hush: rework input char buffering to allow more than one-deep peek

This fixes backslash+newline continuation in
	$VAR\
	NAME
construct. (ash has a bug there as well).

function                                             old     new   delta
file_peek2                                             -      74     +74
parse_dollar                                         746     773     +27
expand_vars_to_list                                 1143    1167     +24
setup_string_in_str                                   32      46     +14
setup_file_in_str                                     33      47     +14
file_get                                             264     278     +14
static_peek2                                           -       7      +7
file_peek                                             91      72     -19
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 5/1 up/down: 174/-19)           Total: 155 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/ash_test/ash-vars/var_serial.right

@@ -0,0 +1,5 @@
+Assignments only: c=a
+Assignments and a command: c=a
+Assignments and a builtin: c=a
+Assignments and a function: c=a
+Done

shell/ash_test/ash-vars/var_serial.tests

@@ -0,0 +1,22 @@
+a=a
+
+b=b
+c=c
+# Second assignment depends on the first:
+b=$a c=$b
+echo Assignments only: c=$c
+
+b=b
+c=c
+b=$a c=$b "$THIS_SH" -c 'echo Assignments and a command: c=$c'
+
+b=b
+c=c
+b=$a c=$b eval 'echo Assignments and a builtin: c=$c'
+
+b=b
+c=c
+f() { echo Assignments and a function: c=$c; }
+b=$a c=$b f
+
+echo Done

shell/ash_test/ash-vars/var_subst_in_for.right

@@ -0,0 +1,40 @@
+Testing: in x y z
+.x.
+.y.
+.z.
+Testing: in u $empty v
+.u.
+.v.
+Testing: in u " $empty" v
+.u.
+. .
+.v.
+Testing: in u $empty $empty$a v
+.u.
+.a.
+.v.
+Testing: in $a_b
+.a.
+.b.
+Testing: in $*
+.abc.
+.d.
+.e.
+Testing: in $@
+.abc.
+.d.
+.e.
+Testing: in -$*-
+.-abc.
+.d.
+.e-.
+Testing: in -$@-
+.-abc.
+.d.
+.e-.
+Testing: in $a_b -$a_b-
+.a.
+.b.
+.-a.
+.b-.
+Finished

shell/ash_test/ash-vars/var_subst_in_for.tests

@@ -0,0 +1,40 @@
+if test $# = 0; then
+    exec "$THIS_SH" "$0" abc "d e"
+fi
+
+echo 'Testing: in x y z'
+for a in x y z; do echo ".$a."; done
+
+echo 'Testing: in u $empty v'
+empty=''
+for a in u $empty v; do echo ".$a."; done
+
+echo 'Testing: in u " $empty" v'
+empty=''
+for a in u " $empty" v; do echo ".$a."; done
+
+echo 'Testing: in u $empty $empty$a v'
+a='a'
+for a in u $empty $empty$a v; do echo ".$a."; done
+
+echo 'Testing: in $a_b'
+a_b='a b'
+for a in $a_b; do echo ".$a."; done
+
+echo 'Testing: in $*'
+for a in $*; do echo ".$a."; done
+
+echo 'Testing: in $@'
+for a in $@; do echo ".$a."; done
+
+echo 'Testing: in -$*-'
+for a in -$*-; do echo ".$a."; done
+
+echo 'Testing: in -$@-'
+for a in -$@-; do echo ".$a."; done
+
+echo 'Testing: in $a_b -$a_b-'
+a_b='a b'
+for a in $a_b -$a_b-; do echo ".$a."; done
+
+echo Finished

shell/ash_test/ash-vars/var_unbackslash.right

@@ -0,0 +1,11 @@
+b1=-qwerty-t-\-"-`---z-*-?-
+b1=-qwerty-t-\-"-`---z-*-?-
+b2=-qwerty-\t-\-"-`-\--\z-\*-\?-
+b2=-qwerty-\t-\-"-`-\--\z-\*-\?-
+b3=-$a-\t-\\-\"-\`-\--\z-\*-\?-
+b3=-$a-\t-\\-\"-\`-\--\z-\*-\?-
+c=-$a-\t-\\-\"-\`-\--\z-\*-\?-
+c=-$a-\t-\\-\"-\`-\--\z-\*-\?-
+c=-$a-\t-\\-\"-\`-\--\z-\*-\?-
+c=-$a-\t-\\-\"-\`-\--\z-\*-\?-
+Done: 0

shell/ash_test/ash-vars/var_unbackslash.tests

@@ -0,0 +1,23 @@
+# Test for correct handling of backslashes
+a=qwerty
+
+b=-$a-\t-\\-\"-\`-\--\z-\*-\?-
+echo b1=$b
+echo "b1=$b"
+b="-$a-\t-\\-\"-\`-\--\z-\*-\?-"
+echo b2=$b
+echo "b2=$b"
+b='-$a-\t-\\-\"-\`-\--\z-\*-\?-'
+echo b3=$b
+echo "b3=$b"
+
+c=$b
+echo "c=$c"
+c=${b}
+echo "c=$c"
+c="$b"
+echo "c=$c"
+c="${b}"
+echo "c=$c"
+
+echo "Done: $?"

shell/ash_test/ash-vars/var_unbackslash1.right

@@ -0,0 +1,3 @@
+Ok
+Ba d
+Ok

shell/ash_test/ash-vars/var_unbackslash1.tests

@@ -0,0 +1,15 @@
+ad="Ok"
+a="Ba"
+
+# "Ok"
+echo $a\
+d
+
+# This variable contains backslash+newline!
+e='echo $a\
+d'
+
+# "Ba d"
+eval $e
+# "Ok"
+eval "$e"

shell/hush_test/hush-vars/var_unbackslash1.right

@@ -0,0 +1,3 @@
+Ok
+Ba d
+Ok

shell/hush_test/hush-vars/var_unbackslash1.tests

@@ -0,0 +1,15 @@
+ad="Ok"
+a="Ba"
+
+# "Ok"
+echo $a\
+d
+
+# This variable contains backslash+newline!
+e='echo $a\
+d'
+
+# "Ba d"
+eval $e
+# "Ok"
+eval "$e"