[ES|QL] separate command autocomplete routines

[drewdaemon]

The problem

The autocomplete logic for commands is currently designed to be generic. This is not a good fit for the ES|QL language since every command can have its own syntax and patterns. The generic approach currently leads to the following problems

• Lack of orthogonality—a change in the behavior in one area of the language often has side-effects in other parts of the language.
• Code complexity/understandability—the autocomplete routines are large, complicated, and difficult to follow. It is especially difficult to understand exactly which pieces of logic apply to which commands.

The plan

Instead of having getExpressionSuggestionsByType try to cover all commands, it should delegate to command-specific routines attached to the command definitions:

const commandDefinition = commandDefinitions
    .find(({name}) => ASTCommand.name == name);

return commandDefinition.suggest(...);

This should increase the orthogonality of the code, making it safer/easier to change behavior for some commands without affecting others.

By the end of this refactor, I expect the signature property in command definitions to be removed and the definitions to be paired down to very simple interfaces. We are moving away from declarative toward imperative, so the need for many of the command definition flags will be removed.

One drawback to this could be a lot of code duplication since there will still be overlap between commands. We can mitigate this by using a composable library of shared functions where syntax is close enough between commands.

{
    name: 'keep',
    ...
    suggest: (...) => {
        ...
        return handleFragment(
            innerText,
            (fragment) => Boolean(_getColumnByName(fragment)),
            getIncompleteSuggestions,
            getCompletedSuggestions
        );
    },
},
{
    name: 'drop',
    ...
    suggest: (...) => {
        ...
        return handleFragment(
            innerText,
            (fragment) => Boolean(_getColumnByName(fragment)),
            getIncompleteSuggestions,
            getCompletedSuggestions
        );
    },
},

Here, the handleFragment helper is used to handle field suggestions in two very similar commands: KEEP and DROP.

Hit list

• FROM
• ROW
• SHOW
• DISSECT
• DROP [ES|QL] separate KEEP, DROP, and SORT autocomplete routines #197744
• ENRICH
• EVAL
• GROK
• KEEP [ES|QL] separate KEEP, DROP, and SORT autocomplete routines #197744
• LIMIT
• MV_EXPAND
• RENAME
• SORT [ES|QL] separate KEEP, DROP, and SORT autocomplete routines #197744
• STATS ... BY [ES|QL] separate STATS autocomplete routine #198224
• WHERE [ES|QL] separate WHERE autocomplete routine #198832

[elasticmachine]

Pinging @elastic/kibana-esql (Team:ESQL)

[drewdaemon]

We should also monitor our bundle sizes during this refactor.