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Enhance logger function typing #2230

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Merged
mcollina merged 8 commits into from
Jun 15, 2025
Merged

Enhance logger function typing #2230

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6f9dd3b
Enhance logger function typing
samchungy Jun 11, 2025
15d0ee7
Update pino.test-d.ts
samchungy Jun 11, 2025
bd993c7
Adjust naming
samchungy Jun 11, 2025
84c6e1d
Allow missing template specifiers
samchungy Jun 11, 2025
d492f41
rename to placeholder
samchungy Jun 11, 2025
ac10024
drop redundant unknown
samchungy Jun 12, 2025
5acfefc
Switch to unknown
samchungy Jun 12, 2025
87d1e2e
address edge-case
samchungy Jun 12, 2025
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26 changes: 20 additions & 6 deletions pino.d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -319,12 +319,27 @@ declare namespace pino {
labels: { [level: number]: string };
}

type PlaceholderSpecifier = 'd' | 's' | 'j' | 'o' | 'O';
type PlaceholderTypeMapping<T extends PlaceholderSpecifier> = T extends 'd'
? number
: T extends 's'
? string
: T extends 'j' | 'o' | 'O'
? object
: never;

type ParseLogFnArgs<
T,
Acc extends unknown[] = [],
> = T extends `${infer _}%${infer Placeholder}${infer Rest}`
? Placeholder extends PlaceholderSpecifier
? ParseLogFnArgs<Rest, [...Acc, PlaceholderTypeMapping<Placeholder>]>
: ParseLogFnArgs<Rest, Acc>
: Acc;

interface LogFn {
// TODO: why is this different from `obj: object` or `obj: any`?
/* tslint:disable:no-unnecessary-generics */
<T extends object>(obj: T, msg?: string, ...args: any[]): void;
(obj: unknown, msg?: string, ...args: any[]): void;
(msg: string, ...args: any[]): void;
<T, TMsg extends string = string>(obj: T, msg?: T extends string ? never: TMsg, ...args: ParseLogFnArgs<TMsg> | []): void;
<_, TMsg extends string = string>(msg: TMsg, ...args: ParseLogFnArgs<TMsg> | []): void;
}

interface LoggerOptions<CustomLevels extends string = never, UseOnlyCustomLevels extends boolean = boolean> {
Expand Down Expand Up @@ -886,4 +901,3 @@ export { pino as default, pino };
// `import {P} from "pino"; const log: P.Logger;`.
// (Legacy support for early 7.x releases, remove in 8.x.)
export type { pino as P };

55 changes: 54 additions & 1 deletion test/types/pino.test-d.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -10,10 +10,63 @@ const error = log.error;

info("hello world");
error("this is at error level");
info("the answer is %d", 42);

// primative types
info('simple string');
info(true)
info(42);
info(3.14);
info(null);
info(undefined);

// object types
info({ a: 1, b: '2' });
info(new Error());
info(new Date());
info([])
info(new Map());
info(new Set());

// placeholder messages
info('Hello %s', 'world');
info('The answer is %d', 42);
info('The object is %o', { a: 1, b: '2' });
info('The json is %j', { a: 1, b: '2' });
info('The object is %O', { a: 1, b: '2' });
info('The answer is %d and the question is %s with %o', 42, 'unknown', { correct: 'order' });
info('Missing placeholder is fine %s');
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@samchungy samchungy Jun 11, 2025 •
edited
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I've allowed strings with missing placeholder data but if we want to be more strict and require that they add them we can just change the type of args from ...args: ParseLogFnArgs<TMsg> | [] to ...args: ParseLogFnArgs<TMsg> .

But, this is technically valid

declare const errorOrString: string | Error;
info(errorOrString)

// placeholder messages type errors
expectError(info('Hello %s', 123));
expectError(info('Hello %s', false));
expectError(info('The answer is %d', 'not a number'));
expectError(info('The object is %o', 'not an object'));
expectError(info('The object is %j', 'not a JSON'));
expectError(info('The object is %O', 'not an object'));
expectError(info('The answer is %d and the question is %s with %o', 42, { incorrect: 'order' }, 'unknown'));
expectError(info('Extra message %s', 'after placeholder', 'not allowed'));

// object types with messages
info({ obj: 42 }, "hello world");
info({ obj: 42, b: 2 }, "hello world");
info({ obj: { aa: "bbb" } }, "another");
info({ a: 1, b: '2' }, 'hello world with %s', 'extra data');

// Extra message after placeholder
expectError(info({ a: 1, b: '2' }, 'hello world with %d', 2, 'extra' ));

// metadata with messages type errors
expectError(info({ a: 1, b: '2' }, 'hello world with %s', 123));

// metadata after message
expectError(info('message', { a: 1, b: '2' }));

// multiple strings without placeholder
expectError(info('string1', 'string2'));
expectError(info('string1', 'string2', 'string3'));

setImmediate(info, "after setImmediate");
error(new Error("an error"));

Expand Down