Bug: catch var dropped as unused

[pvdz]

• Bug report or feature request?
  Bug. Found by fuzzer.

• uglify-js version (uglifyjs -V)
  Git master, f71f490

I think this means #1708 isn't completely solved yet.

var a = 100, b = 10, c = 0;
function f() {
    try {
    } catch (b) {
        return;
        try {
        } catch (foo) {
            var b = 999;
        }
    } finally {
        --b
    }
}
f();
console.log(null, a, b, c);

$ bin/uglifyjs s.js -c && bin/uglifyjs s.js -c passes=3 && bin/uglifyjs s.js -c passes=3 -m 
WARN: Dropping unreachable code [s.js:6,8]
WARN: Declarations in unreachable code! [s.js:8,12]
function f(){try{}catch(b){return}finally{--b}}var a=100,b=10,c=0;f(),console.log(null,a,b,c);
WARN: Dropping unreachable code [s.js:6,8]
WARN: Declarations in unreachable code! [s.js:8,12]
function f(){try{}catch(b){return}finally{--b}}var a=100,b=10,c=0;f(),console.log(null,a,b,c);
WARN: Dropping unreachable code [s.js:6,8]
WARN: Declarations in unreachable code! [s.js:8,12]
function f(){try{}catch(b){return}finally{--b}}var a=100,b=10,c=0;f(),console.log(null,a,b,c);

$ cat s.js | node && node s.js && bin/uglifyjs s.js -c | node && bin/uglifyjs s.js -c passes=3 | node && bin/uglifyjs s.js -c passes=3 -m | node
null 100 10 0
null 100 10 0
WARN: Dropping unreachable code [s.js:6,8]
WARN: Declarations in unreachable code! [s.js:8,12]
null 100 9 0
WARN: Dropping unreachable code [s.js:6,8]
WARN: Declarations in unreachable code! [s.js:8,12]
null 100 9 0
WARN: Dropping unreachable code [s.js:6,8]
WARN: Declarations in unreachable code! [s.js:8,12]
null 100 9 0

[alexlamsl]

This one is due to drop_unused failing to extract declarations - fixing... 🤖

[alexlamsl]

Minimal test case:

options = {
    unused: true,
}
input: {
    var a = 1;
    function f() {
        a++;
        try {} catch (a) {
            var a;
        }
    }
    f();
    console.log(a);
}