From 947a372f5860a76fcafb4a2845abc322e440d6fc Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Wed, 31 Oct 2018 14:54:45 -0300
Subject: State in generic 'for' acts as a to-be-closed variable

The implicit variable 'state' in a generic 'for' is marked as a
to-be-closed variable, so that the state will be closed as soon
as the loop ends, no matter how.

Taking advantage of this new facility, the call 'io.lines(filename)'
now returns the open file as a second result. Therefore,
an iteraction like 'for l in io.lines(name)...' will close the
file even when the loop ends with a break or an error.
---
 liolib.c | 35 +++++++++++++++++++++++++++++------
 1 file changed, 29 insertions(+), 6 deletions(-)

(limited to 'liolib.c')

diff --git a/liolib.c b/liolib.c
index 3dc509bd..5881b029 100644
--- a/liolib.c
+++ b/liolib.c
@@ -354,12 +354,22 @@ static int io_readline (lua_State *L);
 */
 #define MAXARGLINE	250
 
+/*
+** Auxiliar function to create the iteration function for 'lines'.
+** The iteration function is a closure over 'io_readline', with
+** the following upvalues:
+** 1) The file being read (first value in the stack)
+** 2) the number of arguments to read
+** 3) a boolean, true iff file has to be closed when finished ('toclose')
+** *) a variable number of format arguments (rest of the stack)
+*/
 static void aux_lines (lua_State *L, int toclose) {
   int n = lua_gettop(L) - 1;  /* number of arguments to read */
   luaL_argcheck(L, n <= MAXARGLINE, MAXARGLINE + 2, "too many arguments");
+  lua_pushvalue(L, 1);  /* file */
   lua_pushinteger(L, n);  /* number of arguments to read */
   lua_pushboolean(L, toclose);  /* close/not close file when finished */
-  lua_rotate(L, 2, 2);  /* move 'n' and 'toclose' to their positions */
+  lua_rotate(L, 2, 3);  /* move the three values to their positions */
   lua_pushcclosure(L, io_readline, 3 + n);
 }
 
@@ -371,6 +381,11 @@ static int f_lines (lua_State *L) {
 }
 
 
+/*
+** Return an iteration function for 'io.lines'. If file has to be
+** closed, also returns the file itself as a second result (to be
+** closed as the state at the exit of a generic for).
+*/
 static int io_lines (lua_State *L) {
   int toclose;
   if (lua_isnone(L, 1)) lua_pushnil(L);  /* at least one argument */
@@ -386,8 +401,13 @@ static int io_lines (lua_State *L) {
     lua_replace(L, 1);  /* put file at index 1 */
     toclose = 1;  /* close it after iteration */
   }
-  aux_lines(L, toclose);
-  return 1;
+  aux_lines(L, toclose);  /* push iteration function */
+  if (toclose) {
+    lua_pushvalue(L, 1);  /* file will be second result */
+    return 2;
+  }
+  else
+    return 1;
 }
 
 
@@ -453,7 +473,7 @@ static int readdigits (RN *rn, int hex) {
 /*
 ** Read a number: first reads a valid prefix of a numeral into a buffer.
 ** Then it calls 'lua_stringtonumber' to check whether the format is
-** correct and to convert it to a Lua number
+** correct and to convert it to a Lua number.
 */
 static int read_number (lua_State *L, FILE *f) {
   RN rn;
@@ -604,6 +624,9 @@ static int f_read (lua_State *L) {
 }
 
 
+/*
+** Iteration function for 'lines'.
+*/
 static int io_readline (lua_State *L) {
   LStream *p = (LStream *)lua_touserdata(L, lua_upvalueindex(1));
   int i;
@@ -624,8 +647,8 @@ static int io_readline (lua_State *L) {
       return luaL_error(L, "%s", lua_tostring(L, -n + 1));
     }
     if (lua_toboolean(L, lua_upvalueindex(3))) {  /* generator created file? */
-      lua_settop(L, 0);
-      lua_pushvalue(L, lua_upvalueindex(1));
+      lua_settop(L, 0);  /* clear stack */
+      lua_pushvalue(L, lua_upvalueindex(1));  /* push file at index 1 */
       aux_close(L);  /* close it */
     }
     return 0;
-- 
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