Stricter condition for type assignability

src/common/types/assign.ts

@@ -0,0 +1,93 @@
+import {
+    NeverType,
+    NonNeverType,
+    NumberPrimitive,
+    StringPrimitive,
+    Type,
+    UnionType,
+    intersect,
+    isDisjointWith,
+} from '@chainner/navi';
+
+export type AssignmentResult = AssignmentOk | AssignmentError;
+export interface AssignmentOk {
+    readonly isOk: true;
+    readonly assignedType: NonNeverType;
+}
+export interface AssignmentError {
+    readonly isOk: false;
+    readonly assignedType: NeverType;
+    readonly errorType: Type;
+}
+
+/**
+ * We only want to split if there is at least one specific struct instance or there are no struct instances at all.
+ */
+const shouldSplit = (items: readonly Type[]): boolean => {
+    let noStructs = true;
+    for (const item of items) {
+        if (item.underlying === 'struct') {
+            noStructs = false;
+            if (item.type === 'instance') {
+                return true;
+            }
+        }
+    }
+    return noStructs;
+};
+const splitType = (t: Type): Type[] => {
+    if (t.underlying === 'union' && shouldSplit(t.items)) {
+        const numbers: NumberPrimitive[] = [];
+        const strings: StringPrimitive[] = [];
+        const result: Type[] = [];
+        for (const item of t.items) {
+            if (item.underlying === 'number') {
+                numbers.push(item);
+            } else if (item.underlying === 'string') {
+                strings.push(item);
+            } else {
+                result.push(item);
+            }
+        }
+
+        if (numbers.length === 1) {
+            result.push(numbers[0]);
+        } else if (numbers.length >= 2) {
+            result.push(new UnionType(numbers as never));
+        }
+        if (strings.length === 1) {
+            result.push(strings[0]);
+        } else if (strings.length >= 2) {
+            result.push(new UnionType(strings as never));
+        }
+        return result;
+    }
+    return [t];
+};
+
+/**
+ * Returns whether the type `t` can be assigned to an input of type `definitionType`.
+ */
+export const assign = (t: Type, definitionType: Type): AssignmentResult => {
+    const split = splitType(t);
+    if (split.length > 1) {
+        for (const item of split) {
+            if (isDisjointWith(item, definitionType)) {
+                return { isOk: false, assignedType: NeverType.instance, errorType: item };
+            }
+        }
+    }
+
+    const intersection = intersect(t, definitionType);
+    if (intersection.underlying === 'never') {
+        return { isOk: false, assignedType: intersection, errorType: t };
+    }
+    return { isOk: true, assignedType: intersection };
+};
+
+/**
+ * Equivalent to `assign(t, definitionType).isOk`, but faster.
+ */
+export const assignOk = (t: Type, definitionType: Type): boolean => {
+    return assign(t, definitionType).isOk;
+};

src/common/types/function.ts

@@ -12,13 +12,13 @@ import {
     evaluate,
     getReferences,
     intersect,
-    isDisjointWith,
     literal,
     union,
     without,
 } from '@chainner/navi';
 import { Input, InputId, InputSchemaValue, NodeSchema, Output, OutputId } from '../common-types';
 import { EMPTY_MAP, assertNever, lazy, lazyKeyed, topologicalSort } from '../util';
+import { assign, assignOk } from './assign';
 import { getChainnerScope } from './chainner-scope';
 import { fromJson } from './json';
 import type { PassthroughInfo } from '../PassthroughMap';
@@ -454,7 +454,7 @@ export class FunctionDefinition {
         this.inputConvertibleDefaults = new Map(
             [...this.inputDefaults].map(([id, d]) => {
                 const c = this.inputConversions.get(id)?.convertibleTypes ?? NeverType.instance;
-                return [id, union(d, c)];
+                return [id, union(d, c)] as const;
             })
         );
 
@@ -492,11 +492,11 @@ export class FunctionDefinition {
     }
 
     canAssignInput(inputId: InputId, type: Type): boolean {
-        const inputType = this.inputDefaults.get(inputId);
-        if (!inputType) {
+        const definitionType = this.inputDefaults.get(inputId);
+        if (!definitionType) {
             throw new Error('Invalid input id');
         }
-        return !isDisjointWith(inputType, this.convertInput(inputId, type));
+        return assignOk(this.convertInput(inputId, type), definitionType);
     }
 
     hasInput(inputId: InputId): boolean {
@@ -581,7 +581,7 @@ export class FunctionInstance {
                 const assignedType = partialInputs(id);
                 if (assignedType) {
                     const converted = definition.convertInput(id, assignedType);
-                    const newType = intersect(converted, type);
+                    const newType = assign(converted, type).assignedType;
                     if (newType.type === 'never') {
                         inputErrors.push({ inputId: id, inputType: type, assignedType });
                     }
@@ -666,10 +666,10 @@ export class FunctionInstance {
     }
 
     canAssign(inputId: InputId, type: Type): boolean {
-        const iType = this.definition.inputDefaults.get(inputId);
-        if (!iType) throw new Error(`Invalid input id ${inputId}`);
+        const definitionType = this.definition.inputDefaults.get(inputId);
+        if (!definitionType) throw new Error(`Invalid input id ${inputId}`);
 
         // we say that types A is assignable to type B if they are not disjoint
-        return !isDisjointWith(iType, this.definition.convertInput(inputId, type));
+        return assignOk(this.definition.convertInput(inputId, type), definitionType);
     }
 }

src/common/types/mismatch.ts

@@ -8,6 +8,7 @@ import {
     isStructInstance,
 } from '@chainner/navi';
 import { assertNever } from '../util';
+import { assign } from './assign';
 import { getChainnerScope } from './chainner-scope';
 import { explain, formatChannelNumber } from './explain';
 import { prettyPrintType } from './pretty';
@@ -31,11 +32,15 @@ export const generateAssignmentErrorTrace = (
     assigned: Type,
     definition: Type
 ): AssignmentErrorTrace | undefined => {
-    if (!isDisjointWith(assigned, definition)) {
+    const assignmentResult = assign(assigned, definition);
+    if (assignmentResult.isOk) {
         // types compatible
         return undefined;
     }
 
+    // eslint-disable-next-line no-param-reassign
+    assigned = assignmentResult.errorType;
+
     if (
         isStructInstance(assigned) &&
         isStructInstance(definition) &&