monaco registerSignatureHelpProvider() causes error: Cannot read property 'signatures' of undefined

Question

I'm using Monaco 0.22.2 trying to bring up suggestions for function parameters. I've defined a simple example like so:

monaco.languages.registerSignatureHelpProvider('myCustomLang', {
    signatureHelpTriggerCharacters: ['(', ','],
    provideSignatureHelp: (model, position, token) => {
        return {
            activeParameter: 0,
            activeSignautre: 0,
                signatures: [{
                    label:'string of_string(string $string, int $start)',
                    parameters: [
                        {
                            label: 'string $string',
                            documentation: 'The input string'
                        },
                        {
                            label: 'int $start',
                            documentation: "if $start is non-negative...",
                        }
                    ]
                }]
        };
    }
});

However as soon as I type in "(" or "," to trigger this code, I get the error:

Cannot read property 'signatures' of undefined
TypeError: Cannot read property 'signatures' of undefined
    at ParameterHintsModel.eval (parameterHintsModel.js:166)
    at Generator.next (<anonymous>)
    at fulfilled (parameterHintsModel.js:19)
    at eval (errors.js:24)

What am I doing wrong? My regular simple suggestions show up, but I can't get potential function parameter suggestions to show up.

Answer 1

The response should be structured this way:

  monaco.languages.registerSignatureHelpProvider("myCustomLang", {
    signatureHelpTriggerCharacters: ["(", ","],
    provideSignatureHelp: (model, position, token) => {
      return {
        dispose: () => {},
        value: {
          activeParameter: 0,
          activeSignature: 0,
          signatures: [
            {
              label:
                "string substr(string $string, int $start [, int $length])",
              parameters: [
                {
                  label: "string $string",
                  documentation:
                    "The input string. Must be one character or longer.",
                },
                {
                  label: "int $start",
                  documentation:
                    "If $start is non-negative, the returned string will start at the $start'th position in string, counting from zero. For instance, in the string 'abcdef', the character at position 0 is 'a', the character at position 2 is 'c', and so forth.\r\nIf $start is negative, the returned string will start at the $start'th character from the end of string. If $string is less than $start characters long, FALSE will be returned.",
                },
                {
                  label: "int $length",
                  documentation:
                    "If $length is given and is positive, the string returned will contain at most $length characters beginning from $start (depending on the length of $string) If $length is given and is negative, then that many characters will be omitted from the end of $string (after the start position has been calculated when a start is negative). If $start denotes the position of this truncation or beyond, FALSE will be returned. If $length is given and is 0, FALSE or NULL, an empty string will be returned. If $length is omitted, the substring starting from $start until the end of the string will be returned.",
                },
              ],
            },
          ],
        },
      };
    },
  });

The response type is SignatureHelpResult, it should have a value and dispose method. The value should be SignatureHelp with activeParameter activeSignature and signatures