END-CHOOSE directive for .nethackrc

Add an optional way to terminate the last section after a CHOOSE
directive in the run-time options file so that it's possible to
revert to common options.  If no END-CHOOSE directive is present
then the last CHOOSE section continues until the end of the file.
(All existing uses of CHOOSE already behave that way.)

Change the Guidebook to refer to OPTIONS=x, AUTOPICKUP_EXCEPTION=y,
CHOOSE=z, and so on as "directives" rather than "statements".  It
just feels like a better fit.

src/files.c

@@ -1,4 +1,4 @@
-/* NetHack 3.7	files.c	$NHDT-Date: 1595006057 2020/07/17 17:14:17 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.316 $ */
+/* NetHack 3.7	files.c	$NHDT-Date: 1596754598 2020/08/06 22:56:38 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.317 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Derek S. Ray, 2015. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -163,7 +163,8 @@ static void FDECL(adjust_prefix, (char *, int));
 static boolean FDECL(config_error_nextline, (const char *));
 static void NDECL(free_config_sections);
 static char *FDECL(choose_random_part, (char *, CHAR_P));
-static boolean FDECL(is_config_section, (const char *));
+static char *FDECL(is_config_section, (char *));
+static boolean FDECL(is_end_of_sections, (const char *));
 static boolean FDECL(handle_config_section, (char *));
 static char *FDECL(find_optparam, (const char *));
 static void FDECL(parseformat, (int *, char *));
@@ -2258,7 +2259,7 @@ int prefixid;
 
 /* Choose at random one of the sep separated parts from str. Mangles str. */
 static char *
-choose_random_part(str,sep)
+choose_random_part(str, sep)
 char *str;
 char sep;
 {
@@ -2310,29 +2311,78 @@ free_config_sections()
     }
 }
 
-static boolean
+/* check for " [ anything-except-bracket-or-empty ] # arbitrary-comment"
+   with spaces optional; returns pointer to "anything-except..." (with
+   trailing " ] #..." stripped) if ok, otherwise Null */
+static char *
 is_config_section(str)
-const char *str;
+char *str; /* trailing spaces will be stripped, ']' too iff result is good */
 {
-    const char *a = rindex(str, ']');
+    char *a, *c, *z;
 
-    return (a && *str == '[' && *(a+1) == '\0' && (int)(a - str) > 0);
+    /* remove any spaces at start and end; won't significantly interfere
+       with echoing the string in a config error message, if warranted */
+    a = trimspaces(str);
+    /* first character should be open square bracket; set pointer past it */
+    if (*a++ != '[')
+        return (char *) 0;
+    /* last character should be close bracket, ignoring any comment */
+    z = index(a, ']');
+    if (!z || z == a)
+        return (char *) 0;
+    for (c = z + 1; *c && *c != '#'; ++c)
+        continue;
+    if (*c && *c != '#')
+        return (char *) 0;
+    /* we now know that result is good; there won't be a config error
+       message so we can modify the input string */
+    *z = '\0';
+    /* 'a' points past '[' and the string ends where ']' was; remove any
+       spaces between '[' and choice-start and between choice-end and ']' */
+    return trimspaces(a);
+}
+
+static boolean
+is_end_of_sections(buf)
+const char *buf;
+{
+    /* "END-CHOOSE"; bypass match_optname()/match_varname();
+       accepts "ENDCHOOSE", "END CHOOSE", "END-CHOOSE", "END_CHOOSE" */
+    if (!strncmpi(buf, "END", 3) && buf[3]) {
+        boolean sep = index(" -_", buf[3]) != 0;
+
+        if (!strcmpi(&buf[sep ? 4 : 3], "CHOOSE")) {
+            if (!g.config_section_current)
+                config_error_add("END-CHOOSE when not in a CHOOSE section");
+            return TRUE;
+        }
+    }
+    return FALSE;
 }
 
 static boolean
 handle_config_section(buf)
 char *buf;
 {
-    if (is_config_section(buf)) {
-        char *send;
-        if (g.config_section_current) {
+    boolean was_in_section = (g.config_section_current != 0);
+    char *sect = is_config_section(buf);
+
+    if (sect) {
+        if (g.config_section_current)
             free(g.config_section_current);
+        /* is_config_section() removed brackets from 'sect' */
+        if (!g.config_section_chosen) {
+            config_error_add("Section \"[%s]\" without CHOOSE", sect);
+            return TRUE;
         }
-        g.config_section_current = dupstr(&buf[1]);
-        send = rindex(g.config_section_current, ']');
-        *send = '\0';
+        g.config_section_current = dupstr(sect);
         debugpline1("set config section: '%s'", g.config_section_current);
         return TRUE;
+    } else if (is_end_of_sections(buf)) {
+        if (was_in_section)
+            debugpline0("unset config section");
+        free_config_sections();
+        return TRUE;
     }
 
     if (g.config_section_current) {
@@ -2386,6 +2436,12 @@ char *origbuf;
        but spaces, one of them will be kept even though it leads/trails) */
     mungspaces(buf);
 
+    /* "END-CHOOSE" doesn't have a value so we need to check for it
+       before checking for that; if found here, is_end_of_sections()
+       will report a config_error */
+    if (is_end_of_sections(buf))
+        return FALSE;
+
     /* find the '=' or ':' */
     bufp = find_optparam(buf);
     if (!bufp) {
@@ -2670,8 +2726,7 @@ char *origbuf;
             retval = FALSE;
 #endif
     } else if (match_varname(buf, "WARNINGS", 5)) {
-        (void) get_uchars(bufp, translate, FALSE, WARNCOUNT,
-                          "WARNINGS");
+        (void) get_uchars(bufp, translate, FALSE, WARNCOUNT, "WARNINGS");
         assign_warnings(translate);
     } else if (match_varname(buf, "ROGUESYMBOLS", 4)) {
         if (!parsesymbols(bufp, ROGUESET)) {