Use an (over-writable) environment variable for the gdb command

[nbigaouette]

Instead of hard-coding the command to run, using the environment
variable GDB_CMD (that defaults to gdb) allows using a different
debugger than the default gdb executable.

This gives the possibility to use cgdb as the debugger, which provides
a nicer user interface. Note that one has to use GDB_CMD="cgdb --" to
use cgdb (note the trailing --) to let cgdb pass the proper arguments
to gdb.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @alexcrichton (or someone else) soon.

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[nbigaouette-eai]

Note that the syntax ${var:-DEFAULT} should be POSIX compatible.

See http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_02

[ltratt]

This would certainly be a big help to those of us on platforms whose stock gdb doesn't work with Rust. [See https://github.com/semarie/build-rust/issues/4.]

[aidanhs]

Thanks for the PR @nbigaouette! We'll make sure @alexcrichton or another reviewer gets to your PR soon.

[alexcrichton]

Thanks @nbigaouette!

I wonder if we could perhaps call this env var RUST_GDB_CMD though? (or maybe RUST_GDB?)

Just to make it clear that it's rust-specific

[nbigaouette]

Yes, I agree the variable should be descriptive enough that it's clear what it is used for.

I like RUST_GDB. I had GDB initially but found it too generic, adding a RUST_ prefix would eliminate ambiguity.

[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit 61b7ebe has been approved by alexcrichton