Tslint: Unnecessary `no-unused-expression`

[aghArdeshir]

Bug Report

• __TSLint version__: 5.11.0
• __TypeScript version__: 3.1.1
• __Running TSLint via__: VSCode

TypeScript code being linted

const buyers = this.propertiesChartDOM.nativeElement.getContext('2d');
    new Chart(buyers, {
      type: 'line',
      data: buyerData
    });

with tslint.json configuration:

{
    "extends": "../tslint.json",
    "rules": {
        "directive-selector": [
            true,
            "attribute",
            "phx",
            "camelCase"
        ],
        "component-selector": [
            true,
            "element",
            "phx",
            "kebab-case"
        ]
    }
}

{
  "rulesDirectory": [
    "node_modules/codelyzer"
  ],
  "rules": {
    "arrow-return-shorthand": true,
    "callable-types": true,
    "class-name": true,
    "comment-format": [
      true,
      "check-space"
    ],
    "curly": true,
    "deprecation": {
      "severity": "warn"
    },
    "eofline": true,
    "forin": true,
    "import-blacklist": [
      true,
      "rxjs/Rx"
    ],
    "import-spacing": true,
    "indent": [
      true,
      "spaces"
    ],
    "interface-over-type-literal": true,
    "label-position": true,
    "max-line-length": [
      true,
      140
    ],
    "member-access": false,
    "member-ordering": [
      true,
      {
        "order": [
          "static-field",
          "instance-field",
          "static-method",
          "instance-method"
        ]
      }
    ],
    "no-arg": true,
    "no-bitwise": true,
    "no-console": [
      true,
      "debug",
      "info",
      "time",
      "timeEnd",
      "trace"
    ],
    "no-construct": true,
    "no-debugger": true,
    "no-duplicate-super": true,
    "no-empty": false,
    "no-empty-interface": true,
    "no-eval": true,
    "no-inferrable-types": [
      true,
      "ignore-params"
    ],
    "no-misused-new": true,
    "no-non-null-assertion": true,
    "no-redundant-jsdoc": true,
    "no-shadowed-variable": true,
    "no-string-literal": false,
    "no-string-throw": true,
    "no-switch-case-fall-through": true,
    "no-trailing-whitespace": true,
    "no-unnecessary-initializer": true,
    "no-unused-expression": true,
    "no-use-before-declare": true,
    "no-var-keyword": true,
    "object-literal-sort-keys": false,
    "one-line": [
      true,
      "check-open-brace",
      "check-catch",
      "check-else",
      "check-whitespace"
    ],
    "prefer-const": true,
    "quotemark": [
      true,
      "single"
    ],
    "radix": true,
    "semicolon": [
      true,
      "always"
    ],
    "triple-equals": [
      true,
      "allow-null-check"
    ],
    "typedef-whitespace": [
      true,
      {
        "call-signature": "nospace",
        "index-signature": "nospace",
        "parameter": "nospace",
        "property-declaration": "nospace",
        "variable-declaration": "nospace"
      }
    ],
    "unified-signatures": true,
    "variable-name": false,
    "whitespace": [
      true,
      "check-branch",
      "check-decl",
      "check-operator",
      "check-separator",
      "check-type"
    ],
    "no-output-on-prefix": true,
    "use-input-property-decorator": true,
    "use-output-property-decorator": true,
    "use-host-property-decorator": true,
    "no-input-rename": true,
    "no-output-rename": true,
    "use-life-cycle-interface": true,
    "use-pipe-transform-interface": true,
    "component-class-suffix": true,
    "directive-class-suffix": true
  }
}

(my angular-cli project produces two tslint.jsons, I pasted them both)

Actual behavior

new Chart(buyers, {...}); initiates a chart on the first input to the function, which is a canvas 2D context; and then no more operations are needed.

Expected behavior

Well! That is not unused! It does something, and does it well! Finish :)

P.S.
I'm not sure if this is an issue related to tslint, or some other package, or I'm using it wrong! So I started an issue here.

[JoshuaKGoldberg]

@Ardeshir81 thanks for posting this! This is the right place to post your issue.

You're in luck: the rule has an allow-new option to allow this kind of usage. See https://palantir.github.io/tslint/rules/no-unused-expression/