extensions: show traceback on load failure if --traceback flag is set
Before this patch, there was no handy way to investigate the reason why
extension couldn't be loaded.
If ui.debug is set, tracebacks of both "hgext.foo" and "foo" are displayed
because the first ImportError could occur at very deep dependency module.
$ cat <<EOF > merge
> import sys, os
> print "merging for", os.path.basename(sys.argv[1])
> EOF
$ HGMERGE="python ../merge"; export HGMERGE
$ hg init A1
$ cd A1
$ echo This is file foo1 > foo
$ echo This is file bar1 > bar
$ hg add foo bar
$ hg commit -m "commit text"
$ cd ..
$ hg clone A1 B1
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd A1
$ rm bar
$ hg remove bar
$ hg commit -m "commit test"
$ cd ../B1
$ echo This is file foo22 > foo
$ hg commit -m "commit test"
$ cd ..
$ hg clone A1 A2
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg clone B1 B2
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd A1
$ hg pull ../B1
pulling from ../B1
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg merge
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg commit -m "commit test"
bar should remain deleted.
$ hg manifest --debug
f9b0e817f6a48de3564c6b2957687c5e7297c5a0 644 foo
$ cd ../B2
$ hg pull ../A2
pulling from ../A2
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg merge
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg commit -m "commit test"
bar should remain deleted.
$ hg manifest --debug
f9b0e817f6a48de3564c6b2957687c5e7297c5a0 644 foo
$ cd ..