Parsing Shell Quotes Requires Parsing the Whole Language

This is example has four double quotes. To determine whether it means OPEN OPEN CLOSE CLOSE or OPEN CLOSE OPEN CLOSE requires a full shell parser.

$ echo "foo ${myvar:-"$(f() { echo func-defined-inside-quotes-and-inside-arg; }; f)"} bar"
foo func-defined-inside-quotes-and-inside-arg bar

$ myvar=x
$ echo "foo ${myvar:-"$(f() { echo func-defined-inside-quotes-and-inside-arg; }; f)"} bar"
foo x bar

3/2020 edit: Although I guess you do not have to parse f() { } in order to figure out that the first " is OPEN. You only have to understand that ${ is not closed yet, which is not that hard I suppose.

TODO: Come up with some harder cases.