Duplicate identifier error in services for commonjs `module.exports.prop = `

TypeScript Version: 2.9.0-dev.20180510

Code

a.js

module.exports = class C {};
module.exports.D = class D {};

b.js

const a = require("./a");

Open the two tabs side-by-side in an editor. Initially there is no error, but when you make any edit (e.g., adding a newline) to b.js, then module.exports.D in a.js is marked with an error Duplicate identifier 'D'. (Making any edit to a.js will make it go away, but then editing b.js makes it come back...)

CC @sandersn

[sandersn]

Note that adding a third line in a.js, var d = new D(), causes a crash in resolveName, even from the command line. I'll file that as a separate bug.

[sandersn]

@Andy-MS helped me find a repro that works from the command line. Put the require in the same file:

var wat = require('./test')
module.exports = class C {}
module.exports.D = class D { }

Note that the require has to be first. My current hypothesis is that getCommonJsExportEquals creates a merged symbol which is !== the symbol for class D, thereby evading the check I added in #24466. I have a simpler fix that I will put up shortly.