nsc: Rename nstr_exec_val() to nstr_eval() and tighten contract

nstr_exec_val() can produce three different error values: NSC_NOTYPE
on invalid category, invalid type with zero val_as.lng on invalid type
(this is a bug), and the wanted type with zero val_s when it can't
coerce.  None of these should ever happen.

Fix it to always produce an NSC_NOTYPE error value.  Fix up callers to
check for it.

Specify the result's type is promoted on success.  Ensure it is even
when the argument is NSC_VAL with an unpromoted type, which is
invalid.

Signed-off-by: Markus Armbruster <armbru@pond.sub.org>

include/nsc.h

@@ -286,8 +286,8 @@ extern struct symbol sector_navigation[];
 
 /* src/lib/common/nstreval.c */
 extern struct valstr *nstr_mksymval(struct valstr *, struct castr *, int);
-extern struct valstr *nstr_exec_val(struct valstr *, natid, void *,
+extern struct valstr *nstr_eval(struct valstr *, natid, void *,
-				    enum nsc_type);
+				enum nsc_type);
 extern int nstr_promote(int);
 extern char *symbol_by_value(int, struct symbol *);
 /* src/lib/global/nsc.c */

src/lib/commands/surv.c

@@ -28,6 +28,7 @@
  *
  *  Known contributors to this file:
  *     Dave Pare, 1986
+ *     Markus Armbruster, 2004-2014
  */
 
 #include <config.h>
@@ -135,7 +136,9 @@ code_char(struct valstr val, struct sctstr *sp)
     int n;
     int large = val.val_type != NSC_CHAR && val.val_type != NSC_UCHAR;
 
-    nstr_exec_val(&val, player->cnum, sp, NSC_LONG);
+    nstr_eval(&val, player->cnum, sp, NSC_LONG);
+    if (CANT_HAPPEN(val.val_type != NSC_LONG))
+	return ' ';
     amt = val.val_as.lng;
     if (amt <= 0)
 	return ' ';

src/lib/common/ef_verify.c

@@ -169,7 +169,7 @@ verify_row(int type, int row)
 	    if (ca[i].ca_table == EF_BAD)
 		continue;
 	    nstr_mksymval(&val, &ca[i], j);
-	    nstr_exec_val(&val, 0, row_ref, NSC_NOTYPE);
+	    nstr_eval(&val, 0, row_ref, NSC_NOTYPE);
 	    if (CANT_HAPPEN(val.val_type != NSC_LONG)) {
 		ret_val = -1;
 		continue;

src/lib/common/nstreval.c

@@ -29,7 +29,7 @@
  *  Known contributors to this file:
  *     Dave Pare, 1989
  *     Steve McClure, 1997
- *     Markus Armbruster, 2004-2008
+ *     Markus Armbruster, 2004-2014
  */
 
 #include <config.h>
@@ -59,16 +59,19 @@ nstr_mksymval(struct valstr *val, struct castr *ca, int idx)
 
 /*
  * Evaluate VAL.
- * If VAL is symbolic, evaluate it into a promoted value type.
+ * If VAL has category NSC_OFF, read the value from the context object
- * Translate it for country CNUM (coordinate system and contact
+ * PTR, and translate it for country CNUM (coordinate system and
- * status), except when CNUM is NATID_BAD.
+ * contact status).  No translation when CNUM is NATID_BAD.
  * PTR points to a context object of the type that was used to compile
  * the value.
  * Unless WANT is NSC_NOTYPE, coerce the value to promoted value type
  * WANT.  VAL must be coercible.
+ * The result's type is promoted on success, NSC_NOTYPE on error.
+ * In either case, the category is NSC_VAL.
+ * Return VAL.
  */
 struct valstr *
-nstr_exec_val(struct valstr *val, natid cnum, void *ptr, enum nsc_type want)
+nstr_eval(struct valstr *val, natid cnum, void *ptr, enum nsc_type want)
 {
     char *memb_ptr;
     enum nsc_type valtype;
@@ -82,6 +85,8 @@ nstr_exec_val(struct valstr *val, natid cnum, void *ptr, enum nsc_type want)
     switch (val->val_cat) {
     case NSC_VAL:
 	valtype = val->val_type;
+	if (CANT_HAPPEN(!NSC_IS_PROMOTED(valtype)))
+	    valtype = nstr_promote(valtype);
 	break;
     case NSC_OFF:
 	if (val->val_as.sym.get) {
@@ -168,6 +173,7 @@ nstr_exec_val(struct valstr *val, natid cnum, void *ptr, enum nsc_type want)
 	case NSC_STRING:
 	    val->val_as.str.base = ((char **)memb_ptr)[idx];
 	    val->val_as.str.maxsz = INT_MAX;
+				/* really SIZE_MAX, but that's C99 */
 	    valtype = NSC_STRING;
 	    break;
 	case NSC_TIME:
@@ -175,7 +181,7 @@ nstr_exec_val(struct valstr *val, natid cnum, void *ptr, enum nsc_type want)
 	    break;
 	default:
 	    CANT_REACH();
-	    val->val_as.lng = 0;
+	    valtype = NSC_NOTYPE;
 	}
 	val->val_cat = NSC_VAL;
 	break;
@@ -194,11 +200,8 @@ nstr_exec_val(struct valstr *val, natid cnum, void *ptr, enum nsc_type want)
 	}
     }
 
-    if (CANT_HAPPEN(valtype != want && want != NSC_NOTYPE)) {
+    if (CANT_HAPPEN(valtype != want && want != NSC_NOTYPE))
-	/* make up an error value */
+	valtype = NSC_NOTYPE;
-	valtype = want;
-	memset(&val->val_as, 0, sizeof(val->val_as));
-    }
 
     val->val_type = valtype;
     return val;

src/lib/common/xdump.c

@@ -112,7 +112,7 @@ xdeval(struct valstr *val, struct xdstr *xd,
        struct castr *ca, void *ptr, int idx)
 {
     nstr_mksymval(val, ca, idx);
-    return nstr_exec_val(val, xd->cnum, ptr, NSC_NOTYPE);
+    return nstr_eval(val, xd->cnum, ptr, NSC_NOTYPE);
 }
 
 /*

src/lib/subs/nstr.c

@@ -29,7 +29,7 @@
  *  Known contributors to this file:
  *     Dave Pare, 1989
  *     Steve McClure, 1997
- *     Markus Armbruster, 2004-2013
+ *     Markus Armbruster, 2004-2014
  */
 
 #include <config.h>
@@ -231,7 +231,8 @@ strnncmp(char *s1, size_t sz1, char *s2, size_t sz2)
 int
 nstr_exec(struct nscstr *np, int ncond, void *ptr)
 {
-    int i, op, optype, cmp;
+    int i, op, cmp;
+    enum nsc_type optype;
     struct valstr lft, rgt;
 
     for (i = 0; i < ncond; ++i) {
@@ -240,9 +241,11 @@ nstr_exec(struct nscstr *np, int ncond, void *ptr)
 	if (np[i].lft.val_cat == NSC_NOCAT || np[i].rgt.val_cat == NSC_NOCAT)
 	    return 0;
 	lft = np[i].lft;
-	nstr_exec_val(&lft, player->cnum, ptr, optype);
+	nstr_eval(&lft, player->cnum, ptr, optype);
 	rgt = np[i].rgt;
-	nstr_exec_val(&rgt, player->cnum, ptr, optype);
+	nstr_eval(&rgt, player->cnum, ptr, optype);
+	if (CANT_HAPPEN(lft.val_type != optype || rgt.val_type != optype))
+	    return 0;
 	switch (optype) {
 	case NSC_LONG:
 	    if (!EVAL(op, lft.val_as.lng, rgt.val_as.lng))