allow RUST_BACKTRACE=0 to act as if unset

/# This is a combination of 16 commits.
/# The first commit's message is:
allow RUST_BACKTRACE=disabled to act as if unset

When RUST_BACKTRACE is set to "disabled" then this acts as if the env.
var is unset.

/# This is the 2nd commit message:

case insensitive "DiSaBLeD" RUST_BACKTRACE value

previously it expected a lowercase "disabled" to treat the env. var as
unset

/# This is the 3rd commit message:

RUST_BACKTRACE=0 acts as if unset

previously RUST_BACKTRACE=disabled was doing the same thing

/# This is the 4th commit message:

RUST_BACKTRACE=0|n|no|off acts as if unset

previously only RUST_BACKTRACE=0 acted as if RUST_BACKTRACE was unset
Now added more options (case-insensitive): 'n','no' and 'off'
eg. RUST_BACKTRACE=oFF

/# This is the 5th commit message:

DRY on the value of 2

DRY=don't repeat yourself
Because having to remember to keep the two places of '2' in sync is not
ideal, even though this is a simple enough case.

/# This is the 6th commit message:

Revert "DRY on the value of 2"

This reverts commit 95a0479d5cf72a2b2d9d21ec0bed2823ed213fef.

Nevermind this DRY on 2, because we already have a RY on 1,
besides the code is less readable this way...

/# This is the 7th commit message:

attempt to document unsetting RUST_BACKTRACE

/# This is the 8th commit message:

curb allocations when checking for RUST_BACKTRACE

this means we don't check for case-insensitivity anymore

/# This is the 9th commit message:

as decided, RUST_BACKTRACE=0 turns off backtrace

/# This is the 10th commit message:

RUST_TEST_NOCAPTURE=0 acts as if unset

(that is, capture is on)

Any other value acts as if nocapture is enabled (that is, capture is off)

/# This is the 11th commit message:

update other RUST_TEST_NOCAPTURE occurrences

apparently only one place needs updating

/# This is the 12th commit message:

update RUST_BACKTRACE in man page

/# This is the 13th commit message:

handle an occurrence of RUST_BACKTRACE

/# This is the 14th commit message:

ensure consistency with new rules for backtrace

/# This is the 15th commit message:

a more concise comment for RUST_TEST_NOCAPTURE

/# This is the 16th commit message:

update RUST_TEST_NOCAPTURE in man page

1 files changed, 6 insertions, 3 deletions

diff --git a/src/libtest/lib.rs b/src/libtest/lib.rs
index e4d7697a71b..e7fe128a7ae 100644
--- a/src/libtest/lib.rs
+++ b/src/libtest/lib.rs
@@ -349,8 +349,8 @@ By default, all tests are run in parallel. This can be altered with the
 RUST_TEST_THREADS environment variable when running tests (set it to 1).
 
 All tests have their standard output and standard error captured by default.
-This can be overridden with the --nocapture flag or the RUST_TEST_NOCAPTURE=1
-environment variable. Logging is not captured by default.
+This can be overridden with the --nocapture flag or setting RUST_TEST_NOCAPTURE
+environment variable to a value other than "0". Logging is not captured by default.
 
 Test Attributes:
 
@@ -399,7 +399,10 @@ pub fn parse_opts(args: &[String]) -> Option<OptRes> {
 
     let mut nocapture = matches.opt_present("nocapture");
     if !nocapture {
-        nocapture = env::var("RUST_TEST_NOCAPTURE").is_ok();
+        nocapture = match env::var("RUST_TEST_NOCAPTURE") {
+            Ok(val) => &val != "0",
+            Err(_) => false
+        };
     }
 
     let color = match matches.opt_str("color").as_ref().map(|s| &**s) {