Document fork, exec, wait and redirect2null Lua functions as deprecated

Rpm scriptlets should have no business dealing with this level of
detail in process control, rpm.execut() is much saner and safer
for scriptlet needs. We can't just remove because this is a public
API with known users (eg glibc in Fedora), but we can at least document
these as deprecated with noisy warnings.

fork() and exec() are the main "problems" here, but wait() and
redirect2null() become meaningless once you take the first two away.

Fixes: #2420

docs/manual/lua.md

@@ -292,7 +292,7 @@ f = f:reopen('r.gzdio')
 print(f:read())}
 ```
 
-#### redirect2null(fdno)
+#### redirect2null(fdno) (DEPRECATED)
 
 Redirect file descriptor fdno to /dev/null (rpm >= 4.16, in rpm 4.13-4.15
 this was known as posix.redirect2null())
@@ -307,6 +307,9 @@ elseif pid > 0 then
 end
 ```
 
+This function is deprecated and scheduled for removal in 6.0,
+use `rpm.execute()` instead.
+
 #### undefine(name)
 
 Undefine a macro (rpm >= 4.14.0)
@@ -440,10 +443,12 @@ if not posix.chmod(f, 100) then
 end
 ```
 
-#### exec(path [, args...])
+#### exec(path [, args...]) (DEPRECATED)
 
 Execute a program. This may only be performed after posix.fork().
-For executing external commands it's recommended to use `rpm.execute()` instead.
+
+This function is deprecated and scheduled for removal in 6.0,
+use `rpm.execute()` instead.
 
 #### files([path])
 
@@ -456,10 +461,12 @@ for f in posix.files('/') do
 end
 ```
 
-#### fork()
+#### fork() (DEPRECATED)
 
 Fork a new process. 
-For executing external commands it's recommended to use `rpm.execute()` instead.
+
+This function is deprecated and scheduled for removal in 6.0,
+use `rpm.execute()` instead.
 
 ```
 pid = posix.fork()
@@ -724,7 +731,7 @@ posix.mkdir('aaa')
 posix.utime('aaa', 0, 0)
 ```
 
-#### wait([pid])
+#### wait([pid]) (DEPRECATED)
 
 Wait for a child process. If pid is specified wait for that particular child.
 
@@ -737,6 +744,9 @@ elseif pid > 0 then
 end
 ```
 
+This function is deprecated and scheduled for removal in 6.0,
+use `rpm.execute()` instead.
+
 #### setenv(name, value [, overwrite])
 
 Change or add an environment variable. The optional overwrite is a boolean

rpmio/lposix.c

@@ -45,6 +45,10 @@
 
 extern int _rpmlua_have_forked;
 
+#define check_deprecated() \
+    fprintf(stderr, \
+	"warning: posix.%s(): .fork(), .exec(), .wait() and .redirect2null() are deprecated, use rpm.execute() instead\n", __func__+1)
+
 static const char *filetype(mode_t m)
 {
 	if (S_ISREG(m))		return "regular";
@@ -333,6 +337,8 @@ static int Pmkfifo(lua_State *L)		/** mkfifo(path) */
 
 static int Pexec(lua_State *L)			/** exec(path,[args]) */
 {
+	check_deprecated();
+
 	const char *path = luaL_checkstring(L, 1);
 	int i,n=lua_gettop(L);
 	char **argv;
@@ -355,6 +361,8 @@ static int Pexec(lua_State *L)			/** exec(path,[args]) */
 
 static int Pfork(lua_State *L)			/** fork() */
 {
+	check_deprecated();
+
 	pid_t pid = fork();
 	if (pid == 0) {
 	    _rpmlua_have_forked = 1;
@@ -365,6 +373,8 @@ static int Pfork(lua_State *L)			/** fork() */
 
 static int Pwait(lua_State *L)			/** wait([pid]) */
 {
+	check_deprecated();
+
 	pid_t pid = luaL_optinteger(L, 1, -1);
 	return pushresult(L, waitpid(pid, NULL, 0), NULL);
 }

tests/rpmmacro.at

@@ -1377,6 +1377,8 @@ runroot_other rpmlua -e 'pid = posix.fork(); if pid == 0 then a,b,c=rpm.redirect
 [0],
 [nil	Bad file descriptor	9.0
 ],
-[warning: runaway fork() in Lua script]
+[warning: posix.fork(): .fork(), .exec(), .wait() and .redirect2null() are deprecated, use rpm.execute() instead
+warning: posix.wait(): .fork(), .exec(), .wait() and .redirect2null() are deprecated, use rpm.execute() instead
+warning: runaway fork() in Lua script]
 )
 RPMTEST_CLEANUP