[PATCH 6/7] completion: fix expansion issue in __gitcomp()

["SZEDER Gábor" <szeder@ira.uka.de>]

The compgen Bash-builtin performs expansion on all words in the
wordlist given to its -W option, breaking Git's completion script when
words passed to __gitcomp() contain expandable substrings.

In __gitcomp() we only use a small subset ot compgen's functionality,
namely the filtering of matching possible completion words and adding
a prefix to each of those words; suffix is added by the __gitcomp_1()
helper function instead.  Now, since we already have to iterate over
all words in the wordlist to append a trailing space if necessary, we
can check in the same loop whether a word matches the word to be
completed and store matching words with possible prefix and/or suffix
in the COMPREPLY array.  This way we achieve the same functionality
without the compgen builtin and, more importantly, without it's
problematic expansions.

An additional benefit, especially for Windows/MSysGit users, is the
loss of two subshells, one to run __gitcomp_1() and the other to run
the compgen builtin.

Note, that like the previous patch for __gitcomp_nl(), this patch
doesn't quote expandable words either, but that could be implemented
later on top by unquoting $cur and then quoting what get stored in
COMPREPLY.

Also update the function's description a bit.

Signed-off-by: SZEDER Gábor <szeder@ira.uka.de>
---
 contrib/completion/git-completion.bash | 27 ++++++++++++++++++++-------
 t/t9902-completion.sh                  |  2 +-
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/contrib/completion/git-completion.bash b/contrib/completion/git-completion.bash
index 65196ddd..283ef99b 100644
--- a/contrib/completion/git-completion.bash
+++ b/contrib/completion/git-completion.bash
@@ -225,12 +225,13 @@ _get_comp_words_by_ref ()
 fi
 fi
 
-# Generates completion reply with compgen, appending a space to possible
-# completion words, if necessary.
+# Generates completion reply for the word in $cur, appending a space to
+# possible completion words, if necessary.
 # It accepts 1 to 4 arguments:
 # 1: List of possible completion words.
 # 2: A prefix to be added to each possible completion word (optional).
-# 3: Generate possible completion matches for this word (optional).
+# 3: Generate possible completion matches for this word instead of $cur
+#    (optional).
 # 4: A suffix to be appended to each possible completion word (optional).
 __gitcomp ()
 {
@@ -241,10 +242,22 @@ __gitcomp ()
 		COMPREPLY=()
 		;;
 	*)
-		local IFS=$'\n'
-		COMPREPLY=($(compgen -P "${2-}" \
-			-W "$(__gitcomp_1 "${1-}" "${4-}")" \
-			-- "$cur_"))
+		local i=0 c IFS=$' \t\n'
+		for c in $1; do
+			case $c in
+			"$cur_"*)
+				c="$c${4-}"
+				case $c in
+				--*=*|*.) ;;
+				*) c="$c " ;;
+				esac
+				COMPREPLY[$i]="${2-}$c"
+				i=$((++i))
+				;;
+			*)
+				;;
+			esac
+		done
 		;;
 	esac
 }
diff --git a/t/t9902-completion.sh b/t/t9902-completion.sh
index fa289324..d08f4259 100755
--- a/t/t9902-completion.sh
+++ b/t/t9902-completion.sh
@@ -156,7 +156,7 @@ test_expect_success '__gitcomp - suffix' '
 	test_cmp expected out
 '
 
-test_expect_failure '__gitcomp - doesnt fail because of invalid variable name' '
+test_expect_success '__gitcomp - doesnt fail because of invalid variable name' '
 	(
 		__gitcomp "$invalid_variable_name"
 	)
-- 
1.8.0.220.g4d14ece