Exception message is not on point for unary operator

[mvorisek]

Description

The following code:

var_dump(- '3');
$v = 'x';
var_dump(- $v);
var_dump(- 'x');

https://3v4l.org/tokuW

it seems the exception message does not expect unary operator, as for 1 + 'x' it makes much more sense and the operator is displayed correctly

Resulted in this output:

int(-3)

Fatal error: Uncaught TypeError: Unsupported operand types: string * int in /in/tokuW:5
Stack trace:
#0 {main}
  thrown in /in/tokuW on line 5

But I expected this output instead:

int(-3)
1x meaningful exception (or 2x warning)

PHP Version

PHP 8.0+

Operating System

any

[mvorisek]

also https://3v4l.org/hjmcJ should emit an error as the whole string was not consumed

[cmb69]

That TypeError message is because unary minus is actually implemented as multiplication with -1. I'm not sure if it is worth fixing the message.

[mvorisek]

I did some investigation:

1. I would expect substracting from zero instead of multiplication by minus one [1]
2. at least in C# [2] unary operators are natively supported, so they should be supported in PHP as well

both points are important if a custom operators are to be supported (officially or by a custom ext)

[1] https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/language-specification/expressions#1183-unary-minus-operator
[2] https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/operator-overloading

given the unary operator should be supported by design, I would expect

-TypeError: Unsupported operand types: string * int
+TypeError: Unsupported operand types: - string

exception message

[damianwadley]

It's kind of weird, at least to me as an outsider to this stuff, to see zend_ast create 0-$v while zend_compile does $v*-1.
https://github.com/php/php-src/blob/php-8.1.12/Zend/zend_ast.c#L662-L670
https://github.com/php/php-src/blob/php-8.1.12/Zend/zend_compile.c#L8717-L8737

2. at least in C# [2] unary operators are natively supported, so they should be supported in PHP as well

This is a unary operator. It is natively supported here...

[cmb69]

It's kind of weird, at least to me as an outsider to this stuff, to see zend_ast create 0-$v while zend_compile does $v*-1.

Oh, wow!

The "problem" with the 0-num approach is the "unexpected" result for float(0), which would be 0, instead of the expected float(-0). See https://bugs.php.net/52355. However, the fix made var_dump(0 - (0.0)); // float(0) inconsistent.

And apparently, the AST creation has been overlooked.

[iluuu1994]

It's kind of weird, at least to me as an outsider to this stuff, to see zend_ast create 0-$v while zend_compile does $v*-1.

Nice catch! I created a PR for this.

#10978

As for the rest, I don't think it makes sense atm. We don't have operator overloading (apart from extensions). Extensions should also have no other choice but to handle -$x and $x * -1 as equivalent. Adding separate opcodes and handlers, complicating the optimizer and so forth doesn't seem worth it. Sorry.

[mvorisek]

@iluuu1994 can you please reopen this issue as it is for a message inconsistency which is still present.

[KapitanOczywisty]

@mvorisek It's "won't fix", so should stay closed, unless you found something else, then open a new issue.