Render uses of deprecated symbols

[mjbvz]

TypeScript Version: 3.6.0-rc

Search Terms:

• diagnostics
• errors
• suggestions
• suggestion diagnostics
• deprecated

Feature request
VS Code recently added special for special rendering of error spans for deprecated symbols: microsoft/vscode#56694 These are rendered as strike out in the editor

We would like the TypeScript server to also generate suggestion diagnostics for uses of deprecated symbols:

/**
 * @deprecated
 */
function foo() {}

foo() /* Call to `foo` should rendered with a strike out*/

Proposed API change
This feature is broadly similar to how TypeScript supports rendering unused diagnostics. Unused diagnostics are indicated by a reportsUnnecessary field on the diagnostic.

To support deprecated diagnostics as well, we could add a new reportsDeprecated field

[Trace  - 2:56:06 PM] <semantic> Event received: suggestionDiag (0).
Data: {
    "file": "/Users/matb/projects/san/index.ts",
    "diagnostics": [
        {
            "start": {
                "line": 6,
                "offset": 10
            },
            "end": {
                "line": 6,
                "offset": 13
            },
            "text": "'foo' is marked deprecated.",
            "code": 6133,
            "category": "suggestion",
            "reportsDeprecated": true
        }
    ]
}

VS Code would provide the support for enabling/disabling deprecated diagnostics; TS Server just needs to return this information to us

Related Issues:

• Add flag to mark TS Server unused variable suggestion diagnostics #23288