Re: [PATCH v3 1/1] contrib: add coverage-diff script

"Derrick Stolee via GitGitGadget" [off-list ref] writes:

+files=$(git diff --name-only $V1 $V2 -- *.c)

You'd want to quote that *.c from the shell, i.e. either one of
these

	files=$(git diff --name-only $V1 $V2 -- \*.c)
	files=$(git diff --name-only $V1 $V2 -- '*.c')

otherwise you'd lose things like "builtin/am.c", I'd think.

+
+for file in $files
+do

I know this is only for running in _our_ source tree, and we do not
have a source with $IFS in it, so I'd declare that this is OK.  It
would be good to document that assumption in red capital letters at
the beginning of this loop, though ;-)

	# Note: this script is only for our codebase and we rely on
	# the fact that the pathnames of our source files do not
	# have any funny characters---letting the shell split $files
	# list at $IFS boundary is very much intentional, and not
	# quoting "$file" in the code below also is.  Don't imitate
	# this in scripts that are meant to handle random end-user
	# repositories!
	for file in $files
	do
		...

+	git diff $V1 $V2 -- $file \
+		| diff_lines \
+		| sort >new_lines.txt

I do not see a strong reason why we would want to limit $V1 and $V2
to branch names and raw commit object names, and quoting them in dq
pair is a cheap fix to allow things like

	$ contrib/coverage-diff.sh master 'pu^{/^### match next}'

so let's do so.

Could you cut lines _after_ typing a pipe and omit backslashes, i.e.

	git diff "$V1" "$V2" -- $file |
	diff_lines |
	sort >new_lines.txt

It seems to be personal taste whether to indent the second and
subsequent lines; I do not care if you indent or if you align too
much either way (but I have moderate perference to align).  

But I do not want to see people type unnecessary backslashes.  This
is not limited to just this pipeline but elsewhere in the script.

+	if ! test -s new_lines.txt
+	then
+		continue
+	fi
+
+	hash_file=$(echo $file | sed "s/\//\#/")
+	sed -ne '/#####:/{
+			s/    #####://
+			s/:.*//
+			s/ //g
+			p
+		}' "$hash_file.gcov" \
+		| sort >uncovered_lines.txt
+
+	comm -12 uncovered_lines.txt new_lines.txt \
+		| sed -e 's/$/\)/' \
+		| sed -e 's/^/\t/' \

Do you need two sed invocations for this, or would

	sed -e 's/$/\)/' -e '/^/	/'

work as well?  By the way """The meaning of an unescaped <backslash>
immediately followed by any character other than '&', <backslash>, a
digit, <newline>, or the delimiter character used for this command,
is unspecified."""[*1*] so '\t' on the replacement side is a no-no
in the portability department.

	Reference. *1*
	http://pubs.opengroup.org/onlinepubs/9699919799/utilities/sed.html

+		>uncovered_new_lines.txt
+
+	grep -q '[^[:space:]]' < uncovered_new_lines.txt && \

Lose the backslash at the end.  The shell knows that you haven't
finished your sentence when it sees a line that ends with &&, || or
a pipe |, so there is no need to tell it redundantly that you have
more things to say with the backslash.

+		echo $file && \
+		git blame -c $file \
+			| grep -f uncovered_new_lines.txt
+
+	rm -f new_lines.txt uncovered_lines.txt uncovered_new_lines.txt
+done

Near the begininng (like just before the "for file in $files" loop),
you can probably have a trap to make sure these are removed upon
exit, e.g.

    trap 'rm -f new_lines.txt uncovered_lines.txt uncovered_new_lines.txt' 0