[WIP] Prevent land-derived speeds from receiving bonuses twice from same source

src/module/actor/creature/document.ts

@@ -748,7 +748,7 @@ abstract class CreaturePF2e<
                     domain["derived-from-land"] = true;
                 }
                 const statistic = selected.derivedFromLand
-                    ? landSpeed.extend({ type, base: selected.value, source: selected.source })
+                    ? landSpeed.extend({ type, base: selected.value, source: selected.source, derivedFromLand: true })
                     : new SpeedStatistic(this, {
                           type,
                           base: selected.value,

src/module/rules/rule-element/base-speed.ts

@@ -53,9 +53,14 @@ class BaseSpeedRuleElement extends RuleElement<BaseSpeedRuleSchema> {
                 if (!Number.isInteger(value)) this.failValidation("Failed to resolve value");
                 return null;
             }
-            // Whether this speed is derived from the creature's land speed
+            const landTotal = this.actor.system.movement?.speeds?.land?.value ?? 0;
+            // Whether this speed is derived from the land speed.
+            // If choices are between constant and land speed, only true if land speed was chosen.
             const derivedFromLand =
-                type !== "land" && typeof this.value === "string" && this.value.includes("movement.speeds.land.value");
+                type !== "land" &&
+                typeof this.value === "string" &&
+                this.value.includes("movement.speeds.land.value") &&
+                value === landTotal;
             return { type: type, value, source: this.getReducedLabel(), derivedFromLand };
         };
     }

src/module/rules/rule-element/flat-modifier.ts

@@ -1,5 +1,6 @@
 import { DeferredValueParams, MODIFIER_TYPES, Modifier, ModifierType } from "@actor/modifiers.ts";
 import { AttributeString } from "@actor/types.ts";
+import { MOVEMENT_TYPES } from "@actor/values.ts";
 import { damageCategoriesUnique } from "@scripts/config/damage.ts";
 import { DamageCategoryUnique } from "@system/damage/types.ts";
 import {
@@ -129,6 +130,21 @@ class FlatModifierRuleElement extends RuleElement<FlatModifierSchema> {
             if (selector === "null") continue;
 
             const construct = (options: DeferredValueParams = {}): Modifier | null => {
+                // If same rule affects land- and another speed: omit non-land modifier when base is land-derived.
+                const testRollOptions = options.test ?? [];
+                const derivedFromLand = Array.isArray(testRollOptions)
+                    ? testRollOptions.includes("derived-from-land")
+                    : testRollOptions.has("derived-from-land");
+                if (
+                    selectors.includes("land-speed") &&
+                    selector !== "land-speed" &&
+                    selector.endsWith("-speed") &&
+                    MOVEMENT_TYPES.includes(selector.replace(/-speed$/, "") as never) &&
+                    derivedFromLand
+                ) {
+                    return null;
+                }
+
                 const resolvedValue = Number(this.resolveValue(this.value, 0, options)) || 0;
                 if (this.ignored) return null;
 

src/module/system/statistic/speed.ts

@@ -4,7 +4,7 @@ import { MovementType } from "@actor/types.ts";
 import { extractModifierAdjustments, extractModifiers } from "@module/rules/helpers.ts";
 import { ErrorPF2e, localizer } from "@util";
 import { BaseStatistic } from "./base.ts";
-import { BaseStatisticData, BaseStatisticTraceData } from "./data.ts";
+import { BaseStatisticData, BaseStatisticTraceData, StatisticData } from "./data.ts";
 
 class SpeedStatistic<TActor extends ActorPF2e, TType extends MovementType | "travel"> extends BaseStatistic<TActor> {
     constructor(actor: TActor, options: SpeedStatisticData<TType>) {
@@ -30,6 +30,15 @@ class SpeedStatistic<TActor extends ActorPF2e, TType extends MovementType | "tra
         this.modifiers = [...syntheticModifiers, ...additionalModifiers];
     }
 
+    /** Roll options for this speed, including {@link SpeedStatisticData.derivedFromLand} when applicable. */
+    override createRollOptions(domains = this.domains): Set<string> {
+        const set = super.createRollOptions(domains);
+        if ((this.data as StatisticData & { derivedFromLand?: boolean }).derivedFromLand) {
+            set.add("derived-from-land");
+        }
+        return set;
+    }
+
     /** The movement type for this statistic */
     type: TType;
 
@@ -64,8 +73,15 @@ class SpeedStatistic<TActor extends ActorPF2e, TType extends MovementType | "tra
 
     /** Derive a travel speed from this statistic. */
     extend<TType extends MovementType | "travel">(options: ExtendParams<TType>): SpeedStatistic<TActor, TType> {
-        const { type, base = this.value, modifiers = [], source = this.source } = options;
-        return new SpeedStatistic(this.actor, { type, base, modifiers, domains: [`${type}-speed`], source });
+        const { type, base = this.value, modifiers = [], source = this.source, derivedFromLand } = options;
+        return new SpeedStatistic(this.actor, {
+            type,
+            base,
+            modifiers,
+            domains: [`${type}-speed`],
+            source,
+            derivedFromLand,
+        });
     }
 
     override getTraceData(): TType extends "land"
@@ -97,6 +113,8 @@ interface SpeedStatisticData<TType extends MovementType | "travel"> extends Omit
     base?: number;
     /** A feature, ancestry, effect, etc. from which this speed originated */
     source?: string | null;
+    /** Is this speed based from land; used to prevent double-application of modifiers. */
+    derivedFromLand?: boolean;
 }
 
 interface SpeedStatisticTraceData<
@@ -115,7 +133,7 @@ interface LandSpeedStatisticTraceData extends SpeedStatisticTraceData<"land"> {
 
 interface ExtendParams<TType extends MovementType | "travel"> extends Pick<
     SpeedStatisticData<TType>,
-    "type" | "base" | "modifiers" | "source"
+    "type" | "base" | "modifiers" | "source" | "derivedFromLand"
 > {}
 
 export { SpeedStatistic };