QuickInfo for ElementAccessExpression show original type when its type should be narrowed.

[ShuiRuTian]

TypeScript Version: 4.0 beta

Search Terms:

Code

type Tmp = { i1: string | null };

function f2(t: Tmp) {
    if (typeof t.i1 === "string") {
        const tmp = t.i1;
        tmp;  // string
        t.i1;//string
    }
}


function f21(t: Tmp) {
    if (typeof t.i1 === "string") {
        const tmp = t["i1"];
        tmp;  // string
        t["i1"]; // string|null
    }
}

function f22(t: Tmp) {
    if (typeof t["i1"] === "string") {
        const tmp = t.i1;
        tmp;  // string
        t.i1;//string
    }
}

function f12(t: Tmp) {
    if (typeof t["i1"] === "string") {
        const tmp = t["i1"];
        tmp;  // string
        t["i1"];// string|null
    }
}

Expected behavior:
The quickinfo for ElementAccessExpression should also be "string"

Actual behavior:
It shows not narrowed type.

Playground Link:
https://www.typescriptlang.org/play?#code/C4TwDgpgBAKgtmKBeKBvKBLAjALigZ2ACcMA7AcygB8pSBXAGwagF8BuAWAChuAzO0gGNgGAPakovAEwAKYHnhgAlGm5RMvKHPARRm4ADpsyJCgBEhEhTMrUa9VEPY2AeheWy5ey24+e--iERcUkpLDkFBFt7DE1tSD1HIywTcw9raK4HRwBtM2wzAF02KDcCYk8qeiZvX24+AWExCWlZeVgo1SyNLVAE-TyCwtSoCwqMruynLFd3ca9uvz8GoObJLDbI5Ume+N0B-KwikbGrchsd9WBBo+Ky9PIqxgZarhYgA

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