Declaration emit for aliased exports used in export assignments is broken

[weswigham]

TypeScript Version: 2.7.0-dev.201xxxxx

Code

// @declaration: true
// @filename: /a.ts
class C {}
export { C as D }

// @filename: /b.ts
import * as a from "./a";
export default a.D;

Expected behavior:

// /a.d.ts
declare class C {}
export { C as D }
// /b.d.ts 
import * as a from "./a";
declare const _default: typeof a.D;
export default _default;

Actual behavior:

/b.ts(2,1): error TS4082: Default export of the module has or is using private name 'default'.


==== /a.ts (0 errors) ====
    class C {}
    export { C as D }
    
==== /b.ts (1 errors) ====
    import * as a from "./a";
    export default a.D;
    ~~~~~~~~~~~~~~~~~~~
!!! error TS4082: Default export of the module has or is using private name 'default'.

I think #19428 may have been an indicator of a larger issue, and the fix applied for it may have been too narrow (or it may be unrelated, haven't run a bisect yet). I've been having issues merging the fix into the symbol display builder PR (since it either fixes the observed bug and breaks all the type/symbol baselines or doesn't fix the bug, depending on how I merge it), so to track down how to implement the fix in the node builder instead of the symbol display builder I started looking for similar cases to see how we behave and found this.

[weswigham]

Root issue: a.D's type has a .symbol corresponding to the local symbol of C - which is reasonable. However the issue is in getAccessibleSymbolChain, which then returns the default export assignment of module b's symbol as the chain... which, perhaps obviously, has no visible declarations, as a default.