Convert null types to nullable for better errors

Author: SamyPesse

src/compileValueSchema.ts

@@ -35,7 +35,10 @@ function createSafeLiteral(
 /**
  * Compile a JSON schema into a validation function.
  */
-export function compileValueSchema(compiler: Compiler, schema: OpenAPIValueSchema) {
+export function compileValueSchema(
+    compiler: Compiler,
+    schema: OpenAPIValueSchema,
+): namedTypes.Identifier {
     if ('$ref' in schema) {
         return compileValueSchema(compiler, compiler.resolveRef(schema));
     }
@@ -108,13 +111,29 @@ function compileNullTypeSchema(compiler: Compiler, schema: object) {
 
 /**
  * OpenAPI 3.1: type as array, e.g. type: ['string', 'null']
- * Converts to an anyOf schema internally.
+ * Converts nullable two-type unions to the existing nullable fast-path.
+ * Other unions are still compiled as anyOf.
  */
-function compileTypeArraySchema(compiler: Compiler, schema: OpenAPITypeArraySchema) {
+function compileTypeArraySchema(
+    compiler: Compiler,
+    schema: OpenAPITypeArraySchema,
+): namedTypes.Identifier {
     const { type, ...rest } = schema;
 
-    const typesWithoutNull = type.filter((t) => t !== 'null');
-    const hasNull = type.includes('null');
+    type OpenAPINonNullType = Exclude<OpenAPITypeArraySchema['type'][number], 'null'>;
+
+    const typesWithoutNull = type.filter((t): t is OpenAPINonNullType => t !== 'null');
+    const hasNull = typesWithoutNull.length !== type.length;
+
+    if (hasNull && type.length === 2 && typesWithoutNull.length === 1) {
+        const [nonNullType] = typesWithoutNull;
+
+        return compileValueSchema(compiler, {
+            ...rest,
+            type: nonNullType,
+            nullable: true,
+        } as OpenAPIValueSchema);
+    }
 
     const anyOf: OpenAPIValueSchema[] = typesWithoutNull.map(
         (t) => ({ ...rest, type: t }) as OpenAPIValueSchema,

src/tests/__snapshots__/compileValueSchema.test.ts.snap

@@ -1889,28 +1889,14 @@ export class ValidationError extends RequestError {
         this.path = path;
     }
 }
-function obj1(path, value, context) {
+function obj0(path, value, context) {
+    if (value === null) {
+        return value;
+    }
     if (typeof value !== 'string') {
         return new ValidationError(path, 'expected a string');
     }
     return value;
-}
-function obj2(path, value, context) {
-    if (value !== null) {
-        return new ValidationError(path, 'expected null');
-    }
-    return value;
-}
-function obj0(path, value, context) {
-    const value0 = obj1(path, value, context);
-    if (!(value0 instanceof ValidationError)) {
-        return value0;
-    }
-    const value1 = obj2(path, value, context);
-    if (!(value1 instanceof ValidationError)) {
-        return value1;
-    }
-    return new ValidationError(path, 'expected one of the anyOf schemas to match');
 }"
 `;
 
@@ -2008,30 +1994,16 @@ export class ValidationError extends RequestError {
         this.path = path;
     }
 }
-function obj1(path, value, context) {
+function obj0(path, value, context) {
+    if (value === null) {
+        return value;
+    }
     if (typeof value !== 'string') {
         return new ValidationError(path, 'expected a string');
     }
     if (value.length < 1) {
         return new ValidationError(path, 'expected at least 1 characters');
     }
     return value;
-}
-function obj2(path, value, context) {
-    if (value !== null) {
-        return new ValidationError(path, 'expected null');
-    }
-    return value;
-}
-function obj0(path, value, context) {
-    const value0 = obj1(path, value, context);
-    if (!(value0 instanceof ValidationError)) {
-        return value0;
-    }
-    const value1 = obj2(path, value, context);
-    if (!(value1 instanceof ValidationError)) {
-        return value1;
-    }
-    return new ValidationError(path, 'expected one of the anyOf schemas to match');
 }"
 `;