chainlint: recognize multi-line quoted strings more robustly

chainlint.sed recognizes multi-line quoted strings within subshells:

    echo "abc
        def" >out &&

so it can avoid incorrectly classifying lines internal to the string as
breaking the &&-chain. To identify the first line of a multi-line
string, it checks if the line contains a single quote. However, this is
fragile and can be easily fooled by a line containing multiple strings:

    echo "xyz" "abc
        def" >out &&

Make detection more robust by checking for an odd number of quotes
rather than only a single one.

(Escaped quotes are not handled, but support may be added later.)

The original multi-line string recognizer rather cavalierly threw away
all but the final quote, whereas the new one is careful to retain all
quotes, so the "expected" output of a couple existing chainlint tests is
updated to account for this new behavior.

Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/chainlint.sed

@@ -151,10 +151,10 @@ s/.*\n//
 :slurp
 # incomplete line "...\"
 /\\$/bincomplete
-# multi-line quoted string "...\n..."
+# multi-line quoted string "...\n..."?
-/^[^"]*"[^"]*$/bdqstring
+/"/bdqstring
-# multi-line quoted string '...\n...' (but not contraction in string "it's so")
+# multi-line quoted string '...\n...'? (but not contraction in string "it's")
-/^[^']*'[^']*$/{
+/'/{
 	/"[^'"]*'[^'"]*"/!bsqstring
 }
 :folded
@@ -250,20 +250,32 @@ N
 s/\\\n//
 bslurp
 
-# found multi-line double-quoted string "...\n..." -- slurp until end of string
+# check for multi-line double-quoted string "...\n..." -- fold to one line
 :dqstring
-s/"//g
+# remove all quote pairs
+s/"\([^"]*\)"/@!\1@!/g
+# done if no dangling quote
+/"/!bdqdone
+# otherwise, slurp next line and try again
 N
 s/\n//
-/"/!bdqstring
+bdqstring
+:dqdone
+s/@!/"/g
 bfolded
 
-# found multi-line single-quoted string '...\n...' -- slurp until end of string
+# check for multi-line single-quoted string '...\n...' -- fold to one line
 :sqstring
-s/'//g
+# remove all quote pairs
+s/'\([^']*\)'/@!\1@!/g
+# done if no dangling quote
+/'/!bsqdone
+# otherwise, slurp next line and try again
 N
 s/\n//
-/'/!bsqstring
+bsqstring
+:sqdone
+s/@!/'/g
 bfolded
 
 # found here-doc -- swallow it to avoid false hits within its body (but keep

t/chainlint/here-doc-multi-line-string.expect

@@ -1,4 +1,4 @@
 (
-?!AMP?!	cat && echo multi-line	string"
+?!AMP?!	cat && echo "multi-line	string"
 	bap
 >)

t/chainlint/multi-line-string.expect

@@ -1,9 +1,15 @@
 (
-	x=line 1		line 2		line 3" &&
+	x="line 1		line 2		line 3" &&
-?!AMP?!	y=line 1		line2'
+?!AMP?!	y='line 1		line2'
 	foobar
 >) &&
 (
 	echo "there's nothing to see here" &&
 	exit
+>) &&
+(
+	echo "xyz" "abc		def		ghi" &&
+	echo 'xyz' 'abc		def		ghi' &&
+	echo 'xyz' "abc		def		ghi" &&
+	barfoo
 >)

t/chainlint/multi-line-string.test

@@ -12,4 +12,16 @@
 # LINT: starting multi-line single-quoted string
 	echo "there's nothing to see here" &&
 	exit
+) &&
+(
+	echo "xyz" "abc
+		def
+		ghi" &&
+	echo 'xyz' 'abc
+		def
+		ghi' &&
+	echo 'xyz' "abc
+		def
+		ghi" &&
+	barfoo
 )