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PHP: rfc:engine_warnings

 4 years ago
source link: https://wiki.php.net/rfc/engine_warnings
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Proposed Classification

The following table contains a list of errors with notice or warning severity generated in the engine, excluding warnings that are generated by functions which have an optimized opcode implementation.

The table shows both the current error level, as well as the proposed level. A rationale for the proposed change (or non-change) is provided below each group of errors.

The “undefined variable”, “undefined array index” and “division by zero” error conditions are discussed separately below, because they are more controversial.

Message Current Level Proposed Level
Attempt to increment/decrement property '%s' of non-object Warning Error exception
Attempt to modify property '%s' of non-object Warning Error exception
Attempt to assign property '%s' of non-object Warning Error exception
Creating default object from empty value Warning Error exception
Rationale: These errors are generated when a property is accessed on a non-object inside a write context. If the non-object is “truthy” a warning is generated and the operation is ignored, if it is “falsy” an empty stdClass object is created instead. While auto-vivification is a core part of the language for arrays, the same is not the case for objects, and creating a property on a non-object is almost certainly a programming error rather than an intentional action.
Trying to get property '%s' of non-object Notice Warning
Undefined property: %s::$%s Notice Warning
Rationale: The first warning is for the same case as above, but for read contexts. This is classified as a warning, because it usually indicates a programming error (in modern code, all non-magic properties tend to be known and fixed). However, object properties can also be dynamic (e.g. JSON in object form), in which case accessing an undefined property may be a less severe issue. Generally, PHP is somewhat lenient with read accesses to “missing” data.
Cannot add element to the array as the next element is already occupied Warning Error exception
Rationale: This error condition occurs when trying to push to an array for which the PHP_INT_MAX key is already used. This error condition practically never occurs outside of specially crafted code, and implies data loss if it does. As such, it is changed into an exception.
Cannot unset offset in a non-array variable Warning Error exception
Cannot use a scalar value as an array Warning Error exception
Trying to access array offset on value of type %s Notice Warning
Rationale: These diagnostics are generated when trying to use scalars as arrays. The first two occur in write contexts, the latter in read contexts. The latter was introduced in PHP 7.4 as a notice with express intention to elevate the severity in PHP 8.0. In line with the symmetrical case on objects, the write case is treated more severely here, as it usually implies data loss.
Only arrays and Traversables can be unpacked Warning TypeError exception
Invalid argument supplied for foreach() Warning TypeError exception
Rationale: These are simple type errors and should be treated as such.
Illegal offset type Warning TypeError exception
Illegal offset type in isset or empty Warning TypeError exception
Illegal offset type in unset Warning TypeError exception
Rationale: These are generated if an array or object is used as an array key. Once again this is a simple type error.
Indirect modification of overloaded element of %s has no effect Notice (Notice)
Indirect modification of overloaded property %s::$%s has no effect Notice (Notice)
Rationale: These notices occur if __get() or offsetGet() return a non-reference, but are used in a write context. Because our detection of write context has false positives right now, these should remain notices until we can be sure that the diagnostic is always legitimate.
Object of class %s could not be converted to int/float/number Notice (Notice)
Rationale: Comparison between objects and scalars currently works by casting the object to the appropriate type, which is why comparisons like $obj == 1 will currently also throw this notice, while they should not. Until this issue is resolved, the classification as notice should remain.
A non-numeric value encountered Warning (Warning)
A non well formed numeric value encountered Notice (Notice)
Rationale: The difference between these two warnings is whether a string is completely non-numeric, or whether it has a numeric prefix. This is a runtime issue based on the specific string value involved in an operation, which may be user-controlled. For this reason we don't promote to exceptions.
Accessing static property %s::$%s as non static Notice (Notice)
Rationale: This notice is somewhat confusing in what it does: It is thrown when accessing $obj->staticProp but does not actually read the static property. Instead it will fall back to using the dynamic property named staticProp. There is more inconsistency in this area, in that accessing a protected static property on the object will generate an Error exception, even though it would not actually access that property. I'm not sure what to do here, but would be inclined to just leave it alone.
Array to string conversion Notice Warning
Rationale: This is generally a bug (and the “Array” string you get is meaningless), but in many cases also not a particularly severe one. Since string conversion exceptions are supported now, we could also promote this to an Error exception, and I'm generally open to that.
Resource ID#%d used as offset, casting to integer (%d) Notice Warning
Rationale: This is in principle a meaningful operation, but exotic enough that intent should be indicated with an explicit integer cast.
String offset cast occurred Notice Warning
Illegal string offset '%s' Warning (Warning)
Rationale: The former is thrown when using null/bool/float as a string offset, the latter if the string is not integral. Both of these should use the same severity.
Uninitialized string offset: %d Notice Warning
Illegal string offset: %d Warning (Warning)
Rationale: The former is used when reading an out-of-bounds string offset, the latter when writing to an out-of-bounds negative string offset (for positive offsets, the string is extended instead). In line with undefined index/property, we consistently generate a warning here.
Cannot assign an empty string to a string offset Warning Error exception
Rationale: This operation is not meaningful and indicates some kind of logic error.
Only variables should be passed by reference Notice (Notice)
Only variable references should be returned by reference Notice (Notice)
Only variable references should be yielded by reference Notice (Notice)
Only variables should be assigned by reference Notice (Notice)
Attempting to set reference to non referenceable value Notice (Notice)
Cannot pass by-reference argument %d of %s%s%s() by unpacking a Traversable, passing by-value instead Warning (Warning)
Rationale: The use of values where a reference is expected is currently somewhat inconsistent, with everything from compiler errors, Error exceptions, warnings and notices being possible depending on the specific case. Passing a non-variable to a reference argument is often a programming error, because it will not be possible to modify the passed value and the reference cannot serve its purpose. However, this is complicated by optional reference arguments or return values that are optionally references. In both cases the warning may be a false positive. It's not really clear what to do here, so I'm retaining the current classification for now.

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