[patch] use proper error reporting for toplevel's environment initialization

[vicuna]

Original bug ID: 6401
Reporter: @gasche
Assigned to: @alainfrisch
Status: closed (set by @xavierleroy on 2017-02-16T14:16:19Z)
Resolution: fixed
Priority: low
Severity: feature
Target version: 4.03.0+dev / +beta1
Fixed in version: 4.03.0+dev / +beta1
Category: tools (ocaml{lex,yacc,dep,debug,...})
Tags: patch
Monitored by: @hcarty

Bug description

When hacking on the compiler itself, a classic failure when running the toplevel is that it tries to link against the installed standard library instead of the one being modified, which gives various interface mismatches -- the fix is to pass "-I stdlib -nostdlib", and I also need "-noinit" for other reasons.

On trunk, the reporting is currently not very nice (there might be a regression from older versions):

% ./byterun/ocamlrun ./ocaml
OCaml version 4.02.0+dev5-2014-04-29

Fatal error: exception Env.Error(_)

The attached patch calls the error-reporting routines to print a better error message:

% ./byterun/ocamlrun ./ocaml
OCaml version 4.02.0+dev5-2014-04-29

File "none", line 1:
Error: The files ./ocaml
and /home/gabriel/.opam/4.02.0local+git-trunk/lib/ocaml/pervasives.cmi
make inconsistent assumptions over interface Pervasives

Additional information

The patch is careful to only catch Env.Error exceptions, so as not to trash the backtraces of other, unplanned-for failures. After catching and reporting the exception, it terminates with "exit 2":

• keeping an uninitialized toplevel alive makes no sense
• re-raising the exception seems useless (the backtrace is trashed) and potentially confusing
• "2" was already used as an error code in topmain.ml

File attachments

• toplevel-initialization-error-reporting.patch

[vicuna]

Comment author: @johnwhitington

Excellent. I knew I must have been missing something simple, but no-one seemed to know!

http://sympa.inria.fr/sympa/arc/caml-list/2014-01/msg00017.html

[vicuna]

Comment author: @alainfrisch

I've merged the patch to trunk, also capturing Typetexp.Error. This allows to get:

$ boot/ocamlrun ./ocaml
OCaml version 4.03.0+dev11-2015-10-19

File "command line", line 1:
Error: Unbound module Pervasives