Advice on tests for matching and replacing code for `ast-grep`?

[dimitarvp]

Hello, Recently I've opened a PR in ast-grep: https://github.com/ast-grep/ast-grep/pull/749, that adds Elixir support to the tool so you can search and replace code from the command line. I've confirmed that it works for the several cases that I had in mind.

I can't open a discussion in this repo so I am opening an issue asking for advice on what kinds of matching and replacing would be good relevant tests for this tool? (It uses tree-sitter and tree-sitter-elixir.)

Example of a replace test I just added there is below. I am not asking you to be an expert in ast-grep's syntax, I am merely asking if you can give me ideas on less bare and more believable match / replace tests. I'll translate those to ast-grep rules.

Link to the Rust file exercising the Elixir tests: https://github.com/ast-grep/ast-grep/pull/749/files#diff-0ea893cc4bb08a539d62faa2f16dc54b322a191b18a5462f875f8731c47c6259

Input code:

Stream.map([1, 2, 3], fn x -> x * 2 end)

Search pattern:

Stream.map($$$ARGS)

Replacer:

Enum.map($$$ARGS)

Expected output:

Enum.map([1, 2, 3], fn x -> x * 2 end)

[jonatanklosko]

A few random ideas:

$LEFT = hd($RIGHT) -> [$LEFT | _] = $RIGHT

opts[$KEY] || $DEFAULT -> Keyword.get(opts, $KEY, $DEFAULT)

Mod.fun($ARG1, $ARG2) -> Mod.fun($ARG2, $ARG1)

Mod.fun($ARG1, $ARG2) -> Mod.fun($ARG1, option: $ARG2)

[dimitarvp]

Thank you! I just added those to the PR.

Maybe one more, with partial rewriting of a function's body from one idiom to another? 🤔

[dimitarvp]

Here's what I came up with (and the test works):

Input code:

for x <- ["budgie", "cat", "dog"], do: String.to_atom(x)

Search pattern:

for $I <- $LIST, do: $MODULE.$FUNCTION($I)

Replacer:

Enum.map($LIST, fn $I -> $MODULE.$FUNCTION($I) end)

Expected output:

Enum.map(["budgie", "cat", "dog"], fn x -> String.to_atom(x) end)

---

I think all that is quite sufficient.

@jonatanklosko Feel free to close this as completed anytime you wish. Thank you for the ideas, they were useful and have been coded.

[jonatanklosko]

Perhaps Mod.fun($DATA, fn $ARG -> $MOD.$FUN($ARG) end) -> Mod.fun($DATA, &$MOD.$FUN/1) :)

[dimitarvp]

Yeah, thought about it and even tried it, worked, but figured it's superfluous as it was very similar to the previous one.

And looking through the tests of the other languages, Elixir will have much better coverage than many. 😅