_build/default/lib/rebar/src/rebar_log.erl, line 96)
  in call from rebar3:handle_error/1 (/home/tristan/Devel/rebar3/_build/default/lib/rebar/src/rebar3.erl, line 314)
  in call from escript:run/2 (escript.erl, line 757)
  in call from escript:start/1 (escript.erl, line 277)
  in call from init:start_em/1 
  in call from init:do_boot/3 

Without the crash (correct rebar.config)

$ rebar3 report compile
Rebar3 report
 version 3.5.0
 generated at 2018-05-28T16:27:11+00:00
=================
Please submit this along with your issue at https://github.com/erlang/rebar3/issues (and feel free to edit out private information, if any)
-----------------
Task: compile
Entered as:
  compile
-----------------
Operating System: x86_64-unknown-linux-gnu
ERTS: Erlang/OTP 19 [erts-8.1] [source] [64-bit] [smp:4:4] [async-threads:0] [hipe] [kernel-poll:false]
Root Directory: /home/peter/apps/erlang/19.1
Library directory: /home/peter/apps/erlang/19.1/lib
-----------------
Loaded Applications:
bbmustache: 1.3.0
certifi: 2.0.0
cf: 0.2.2
common_test: 1.12.3
compiler: 7.0.2
crypto: 3.7.1
cth_readable: 1.3.2
dialyzer: 3.0.2
edoc: 0.8
erlware_commons: 1.0.4
eunit: 2.3.1
eunit_formatters: 0.5.0
getopt: 1.0.1
inets: 6.3.3
kernel: 5.1
providers: 1.7.0
public_key: 1.2
relx: 3.24.3
sasl: 3.0.1
snmp: 5.2.4
ssl_verify_fun: 1.1.3
stdlib: 3.1
syntax_tools: 2.1
tools: 2.8.6

-----------------
Escript path: /home/peter/bin/rebar3
Providers:
  app_discovery as clean compile compile cover ct deps dialyzer do edoc escriptize eunit get-deps help install install_deps list lock new path pkgs proper release relup report shell state tar tree unlock update upgrade upgrade upgrade version xref 

[ferd]

That could be interesting. I don't see a big downside to it since it seems that it would at least allow the right error message to be output.

Maybe the io:format should mention something like io:format("fallback log: ~ts~n", [Str]) so we can at least find where things have been going wrong