Re: Runaway sed memory use in test on older sed+glibc (was "Re: [PATCH v6 1/3] test: add helper functions for git-bundle")

[Jiang Xin <worldhello.net@gmail.com>]

Ævar Arnfjörð Bjarmason <avarab@gmail.com> 于2021年5月27日周四 下午8:49写道：
>
> But no, the issue as it turns out is not Perl v.s. Sed, it's that
> there's some bug in the shellscript / tooling version (happens with both
> dash 0.5.7-4 and bash 4.3-11+deb8u2 on that box) where those expansions
> like ${A%${A#??????0?}} resolve to nothing.

That's the root cause.  It can be reproduced by running the following
test script:

```
#!/bin/sh
# test script: test.sh

test_commit_setvar () {
        var=$1 &&
        oid=1234567890123456789012345678901234567890 &&
        eval $var=$oid
}

test_commit_setvar A
echo "A: $A"
echo "Abbrev of A: ${A%${A#???????}}"
```

By running different version of dash, we can see that dash 0.5.7 fail the test:

```
$ /opt/dash/0.5.11/bin/dash test.sh
A: 1234567890123456789012345678901234567890
Abbrev of A: 1234567

$ /opt/dash/0.5.7/bin/dash test.sh
A: 1234567890123456789012345678901234567890
Abbrev of A:
```

This issue can be fixed using the following example:

```
#!/bin/sh

test_commit_setvar () {
        var=$1 &&
        oid=1234567890123456789012345678901234567890 &&
        suffix=${oid#???????} &&
        oid=${oid%$suffix} &&
        eval $var=$oid
}

test_commit_setvar A
echo "Abbrev of A: $A"
```

> Anyway, looking at this whole test file with fresh eyes this pattern
> seems very strange. You duplicated most of test_commit with this
> test_commit_setvar. It's a bit more verbosity but why not just use:
>
>     test_commit ...
>     A=$(git rev-parse HEAD)

The function "test_commit()" in "test-lib-function.sh" always creates
tags and it cannot make merge commit. So I rewrite a new function
which reuse the scaffold of "test_commit".

BTW, sorry for the late reply, will send patch later.

--
Jiang Xin