`typescript.SymbolTable` does not properly implement the ES6 Map interface

[Zemnmez]

TypeScript Version: 3.7.3

The typescript.SymbolTable is like an ES6 Map -- typescript.d.ts describes it as 'based on the ES6 Map interface'.

However, the underlying interface typescript.UnderscoreEscapedMap does not implement the Map interface, or the Iterable, or Iterator protocols. This means it's not possible to iterate over properly without shim code, which varies from manually implementing the Iterator protocol (annoying!) to overriding the type with as Map<ts.__String, ts.Symbol> (bad!).

Code Example

import * as ts from "typescript";

const p = ts.createProgram(["t.d.ts"], {});
const c = p.getTypeChecker();
p.getSourceFiles().map(f => {
    f.forEachChild(n => {
        if (!ts.isModuleDeclaration(n)) return;
        const s = c.getSymbolAtLocation(n.name);
        if (!s) return;

        const scanMembers = (s: ts.Symbol) => {
            if (s.valueDeclaration === undefined)
                console.log("missing valueDeclaration on", s.getName());

            type m = Iterator<any>
            if (!s.exports) return;
            if (!(Symbol.iterator in s.exports))
                return console.log("not iterable", s.getName())
            for (let [/*name*/, member] of (s.exports as Map<ts.__String, ts.Symbol>)) {
                scanMembers(member);
            }
        }

        scanMembers(s);


    })
})

typescript.UnderscoreEscapedMap is not recognized as a Map due to clear(), delete(), set(), [Symbol.toStringTag] and [Symbol.iterator] being undefined.

Testing map assertion

// Type 'ReadonlyUnderscoreEscapedMap<any>' is missing the following properties
// from type 'Map<any, any>': clear, delete, set, [Symbol.iterator],
// [Symbol.toStringTag] ts(2739)
const x: Map<any, any> = void 0 as any as ts.ReadonlyUnderscoreEscapedMap<any>

Perhaps this is a compiler internals issue, as using as Map<ts.__String, ts.Symbol> makes SymbolTables work without issue. If it's not, the fix should be as simple as replacing typescript.UnderscoreEscapedMap with Map and typescript.ReadonlyUnderscoreEscapedMap with ReadonlyMap.

Search Terms:

Code

import * as ts from "typescript";

const p = ts.createProgram(["t.d.ts"], {});
const c = p.getTypeChecker();
p.getSourceFiles().map(f => {
    f.forEachChild(n => {
        if (!ts.isModuleDeclaration(n)) return;
        const s = c.getSymbolAtLocation(n.name);
        if (!s) return;

        const scanMembers = (s: ts.Symbol) => {
            if (s.valueDeclaration === undefined)
                console.log("missing valueDeclaration on", s.getName());

            type m = Iterator<any>
            if (!s.exports) return;
            if (!(Symbol.iterator in s.exports))
                return console.log("not iterable", s.getName())

            // error!!
            for (let [/*name*/, member] of s.exports) {
                scanMembers(member);
            }
        }

        scanMembers(s);


    })
})

Expected behavior:
It should be possible to iterate over a typescript.SymbolTable.

Actual behavior:
typescript.SymbolTable is considered not iterable.

[Gerrit0]

Perhaps this is a compiler internals issue, as using as Map<ts.__String, ts.Symbol> makes SymbolTables work without issue.

Everywhere except old IE, which will use src/shims/mapShim.ts.

I'd like love for the shim to go away and to switch to the standard map definition, this gets in my way frequently.

[tamj0rd2]

Is this on any roadmap? Not being able to iterate through symbol tables in a standard way makes life a bit difficult

[JaKXz]

Hi, sorry to comment on an old issue but I share the sentiment here 😅 I'm curious, does the UnderscoreEscapedMap preclude the SymbolTable from being iterable? Or am I reading that wrong and this is just on the backburner?

Or, would it be possible to have a method similar to getExportsOfModule to return an Array?

[jakebailey]

Old old issue but SymbolTable has been Map since #51439