completion returns no results with pattern matching.

[lbrayner]

These are the completion capabilities:

Completion capabilities

{
  "textDocument": {
    "completion": {
      "completionItem": {
        "commitCharactersSupport": true,
        "deprecatedSupport": true,
        "insertReplaceSupport": true,
        "insertTextModeSupport": {
          "valueSet": [
            1,
            2
          ]
        },
        "labelDetailsSupport": true,
        "preselectSupport": true,
        "snippetSupport": true,
        "tagSupport": {
          "valueSet": [
            1
          ]
        }
      },
      "completionList": {
        "itemDefaults": [
          "commitCharacters",
          "data",
          "editRange",
          "insertTextFormat",
          "insertTextMode"
        ]
      },
      "contextSupport": true,
      "dynamicRegistration": false,
      "insertTextMode": 1
    }
  }
}

Consider the following code:

import java.util.ArrayList;
import java.util.List;

public class SimpleJavaClass {
  public static void main(String[] args) {
    Object unknown = new ArrayList<>();

    if (unknown instanceof List things) {
      // things.is
      Object nothing = null;
      // things.is
    }
  }
}

textDocument/completion returns no results if requested for the first occurrence of things.is (uncommented, of course). It returns isEmpty(), however, for the second occurrence of thing.is.

Request for the first occurrence

{
  "method": "textDocument/completion",
  "params": {
    "position": {
      "character": 15,
      "line": 8
    },
    "textDocument": {
      "uri": "file:///var/tmp/jdtls-complete-fails/src/main/java/SimpleJavaClass.java"
    }
  }
}

Result for the first occurrence

{
  "isIncomplete": false,
  "itemDefaults": {
    "data": {
      "completionKinds": [ 9 ]
    }
  },
  "items": []
}

Request for the second occurrence

{
  "method": "textDocument/completion",
  "params": {
    "position": {
      "character": 15,
      "line": 10
    },
    "textDocument": {
      "uri": "file:///var/tmp/jdtls-complete-fails/src/main/java/SimpleJavaClass.java"
    }
  }
}

Result for the second occurrence

{
  "isIncomplete": false,
  "itemDefaults": {
    "data": {
      "completionKinds": [
        2,
        6
      ]
    },
    "editRange": {
      "insert": {
        "end": {
          "character": 15,
          "line": 10
        },
        "start": {
          "character": 13,
          "line": 10
        }
      },
      "replace": {
        "end": {
          "character": 15,
          "line": 10
        },
        "start": {
          "character": 13,
          "line": 10
        }
      }
    },
    "insertTextFormat": 2,
    "insertTextMode": 2
  },
  "items": [
    {
      "command": {
        "arguments": [
          "2",
          "0"
        ],
        "command": "java.completion.onDidSelect",
        "title": ""
      },
      "data": {
        "pid": "0",
        "rid": "2"
      },
      "detail": "List.isEmpty() : boolean",
      "filterText": "isEmpty() : boolean",
      "insertText": "isEmpty",
      "kind": 2,
      "label": "isEmpty",
      "labelDetails": {
        "description": "boolean",
        "detail": "()"
      },
      "sortText": "999999035",
      "textEditText": "isEmpty()"
    }
  ]
}

[rgrunber]

Definitely an upstream bug as well. It's interesting because it seemed to slightly work in earlier versions but regressed to the point of no support.