Type inferring is incorrect on `@template K of array-key`, yet it is correct for (almost) the same code with `@template T`

[gnutix]

Bug report

Hello there. While adding some types and types' tests for a bunch of Functional-related functions in our codebase, I noticed some weird behavior.

I have two functions :

1. find(array $array, mixed $value): mixed (|null being implied)
2. findKey(array $array, int|string $key): int|string|null

The implementation is strictly the same (as far as PHP code is concerned), yet the produced types are wildly different. I guess it's because of array-key and how it is processed ?

(I don't currently have the time to work on an implementation, but maybe someone will.)

Code snippet that reproduces the problem

https://phpstan.org/r/d979d850-c552-4598-bb72-50ee7cf7d4eb

Expected output

The above code sample should produce the expected types.

Did PHPStan help you today? Did it make you happy in any way?

(I have a bunch of small issues to create, sorry if I don't come up with something new for each of them 🙏 )

[phpstan-bot]

@gnutix After the latest push in 2.0.x, PHPStan now reports different result with your code snippet:

@@ @@
 84: Expected type int|null, actual: int|string|null
 85: Expected type 'work'|null, actual: int|string|null
 
-PHP 7.1 – 7.4 (6 errors)
+PHP 7.1 – 7.4 (23 errors)
 ==========
 
+20: Function find() has invalid return type mixed.
+20: PHPDoc tag @return with type ($array is array ? T|null : null) is not subtype of native type mixed.
+24: Function find() should return mixed but returns T.
+28: Function find() should return mixed but returns null.
+40: Function findKey() has invalid return type null.
+40: Function findKey() never returns null so it can be removed from the return type.
 40: Function findKey() uses native union types but they're supported only on PHP 8.0 and later.
-78: Expected type null, actual: int|string|null
-81: Expected type int|null, actual: int|string|null
-82: Expected type 'id'|'name'|null, actual: int|string|null
-84: Expected type int|null, actual: int|string|null
-85: Expected type 'work'|null, actual: int|string|null
+40: PHPDoc tag @return with type ($array is array ? int|string|null : null) is not subtype of native type int|null|string.
+48: Function findKey() should return int|null|string but returns null.
+65: Expected type null, actual: mixed|null
+66: Expected type null, actual: mixed|null
+67: Expected type null, actual: mixed|null
+69: Expected type string|null, actual: mixed|null
+70: Expected type int|string|null, actual: mixed|null
+72: Expected type Timeline<Percentage>|null, actual: mixed|null
+73: Expected type Timeline<Percentage>|null, actual: mixed|null
+77: Expected type null, actual: null#1|null#2
+78: Expected type null, actual: int|null#1|string|null#2
+79: Expected type null, actual: null#1|null#2
+81: Expected type int|null, actual: int|null#1|string|null#2
+82: Expected type 'id'|'name'|null, actual: int|null#1|string|null#2
+84: Expected type int|null, actual: int|null#1|string|null#2
+85: Expected type 'work'|null, actual: int|null#1|string|null#2

Full report

PHP 8.0 – 8.1 (5 errors)

Line	Error
78	`Expected type null, actual: int
81	`Expected type int
82	`Expected type 'id'
84	`Expected type int
85	`Expected type 'work'

PHP 7.1 – 7.4 (23 errors)

Line	Error
20	Function find() has invalid return type mixed.
20	`PHPDoc tag @return with type ($array is array ? T
24	Function find() should return mixed but returns T.
28	Function find() should return mixed but returns null.
40	Function findKey() has invalid return type null.
40	Function findKey() never returns null so it can be removed from the return type.
40	Function findKey() uses native union types but they're supported only on PHP 8.0 and later.
40	`PHPDoc tag @return with type ($array is array ? int
48	`Function findKey() should return int
65	`Expected type null, actual: mixed
66	`Expected type null, actual: mixed
67	`Expected type null, actual: mixed
69	`Expected type string
70	`Expected type int
72	`Expected type Timeline
73	`Expected type Timeline
77	`Expected type null, actual: null#1
78	`Expected type null, actual: int
79	`Expected type null, actual: null#1
81	`Expected type int
82	`Expected type 'id'
84	`Expected type int
85	`Expected type 'work'

[phpstan-bot]

@gnutix After the latest push in 2.1.x, PHPStan now reports different result with your code snippet:

@@ @@
 84: Expected type int|null, actual: int|string|null
 85: Expected type 'work'|null, actual: int|string|null
 
-PHP 7.1 – 7.4 (6 errors)
+PHP 7.1 – 7.4 (22 errors)
 ==========
 
+20: Function find() has invalid return type mixed.
+20: PHPDoc tag @return with type ($array is array ? T|null : null) is not subtype of native type mixed.
+24: Function find() should return mixed but returns T.
+28: Function find() should return mixed but returns null.
+40: Function findKey() has invalid return type null.
 40: Function findKey() uses native union types but they're supported only on PHP 8.0 and later.
-78: Expected type null, actual: int|string|null
-81: Expected type int|null, actual: int|string|null
-82: Expected type 'id'|'name'|null, actual: int|string|null
-84: Expected type int|null, actual: int|string|null
-85: Expected type 'work'|null, actual: int|string|null
+40: PHPDoc tag @return with type ($array is array ? int|string|null : null) is not subtype of native type int|null|string.
+48: Function findKey() should return int|null|string but returns null.
+65: Expected type null, actual: mixed|null
+66: Expected type null, actual: mixed|null
+67: Expected type null, actual: mixed|null
+69: Expected type string|null, actual: mixed|null
+70: Expected type int|string|null, actual: mixed|null
+72: Expected type Timeline<Percentage>|null, actual: mixed|null
+73: Expected type Timeline<Percentage>|null, actual: mixed|null
+77: Expected type null, actual: null#1|null#2
+78: Expected type null, actual: int|null#1|string|null#2
+79: Expected type null, actual: null#1|null#2
+81: Expected type int|null, actual: int|null#1|string|null#2
+82: Expected type 'id'|'name'|null, actual: int|null#1|string|null#2
+84: Expected type int|null, actual: int|null#1|string|null#2
+85: Expected type 'work'|null, actual: int|null#1|string|null#2

Full report

PHP 8.0 – 8.1 (5 errors)

Line	Error
78	`Expected type null, actual: int
81	`Expected type int
82	`Expected type 'id'
84	`Expected type int
85	`Expected type 'work'

PHP 7.1 – 7.4 (22 errors)

Line	Error
20	Function find() has invalid return type mixed.
20	`PHPDoc tag @return with type ($array is array ? T
24	Function find() should return mixed but returns T.
28	Function find() should return mixed but returns null.
40	Function findKey() has invalid return type null.
40	Function findKey() uses native union types but they're supported only on PHP 8.0 and later.
40	`PHPDoc tag @return with type ($array is array ? int
48	`Function findKey() should return int
65	`Expected type null, actual: mixed
66	`Expected type null, actual: mixed
67	`Expected type null, actual: mixed
69	`Expected type string
70	`Expected type int
72	`Expected type Timeline
73	`Expected type Timeline
77	`Expected type null, actual: null#1
78	`Expected type null, actual: int
79	`Expected type null, actual: null#1
81	`Expected type int
82	`Expected type 'id'
84	`Expected type int
85	`Expected type 'work'

[phpstan-bot]

Closed via merging phpstan/phpstan-src#6376