[ES|QL] Fix autocomplete for incomplete show command (elastic#175292)

## Summary

Fix a regression on `SHOW` command autocomplete within 8.13 (so no
public bug).
Compared to the previous custom grammar, the ES one does support the
`SHOW` command only in complete mode (`SHOW FUNCTIONS` or `SHOW INFO`):
any other substring (i.e. `SHOW`) will trigger an error at grammar level
and will not be handled by the AST provider (as it won't enter the
ParserTree at all).

This time I've added unit tests for the autocomplete to avoid
regressions like this again.


![show_functions_fix](https://github.com/elastic/kibana/assets/924948/a9eea572-91ea-43d2-bd2e-ede61996866e)

### Checklist

- [x] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

---------

Co-authored-by: Stratoula Kalafateli <[email protected]>

packages/kbn-monaco/src/esql/lib/ast/autocomplete/autocomplete.test.ts

@@ -317,6 +317,13 @@ describe('autocomplete', () => {
     testSuggestions('from index', suggestedIndexes, 6 /* index index in from */);
   });
 
+  describe('show', () => {
+    testSuggestions('show ', ['functions', 'info']);
+    for (const fn of ['functions', 'info']) {
+      testSuggestions(`show ${fn} `, ['|']);
+    }
+  });
+
   describe('where', () => {
     const allEvalFns = getFunctionSignaturesByReturnType('where', 'any', {
       evalMath: true,

packages/kbn-monaco/src/esql/lib/ast/autocomplete/autocomplete.ts

@@ -603,6 +603,11 @@ async function getExpressionSuggestionsByType(
             }
           ))
         );
+        if (command.name === 'show') {
+          suggestions.push(
+            ...getBuiltinCompatibleFunctionDefinition(command.name, undefined, 'any')
+          );
+        }
       }
     }
 

packages/kbn-monaco/src/esql/lib/ast/autocomplete/complete_items.ts

@@ -41,9 +41,10 @@ export const getBuiltinCompatibleFunctionDefinition = (
       !ignoreAsSuggestion &&
       !/not_/.test(name) &&
       (option ? supportedOptions?.includes(option) : supportedCommands.includes(command)) &&
-      signatures.some(({ params }) => params.some((pArg) => pArg.type === argType))
+      signatures.some(
+        ({ params }) => !params.length || params.some((pArg) => pArg.type === argType)
+      )
   );
-
   if (!returnTypes) {
     return compatibleFunctions.map(getAutocompleteBuiltinDefinition);
   }

packages/kbn-monaco/src/esql/lib/ast/autocomplete/factories.ts

@@ -51,10 +51,11 @@ export function getAutocompleteFunctionDefinition(fn: FunctionDefinition) {
 }
 
 export function getAutocompleteBuiltinDefinition(fn: FunctionDefinition) {
+  const hasArgs = fn.signatures.some(({ params }) => params.length);
   return {
     label: fn.name,
-    insertText: `${fn.name} $0`,
-    insertTextRules: 4, // monaco.languages.CompletionItemInsertTextRule.InsertAsSnippet,
+    insertText: hasArgs ? `${fn.name} $0` : fn.name,
+    ...(hasArgs ? { insertTextRules: 4 } : {}), // monaco.languages.CompletionItemInsertTextRule.InsertAsSnippet,
     kind: 11,
     detail: fn.description,
     documentation: {

packages/kbn-monaco/src/esql/lib/ast/shared/context.ts

@@ -157,6 +157,23 @@ export function getAstContext(innerText: string, ast: ESQLAst, offset: number) {
       return { type: 'setting' as const, command, node, option, setting };
     }
   }
+  if (!command && innerText.trim().toLowerCase() === 'show') {
+    return {
+      type: 'expression' as const,
+      // The ES grammar makes the "SHOW" command an invalid type at grammar level
+      // so we need to create a fake command to make it work the AST in this case
+      command: {
+        type: 'command',
+        name: 'show',
+        text: innerText.trim(),
+        location: { min: 0, max: innerText.length },
+        incomplete: true,
+        args: [],
+      } as ESQLCommand,
+      node,
+      option,
+    };
+  }
 
   if (!command || (innerText.length <= offset && getLastCharFromTrimmed(innerText) === '|')) {
     //   // ... | <here>

packages/kbn-monaco/src/esql/lib/ast/validation/validation.test.ts

@@ -488,6 +488,10 @@ describe('validation logic', () => {
     testErrorsAndWarnings('show', ['SyntaxError: expected {SHOW} but found "<EOF>"']);
     testErrorsAndWarnings('show functions', []);
     testErrorsAndWarnings('show info', []);
+    testErrorsAndWarnings('show functions()', [
+      "SyntaxError: token recognition error at: '('",
+      "SyntaxError: token recognition error at: ')'",
+    ]);
     testErrorsAndWarnings('show functions blah', [
       "SyntaxError: token recognition error at: 'b'",
       "SyntaxError: token recognition error at: 'l'",