Remove the S-expression parsetree printer

[cknitt]

First step of #8798.

res_parser -print sexp printed the parsetree as an S-expression. Its only user was the formatter roundtrip test in scripts/test_syntax.sh, which formatted each file twice and checked two things:

• the two formatted texts are equal;
• the ASTs parsed from them, printed as S-expressions, are equal.

The parser is deterministic, so the second check holds whenever the first does. It never caught anything the text check didn't. The roundtrip test now only checks the text, and the printer goes. That's about 1,100 lines that every new parsetree node no longer has to handle.

The printer also printed the character offsets of explicit braces (braces_loc, since #8678) and no other locations. That was unintended and isn't carried over anywhere.

res_parser's other -print modes (ast, comments, doc, ml, res, tokens) are unchanged. res_parser isn't shipped in the npm packages, so this doesn't affect users.

🤖 Generated with Claude Code

https://claude.ai/code/session_013ZYFYMu3AE9P1xFVCR34d1

[cknitt]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-11T19:52:12.451952Z	42eea77	Manual request

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review" or "@codex security review".

Codex reacts with 👀 while any review is running, comments if it has suggestions, and reacts with 👍 once all reviews finish with no findings.

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 42eea77a81

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[pkg-pr-new]

Open in StackBlitz

rescript

npm i https://pkg.pr.new/rescript@8803

@rescript/belt

npm i https://pkg.pr.new/@rescript/belt@8803

@rescript/darwin-arm64

npm i https://pkg.pr.new/@rescript/darwin-arm64@8803

@rescript/darwin-x64

npm i https://pkg.pr.new/@rescript/darwin-x64@8803

@rescript/linux-arm64

npm i https://pkg.pr.new/@rescript/linux-arm64@8803

@rescript/linux-x64

npm i https://pkg.pr.new/@rescript/linux-x64@8803

@rescript/runtime

npm i https://pkg.pr.new/@rescript/runtime@8803

@rescript/win32-x64

npm i https://pkg.pr.new/@rescript/win32-x64@8803

commit: 42eea77

[github-actions]

Developer playground preview: https://rescript-lang.github.io/rescript/dev-playground/?version=pr-8803