If exported variable is renamed, tsc will generate code with a syntax error

[gdh1995]

TypeScript Version: typescript@4.0.0-dev.20200611 (also 3.9.5)

Search Terms: exported variable renamed

Code

// a.ts
let foo = 1
export { foo as fooValue }
export const testFoo = (val: number) => {
  if (val <= ++foo) {
    return val
  }
  return foo
}

And then run this in a terminal:

npx tsc a.ts && cat a.js

Expected behavior:

The command should output:

"use strict";
exports.__esModule = true;
exports.testFoo = exports.fooValue = void 0;
var foo = 1;
exports.fooValue = foo;
exports.testFoo = function (val) {
    if (val <= (exports.fooValue = ++foo)) {
        return val;
    }
    return foo;
};

Actual behavior:

The actual output is as the below, and require('./a.js') in Node.JS throws a SyntaxError

"use strict";
exports.__esModule = true;
exports.testFoo = exports.fooValue = void 0;
var foo = 1;
exports.fooValue = foo;
exports.testFoo = function (val) {
    if (val <= exports.fooValue = ++foo) {
        return val;
    }
    return foo;
};

If I run require("./a.js") in node, then it outputs:

Thrown:
R:\working\2\a.js:7
    if (val <= exports.fooValue = ++foo) {
        ^^^^^^^^^^^^^^^^^^^^^^^

SyntaxError: Invalid left-hand side in assignment

Playground Link: https://www.staging-typescript.org/play?target=1&module=1#

Related Issues: None

[gdh1995]

Um, I found another related bug: val <= foo-- will be transformed into val <= exports.fooValue = foo -= 1 - both a SyntaxError and a logic mistake, because the old value of foo is aborted.

[gdh1995]

@a-tarasyuk Hello, there's still a related case which seems not fixed:

Um, I found another related bug: val <= foo-- will be transformed into val <= exports.fooValue = foo -= 1 - both a SyntaxError and a logic mistake, because the old value of foo is aborted.

In the test files of your PR, it looks like that y <= x-- will be transformed into y <= (exports.x = x -= 1) ...

@rbuckton Should I open a new issue for it?