Re: [PATCH v2 1/1] quote: handle null and empty strings in sq_quote_buf_pretty()

From: Junio C Hamano <gitster@pobox.com>
Date: Aug 26, 2019, 16:20 UTC
Message-ID: <xmqq1rx7kief.fsf@gitster-ct.c.googlers.com>
In-Reply-To: <CAN+QWEZU2FqkH1jWnv==owKLsMk8XNXJh6PpF6njvB6MmKt+Dw@mail.gmail.com>

Garima Singh <garimasigit@gmail.com> writes:

Show 11 quoted lines

>> diff --git a/quote.c b/quote.c
>> index 7f2aa6faa4..6d0f8a22a9 100644
>> --- a/quote.c
>> +++ b/quote.c
>> @@ -48,6 +48,18 @@ void sq_quote_buf_pretty(struct strbuf *dst, const char *src)
>>         static const char ok_punct[] = "+,-./:=@_^";
>>         const char *p;
>>
>> +       /* In case of null tokens, warn the user of the BUG in their call. */
>> +       if (!src)
>> +               BUG("BUG can't append a NULL token to the buffer");

I thought that the BUG() macro already says "BUG" upfront, no?

Dereferencing to see if we have an empty string below will immediately give us segfault, so I would omit this check if I were writing this code, though.

>> +       /* In case of empty tokens, add a '' to ensure they
>> +        * don't get inadvertently dropped.
>> +        */

Our multi-line comments have the opening slash-asterisk and the closing asterisk-slash on their own lines.

But more importantly, "In case of empty tokens, add a ''" in this comment has zero information contents---you can read that from the code. Why we do that is what we cannot express in the code, and deserves a comment.

	/* avoid losing a zero-length string by giving nothing */

or something like that, perhaps?

Show 23 quoted lines

>> +       if (!*src) {
>> +               strbuf_addstr(dst, "''");
>> +               return;
>> +       }
>> +
>>         for (p = src; *p; p++) {
>>                 if (!isalpha(*p) && !isdigit(*p) && !strchr(ok_punct, *p)) {
>>                         sq_quote_buf(dst, src);
>> diff --git a/t/t0014-alias.sh b/t/t0014-alias.sh
>> index a070e645d7..9c176c7cbb 100755
>> --- a/t/t0014-alias.sh
>> +++ b/t/t0014-alias.sh
>> @@ -37,4 +37,12 @@ test_expect_success 'looping aliases - internal execution' '
>>  #      test_i18ngrep "^fatal: alias loop detected: expansion of" output
>>  #'
>>
>> +test_expect_success 'run-command parses empty args properly, using sq_quote_buf_pretty' '
>> +       cat >expect <<-EOF &&
>> +       fatal: cannot change to '\''alias.foo=frotz foo '\'''\'' bar'\'': No such file or directory
>> +       EOF
>> +       test_expect_code 128 git -C "alias.foo=frotz foo '\'''\'' bar" foo 2>actual &&
>> +       test_cmp expect actual
>> +'

I think it was my mistake, but we do not ahe to use "alias" for something like this, perhaps like:

    # 'git frotz' will fail with "no such command", but we are
    # not interested in its exit status.  We just want to see
    # how sq_quote_argv_pretty() shows arguments in the trace.
    GIT_TRACE=1 git frotz a "" b " " c 2>&1 |
    sed -ne "/run_command:/s/.*trace: run_command: //p" >actual &&
    echo "git-frotz a '' b ' ' c" >expect &&
    test_cmp expect actual

>> +
>>  test_done
>> --
>> gitgitgadget