Previously, Config was using the same method for both escaping and
parsing subsection names and config values. The goal was presumably code
savings, but unfortunately, these two pieces of the git config format
are simply different.
In git v2.15.1, Documentation/config.txt says the following about
subsection names:
"Subsection names are case sensitive and can contain any characters
except newline (doublequote `"` and backslash can be included by
escaping them as `\"` and `\\`, respectively). Section headers cannot
span multiple lines. Variables may belong directly to a section or to
a given subsection."
And, later in the same documentation section, about values:
"A line that defines a value can be continued to the next line by
ending it with a `\`; the backquote and the end-of-line are stripped.
Leading whitespaces after 'name =', the remainder of the line after
the first comment character '#' or ';', and trailing whitespaces of
the line are discarded unless they are enclosed in double quotes.
Internal whitespaces within the value are retained verbatim.
Inside double quotes, double quote `"` and backslash `\` characters
must be escaped: use `\"` for `"` and `\\` for `\`.
The following escape sequences (beside `\"` and `\\`) are recognized:
`\n` for newline character (NL), `\t` for horizontal tabulation (HT,
TAB) and `\b` for backspace (BS). Other char escape sequences
(including octal escape sequences) are invalid."
The main important differences are that subsection names have a limited
set of supported escape sequences, and do not support newlines at all,
either escaped or unescaped. Arguably, it would be easy to support
escaped newlines, but C git simply does not:
$ git config -f foo.config $'foo.bar\nbaz.quux' value
error: invalid key (newline): foo.bar
baz.quux
I468106ac was an attempt to fix one bug in escapeValue, around leading
whitespace, without having to rewrite the whole escaping/parsing code.
Unfortunately, because escapeValue was used for escaping subsection
names as well, this made it possible to write invalid config files, any
time Config#toText is called with a subsection name with trailing
whitespace, like {foo }.
Rather than pile hacks on top of hacks, fix it for real by largely
rewriting the escaping and parsing code.
In addition to fixing escape sequences, fix (and write tests for) a few
more issues in the old implementation:
* Now that we can properly parse it, always emit newlines as "\n" from
escapeValue, rather than the weird (but still supported) syntax with a
non-quoted trailing literal "\n\" before the newline. In addition to
producing more readable output and matching the behavior of C git,
this makes the escaping code much simpler.
* Disallow '\0' entirely within both subsection names and values, since
due to Unix command line argument conventions it is impossible to pass
such values to "git config".
* Properly preserve intra-value whitespace when parsing, rather than
collapsing it all to a single space.
Change-Id: I304f626b9d0ad1592c4e4e449a11b136c0f8b3e3
31a2d09c9c