variable support for interpreter

[ppisljar]

Summary

As already defined in the types, interpreter handlers can contain the list of variables. This PR adds the implementation needed for that to work:

• variables can be passed in as a configuration to expression executor or expression loader
• var function is added to the function registry, which has a single argument name and it would read that variable from the handlers.variables and return it.
• var_set (looking for better name suggestions) accepts a name and optionally a value and would update the variable with this value. If value is not provided context will be used as variable value. var_set function returns the same context it received (so it does not affect the following functions, unless they are using a variable that was updated)

when running the expression the app can decide if it wants local variables (dashboard would pass separate instance of variable object to each embeddable) or global variables shared among embeddables (same instance of variables object would be passed to all embeddables)

Closes #46908

Example

using variables provided by the app executing the expression:
esaggs indexPattern={var indexPattern} aggs={....} | ...

reusing context within another expression
esaggs .... | var_set storedContext | pie ....
var storedContext | table ...

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

• This was checked for cross-browser compatibility, including a check against IE11
• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[streamich]

Code LGTM, given the value falsy check, see below.

Also, would be nice to add unit tests for both functions.

[streamich]

In case value is falsy, like 0:

Suggested change

	if (!variables[args.name]) {
	if (variables[args.name] === undefined) {

or

Suggested change

	if (!variables[args.name]) {
	if (!variables.hasOwnProperty(args.name)) {

or maybe we could use a Map

Suggested change

	if (!variables[args.name]) {
	if (!variables.has(args.name)) {

[streamich]

Shall we throw here? Or maybe we could return undefined?

[ppisljar]

you are right, thanks!

[streamich]

(looking for better name suggestions)

For setting:

• def
• set
• var
• val
• let
• export
• define

For using:

• get
• use
• var
• val
• $

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 2e7e419

History

• 💚 Build #20542 succeeded 97677aa
• 💔 Build #20276 failed 216400225e6f72681ab67e8bf246d84df75a9611

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[bhavyarm]

@ppisljar how do we test this pr? Thanks!

[ppisljar]

this is currently not exposed in any way to the user, so its can't really be tested and should not have any implications for users.