Add valueStringifier for reporting

README.md

@@ -230,6 +230,12 @@ pass a `DetailedSpec` object that has the following fields:
   An object that maps from `NODE_ENV` values to values that will be passed as
   input to the schema if this var isn't present in the environment. For example:
 
+- `valueStringifier?: (value: string | TIn) => string`
+
+  A function that takes the received value (as a string) or the default value
+  (as `TIn`, the expected type after parsing) and returns the string that
+  should be displayed in the error report. 
+
   ```ts
   const schemas = {
     FRUIT: {

src/parse-env.ts

@@ -41,6 +41,18 @@ export type DetailedSpec<
        * (For example, `z.number().gte(20).default(50)`.)
        */
       defaults?: Record<string, TIn | undefined>;
+
+      /**
+       * A function that takes the received value (as a string) or the default
+       * value (as `TIn`, the expected type after parsing) and returns the string
+       * that should be displayed in the error report.
+       *
+       * This can be used, for example, to redact sensitive values from error
+       * reports.
+       *
+       * For example, `(value: string) => value.replace(/./g, '*')`.
+       */
+       valueStringifier?: (value: string | TIn) => string;
     }
   : never;
 

src/reporter.ts

@@ -1,6 +1,6 @@
 import { ZodError, ZodErrorMap, ZodIssueCode } from "zod";
 import { yellow, red, cyan, green } from "colorette";
-import { Schemas } from "./parse-env.js";
+import { DetailedSpec, Schemas } from "./parse-env.js";
 
 // Even though we also have our own formatter, we pass a custom error map to
 // Zod's `.parse()` for two reasons:
@@ -34,6 +34,7 @@ export function reportErrors(
   const formattedErrors = errors.map(
     ({ key, receivedValue, error, defaultUsed, defaultValue }) => {
       const message: string[] = [`[${yellow(key)}]:`];
+      const valueStringifier = (schemas[key] as DetailedSpec).valueStringifier ?? JSON.stringify;
 
       if (error instanceof ZodError) {
         const { formErrors, fieldErrors } = error.flatten();
@@ -61,7 +62,7 @@ export function reportErrors(
           `(received ${cyan(
             receivedValue === undefined
               ? "undefined"
-              : JSON.stringify(receivedValue),
+              : valueStringifier(receivedValue)
           )})`,
           2,
         ),
@@ -73,7 +74,7 @@ export function reportErrors(
             `(used default of ${cyan(
               defaultValue === undefined
                 ? "undefined"
-                : JSON.stringify(defaultValue),
+                : valueStringifier(defaultValue)
             )})`,
             2,
           ),