[Lldb-commits] [lldb] [lldb][Format] Make function name frame-format variables work without debug-info (PR #137408)

[Pavel Labath via lldb-commits]

labath wrote:

> > As for the syntax for alternatives, I was suggesting (privately, I think) to use :-, as that what [bash](https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html) uses for conditional expansion (and the formatter language feels more like bash than C). However, I am having some doubts about that now since the way you're thinking of using it is not exactly bash-like (the :- thingy only works for a single variable, but I think you want to mostly use it on the block level (and bash doesn't have blocks))
> 
> Would the syntax be `${some.variable :- fallback.variable}`? Which would try the first and if that fails try the fallback? This would work for my use-case. I.e., `${function.formatted-arguments :- function.arguments}`

So, the bash syntax requires another level of `${}` if you want to treat the RHS as a variable (I guess, because something like `echo "FOO is ${FOO:-unset}"` is a common pattern). It also requires there be no spaces around the `:-` thingy.


```
$ FOO=bar
$ echo ${NOTSET:-FOO}
FOO
$ echo ${NOTSET:-${FOO}}
bar
$ echo ${NOTSET :- ${FOO}}
bash: ${NOTSET :- ${FOO}}: bad substitution
```

If it were to be used only on a single variable, then I think this syntax is great (including the nested expansion, since you also might want to replace the expansion with a constant string). For blocks (which I think makes sense), I'm less sure.

There's also a question of how to parse that (i.e., how to print a literal `:-`). With a single variable that's not an issue since variable names can't contain `:`). Though that's kind of a question regardless of the string...

https://github.com/llvm/llvm-project/pull/137408