Why is Composer issuing PSR-4 autoloading deprecation warnings about class path mismatches?

Composer PSR-4 Autoloading Deprecation: Class Path Mismatch

When executing composer commands like update and install, you may encounter a deprecation notice regarding a class that does not comply with the PSR-4 autoloading standard. This typically occurs when there is a discrepancy between the class's fully qualified name and the path of its corresponding file.

Path Case

The most common cause is a mismatch in the case of the pathname components and the class name. For instance, "foo/bar/Baz.php" does not correspond to "FooBarBaz." Ensure that the case of each pathname component matches the case of the namespace it represents, such as "Foo/Bar/Baz.php" for "FooBarBaz". Condition. Sometimes, your class (or namespace) may be named FooBar, but its disk path is "foo-bar". This situation also triggers a warning. You need to rename the file or class (or namespace).

Often changing a path or file is easier than changing a class or namespace name because changing a class or namespace name requires you to refactor your code to match the new name, whereas changing a path doesn't require refactoring anything content.

Nested namespaces and missing declarations

Suppose you have:

and class Dummy is defined in src/Buzz:

The above code works fine but will throw warnings similar to other situations. The correct approach should be:

"autoload": {
    "psr-4": {
        "Fizz\Buzz\": "src/"
    }
}

You need to make changes not only to the affected class, but also to any other files that use or import that class (for example, by now declaring use FizzBuzzBuzzDummy;) .

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