Add transformations for placeholders

[Christoph Seitz (go2sh)]

This PR adds transformations for placeholders by extending the syntax in the same way transformations are use with variables. Transformations are executed, when the user changes to the next placeholder.

I don't know if there is a better/more efficient way, but for me it works.

Fixes #34683.
TODO:

• Add tests
• Update documentation

PS: My first contribution to vscode. Great editor. :)
Best Regards,
go2sh

[Microsoft Contribution License Agreements (msftclas)]

All CLA requirements met.

[Christoph Seitz (go2sh)]

CC Johannes Rieken (@jrieken)

[Jose Menendez (menendezau)]

Nice work!

[Johannes Rieken (jrieken)]

👏 looks good so far, keep going esp. with adding tests. Check out snippetParser.test.ts and snippetSession.test.ts. Left a few questions about the grammar/rule-of-transform as comments

[Johannes Rieken (jrieken)]

Not sure if that's actually supported by TextMate. Do you have a reference?

[Christoph Seitz (go2sh)]

As far as I know, TextMate only supports transformations for the simple case ${1/.../.../...}. This two here would be an extension to the TextMate behavior. I agree, that the choice case might not be needed, but the nested one would be nice for default values, which covers exactly my use case. I implemented transformations for all case to have a consistent behavior.

[Christoph Seitz (go2sh)]

For Reference: http://manual.macromates.com/en/snippets#transformations

[Christoph Seitz (go2sh)]

Another thing that differs from the TextMate behavior is that only the first placeholder is used for the transformation. I'll change that as well, so that every placeholder can holde it's own transformation.

[Christoph Seitz (go2sh)]

Johannes Rieken (@jrieken) I fixed the code and added quite some tests. I hope this is enough for merging. ;-)

Now VS Code supports:

${1/.../.../...}
${1:.../.../.../...}
${1|...|/.../.../...}

Which is a super set of the TextMate Syntax. So tm snippets work in vscode, but extended vscode snippets don't work in tm. Every placeholder has its one transformation, so you can create two different results for the same index.

[Johannes Rieken (jrieken)]

Thanks - quite busy the next few days but my hope is to squeeze this in during this week...

[Christoph Seitz (go2sh)]

Would be nice to see it in the next Update. I use this feature a lot. :-)

[Johannes Rieken (jrieken)]

Bang on. Thanks! Two small things left:

• please add a test in snippetSession.test that uses two (or more) selection at different indentation. Like test('snippets, transform'... but with multiple selection. I test this manually but it would be best to have tested too.
• update snippet.md with a placeholder transform section and please outline what isn't standard TM.

Scheduled this now for June, let's ship this.

[Christoph Seitz (go2sh)]

Johannes Rieken (@jrieken) Done. :)

[Johannes Rieken (jrieken)]

Thanks.

[Johannes Rieken (jrieken)]

Merged! 🍻 Christoph Seitz (@go2sh)

[Beau Smith (beausmith)]

How to use /upcase, /downcase/, and /capitalize?

I've read the docs and tried:

"test": {
    "prefix": "test",
    "body": "${1} -> ${1:/upcase} ${1:/downcase}"
},

and

"test": {
    "prefix": "test",
    "body": "${1} -> ${1/upcase} ${1/downcase}"
},

…but neither work.

I don't see any tests for these transforms in this PR.

I'm stumped. I posted a question here:
https://stackoverflow.com/questions/51272365/vs-code-how-to-convert-snippet-placeholder-to-uppercase-or-lowercase

cc Christoph Seitz (@go2sh)

[Martien Oranje (moranje)]

The integer in the EBNF docs refers to a RegExp group not to a tabstop reference so should work when typing Asdf:

    "test": {
        "prefix": "test",
        "body": "${1} -> ${1/(Asdf)/${1:/upcase}/} ${1/(Asdf)/${1:/downcase}/}"
    }

[Christian Rapelius-Saar (csaar95)]

In addition to #34683, it also doesn't support choice: "${1|hello,world|} -> ${1/hello/hallo/}"

[Georgii Dolzhykov (thorn0)]

Can't make ${1:.../.../.../...} work in 1.27.0-insiders.

[Christoph Seitz (go2sh)]

Beau Smith (@beausmith) Martien Oranje (@moranje) Christian Rapelius-Saar (@csaar95) Georgii Dolzhykov (@thorn0) The vscode team removed all the advanced options as they create some regressions on existing snippets. See the docs. Only ${1/../../} is supported. Sorry for that. The removal also broke my usecase...

[Georgii Dolzhykov (thorn0)]

The docs aren't clear about this. The Grammar section doesn't include placeholder transforms at all. At the same time, the Placeholder Transform section doesn't have any examples and doesn't mention whether transforms can be combined with default values. So it's not really clear what supposed to be supported and what is not.

[Christoph Seitz (go2sh)]

The grammar is clear. Transform is only valid for a tab-stop or a variable. The docs are not perfect. I try to make a pr. The Placeholder Transform section is from a time, where every thing was possible.

[Georgii Dolzhykov (thorn0)]

Ah, now I see it.

[Timothy (tecosaur)]

I'm trying a simple "$1 ${1/(.*)/${1:/upcase}/}" snippet but it isn't working for me (v1.40.0), has placeholder transform functionality just been completely removed?

[Antoni Mur (mib32)]

I'm trying a simple "$1 ${1/(.*)/${1:/upcase}/}" snippet but it isn't working for me (v1.40.0), has placeholder transform functionality just been completely removed?

Was struggling with this for a while, then understood - the transformation is not applied in real time - you have to hit Tab, and then it will get applied. Funny!