[4.0] Support string literals

[ruudk]

After posting this as an idea in #3951 (comment) I tried to implement it. It looks like it's quite doable. But maybe I'm missing something.

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This allows to write a string literal using backticks. When using a literal, you don't need to escape backslashes. This is ideal for situation where you want to reference a fully qualified class name. For example in a constant function.

For example, before you had to write:

{{ constant("App\\Entity\\Class::Constant") }}

Now you can write:

{{ constant(`App\Entity\Class::Constant`) }}

Besides easier to read, there is another huge benefit: when doing a text search for a fully qualified class name, it will show up.

[smnandre]

To clarify the terminology and avoid any misunderstandings in this conversation:

Twig already supports string literals, as 'foo' and "foo" are both already... string literals. To be precise they are quoted sequence of characters using single or double-quote paired delimiters, using \\ as escaping prefix.

What you suggest here is about introducing another syntax of string literals: with ` as delimiter (and still \ as escaping prefix, but without the need to escape... itself).

In the Javascript world, the backtick is used in template literals, offering two things harder to do without:

• multi-lines strings
• string interpolation

These two points do not offer significant advantages for Twig, as it already provides mechanisms for these needs.

Therefore, I am not entirely convinced that the advantages (facilitating PHP execution in very specific cases) outweigh the costs (significant changes to the Lexer, increased maintenance, and additional documentation).

But maybe there are other features/benefits i don't see here?

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PhpStorm already does offer support for the constant function in Twig, i'm sure if it does not support Enum yet, it will be done soon. And i guess similar plugin can be found for alternative IDEs.

[ruudk]

Regarding the PHPStorm screenshot: is that native or via that Symfony plugin?

[smnandre]

Regarding the PHPStorm screenshot: is that native or via that Symfony plugin?

Via the Symfony plugin it seems (found this PR that seems very related to the current PR : Haehnchen/idea-php-symfony2-plugin@b358ff0 )

[stof]

There was a discussion in the past about adding support for unescaped slashes in existing string literals (keeping the option to escape them as well), by producing a deprecation warning for any useless escaping in strings (\d in a Twig string currently means d as unknown escape sequence is treated as resolving to the unescaped character).
This would allow to avoid escaping the \ except when the following character has a meaning in an escape sequence, like the way double-quoted string literals work in PHP (see https://3v4l.org/A2mPT).

Implementing this involves replacing stripcslashes by an implementation distinguishing useless escaping in

Twig/src/Lexer.php

Line 370 in 6b6aca5

$this->pushToken(/* Token::STRING_TYPE */ 7, stripcslashes(substr($match[0], 1, -1)));

If this gets implemented, we might not need to introduce a third syntax for string literals in Twig.

[smnandre]

If this gets implemented, we might not need to introduce a third syntax for string literals in Twig.

But to get there you'd have to change the string regexp no ?

Edit: nope, that works

https://3v4l.org/RfnYM

[fabpot]

I agree with @stof suggestion.

[ruudk]

Should I try a PR for that?

[fabpot]

Should I try a PR for that?

That would be great!

[ruudk]

Created a PR to attempt to solve this:

• Deprecate unnecessary escape characters #4176

[fabpot]

Can we close this one @ruudk?

[ruudk]

See #4176