Add template engine ADR

[InAnYan]

Mandatory checks

- [ ] Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
- [ ] Tests created for changes (if applicable)
- [ ] Manually tested changed features in running JabRef (always required)
- [ ] Screenshots added in PR description (for UI changes)
- [ ] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
- [ ] Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

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Refs koppor#392

[koppor]

Pleae add an example for each temlating engine. Just reading the pros and cons, one cannot really decide.

I think, the main decision driver is a "nice" syntax. - Please add this as first decision driver.

[github-actions]

You modified Markdown (*.md) files and did not meet JabRef's rules for consistently formatted Markdown files.
To ensure consistent styling, we have markdown-lint in place.
Markdown lint's rules help to keep our Markdown files consistent within this repository and consistent with the Markdown files outside here.

You can check the detailed error output by navigating to your pull request, selecting the tab "Checks", section "Tests" (on the left), subsection "Markdown".

[InAnYan]

I think you understand this is unfinished ADR, because I haven't used layout files and template engines much in Java.

I wrote everything for AI, and every option seems to be fine

[github-actions]

You modified Markdown (*.md) files and did not meet JabRef's rules for consistently formatted Markdown files.
To ensure consistent styling, we have markdown-lint in place.
Markdown lint's rules help to keep our Markdown files consistent within this repository and consistent with the Markdown files outside here.

You can check the detailed error output by navigating to your pull request, selecting the tab "Checks", section "Tests" (on the left), subsection "Markdown".

[koppor]

Fix linting issues

Add one example for each entry. Maye with an example of #11884.

                    #foreach( $entry in $entries )
                    ${CanonicalBibEntry.getCanonicalRepresentation($entry)}
                    #end""",

The example is good, because it shows

• forEach loops
• how to call existing functions

We should also add one function call for JabRef's functions - https://docs.jabref.org/collaborative-work/export/customexports

\format[HTMLChars,AuthorFirstFirst]{\editor}

New probably

$AuthorFirstFirst$(HTMLChars($entry.editor))

I am not sure about $entry.editor. Is it $entry.getField(editor).get()`? -- I don't want the template engine be verbose.

The current code is at org.jabref.logic.layout.LayoutEntry#handleOptionField. (Many class variables 🙈)

• Add new Decision Driver: Short and understandable syntax. Especially good handling of unset fields and empty Optionals.

[github-actions]

You modified Markdown (*.md) files and did not meet JabRef's rules for consistently formatted Markdown files.
To ensure consistent styling, we have markdown-lint in place.
Markdown lint's rules help to keep our Markdown files consistent within this repository and consistent with the Markdown files outside here.

You can check the detailed error output by navigating to your pull request, selecting the tab "Checks", section "Tests" (on the left), subsection "Markdown".

[koppor]

please all examples consistent

please remove all gempl te placeholders in the options

[koppor]

Why? 😅

[koppor]

• Please add the arguments of https://stackoverflow.com/a/1984458/873282 as pros/and cons. You can reference the answer as soruce: [[source](https://stackoverflow.com/a/1984458/873282)]

[koppor]

Reading the syntax, +1 for Velocity.

Velocity's goal is to keep templates as simple as possible

From: https://stackoverflow.com/a/1984458/873282

And this is what we mainly want!

[InAnYan]

I chose Apache Velocity

Sorry, on your all behalf :)

I want to complete this ADR

[koppor]

I think, text is good enough.