Fix nested commands in interactive mode triggering prompt2 (issue #19)

Save and restore cmd_mode across interpolation parsing so that
luaX_readcommandcont resumes in the correct mode after a nested
backtick command inside ${...}.

issues/19-nested-commands-prompt2.md

@@ -1,6 +1,6 @@
 # 19 — Nested commands in interactive mode trigger prompt2
 
-**Status:** open
+**Status:** done
 
 Running nested commands in an interactive command drops into prompt2 when it shouldn't:
 

llex.c

@@ -512,6 +512,7 @@ static int read_command_body (LexState *ls, SemInfo *seminfo) {
           /* store fragment so far */
           seminfo->ts = luaX_newstring(ls, luaZ_buffer(ls->buff),
                                            luaZ_bufflen(ls->buff));
+          ls->saved_cmd_mode = ls->cmd_mode;  /* save for readcommandcont */
           return interactive ? TK_INTERACTIVE_INTERP : TK_COMMAND_INTERP;
         }
         else {
@@ -571,6 +572,7 @@ static int read_command (LexState *ls, SemInfo *seminfo) {
 ** consumed the '}' that closes an interpolated ${expr}.
 */
 int luaX_readcommandcont (LexState *ls) {
+  ls->cmd_mode = ls->saved_cmd_mode;  /* restore mode from before interpolation */
   int tk = read_command_body(ls, &ls->t.seminfo);
   ls->t.token = tk;
   return tk;

llex.h

@@ -83,6 +83,7 @@ typedef struct LexState {
   TString *brkn;  /* "break" name (used as a label) */
   TString *glbn;  /* "global" name (when not a reserved word) */
   lu_byte cmd_mode;  /* 0=normal, 1=backtick command, 2=interactive command */
+  lu_byte saved_cmd_mode;  /* cmd_mode to restore after interpolation */
 } LexState;
 
 

testes/lush/interactive.lua

@@ -86,6 +86,14 @@ do
   assert(run_cmd() == 0)
 end
 
+-- ===== NESTED BACKTICK IN INTERPOLATION (issue #19) =====
+
+do
+  local result = `echo hello`
+!echo ${result.stdout}
+  assert(_.code == 0)
+end
+
 -- ===== EMPTY COMMAND (just whitespace after !) =====
 
 do