Wizards learn about spellbooks as they enhance their spell skills

Previously, Wizards got a boost to the chance of writing unknown
spellbooks based purely on being a Wizard (with the chance still
luck-based), leading to a very large power spike when the Wizard
gained access to a luckstone and the ability to max out luck.
This had two main issues: this power spike came *after* the major
early-game difficulty spike, often leaving Wizards forced to deal
with it without having appropriate spells; and it promotes
grinding (for Luck and for Magicbane) at an early point in the
game, meaning that the Wizard early game effectively followed a
sequence of extreme difficulty -> grinding -> minimal difficulty,
which isn't very good balance-wise.

With this commit, Wizards lose their advantage to writing unknown
spellbooks by guessing, and instead learn spellbook IDs based on
their spell skills (advancing a skill gives knowledge of higher-
level spellbooks). This means that writing unknown spellbooks
becomes guaranteed with sufficient skill, but has no advantage
over non-Wizards in schools where the Wixard does not have
sufficient skill.

Due to Wizards' skill caps, there are two spells which they can't
ever write guaranteed: create familiar and charm monster. Create
familiar is a fairly niche spell (that doesn't match the Wizard
playstyle that well) and being unable to write it is not a major
problem. The inability to easily write charm monster is
intentional.

doc/fixes3-7-0.txt

@@ -1292,7 +1292,10 @@ if hero destroys a shop wall by breaking a wand of digging or applying a drum
 	of earthquake, have shopkeeper demand payment
 mimics sometimes woke up and came out of hiding when they shouldn't have if
 	hero without protection from shape changers returned to a previously
-	visitied level (though they would usually rehide so it wasn't obvious)
+	visited level (though they would usually rehide so it wasn't obvious)
+Wizards no longer have a bonus to writing unknown spellbooks, but now
+	learn what spellbooks look like as they gain skill in their
+	spell schools (allowing a guaranteed write with enough skill)
 
 
 Fixes to 3.7.0-x General Problems Exposed Via git Repository

include/extern.h

@@ -2760,6 +2760,7 @@ extern int known_spell(short);
 extern int spell_idx(short);
 extern char force_learn_spell(short);
 extern int num_spells(void);
+extern void skill_based_spellbook_id(void);
 
 /* ### steal.c ### */
 

src/spell.c

@@ -831,6 +831,40 @@ spell_skilltype(int booktype)
     return objects[booktype].oc_skill;
 }
 
+/* Wizards learn what spellbooks look like based on their skill in the
+   spell's school */
+void
+skill_based_spellbook_id(void)
+{
+    if (!Role_if(PM_WIZARD))
+        return;
+
+    int booktype;
+    const uchar spbook_class = (uchar) SPBOOK_CLASS;
+
+    for (booktype = gb.bases[spbook_class];
+         booktype < gb.bases[spbook_class + 1];
+         booktype++) {
+        int skill = spell_skilltype(booktype);
+        if (skill == P_NONE) continue;
+
+        int known_up_to_level;
+        switch (P_SKILL(skill)) {
+        case P_BASIC:
+            known_up_to_level = 2; break;
+        case P_SKILLED:
+            known_up_to_level = 4; break;
+        case P_EXPERT: case P_MASTER: case P_GRAND_MASTER:
+            known_up_to_level = 7; break;
+        case P_UNSKILLED: default:
+                known_up_to_level = 0; break;
+        }
+
+        if (objects[booktype].oc_level <= known_up_to_level)
+            makeknown(booktype);
+    }
+}
+
 static void
 cast_protection(void)
 {

src/weapon.c

@@ -1136,6 +1136,8 @@ skill_advance(int skill)
     You("are now %s skilled in %s.",
         P_SKILL(skill) >= P_MAX_SKILL(skill) ? "most" : "more",
         P_NAME(skill));
+
+    skill_based_spellbook_id();
 }
 
 static const struct skill_range {
@@ -1689,6 +1691,8 @@ skill_init(const struct def_skill *class_skill)
     /* each role has a special spell; allow at least basic for its type
        (despite the function name, this works for spell skills too) */
     unrestrict_weapon_skill(spell_skilltype(gu.urole.spelspec));
+
+    skill_based_spellbook_id();
 }
 
 void

src/write.c

@@ -313,8 +313,8 @@ dowrite(struct obj *pen)
     /*
      * Writing by name requires that the hero knows the scroll or
      * book type.  One has previously been read (and its effect
-     * was evident) or been ID'd via scroll/spell/throne and it
+     * was evident) or been ID'd via scroll/spell/throne (or skill
-     * will be on the discoveries list.
+     * for Wizards) and it will be on the discoveries list.
      * Unknown spellbooks can also be written by name if the hero
      * has fresh knowledge of the spell, or if the spell is almost
      * forgotten and the hero is Lucky (with a greater chance than
@@ -349,7 +349,8 @@ dowrite(struct obj *pen)
         /* else fresh knowledge of the spell works */
         && spell_knowledge != spe_Fresh
         /* and Luck might override after previous checks have failed */
-        && rnl((Role_if(PM_WIZARD) || spell_knowledge == spe_GoingStale)
+        && rnl(((Role_if(PM_WIZARD) && paper->oclass != SPBOOK_CLASS) ||
+                spell_knowledge == spe_GoingStale)
                ? 5 : 15)) {
         You("%s to write that.", by_descr ? "fail" : "don't know how");
         /* scrolls disappear, spellbooks don't */