Support undercurl SGR styling

[jbetala7]

Fixes #5633.

Summary

• Parse SGR underline style subparameters for single, double, and curly underline, plus underline color (58) and reset (59).
• Store underline color in terminal cells and flat scrollback style data.
• Render curly underline decorations and use the SGR underline color when present.
• Preserve undercurl/underline color in grid string serialization and underline ref-test data.

Verification

• cargo check -p warp --lib
• cargo test -p warp_terminal test_contains_cell_decorations
• cargo test -p warp_terminal test_push_rows_with_color

Visual proof

• Final screen recording: https://raw.githubusercontent.com/jbetala7/warp/proof-10560-undercurl-final/warp-undercurl-screen-recording.mov
• Captured from the locally built PR branch (./target/debug/warp-oss, commit 38e2f1a3) in WarpOss. The video shows normal terminal output and alternate-screen output with curly underline plus explicit underline color.

Notes

• Attempted cargo test -p warp test_parsing_undercurl_and_underline_color, but the local machine ran out of disk while compiling unrelated app test dependencies (lsp, ai, tantivy, warp_graphql) before the test could run.

[cla-bot]

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[oz-for-oss]

@jbetala7

I'm starting a first review of this pull request.

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[jbetala7]

@cla-bot check

[cla-bot]

The cla-bot has been summoned, and re-checked this pull request!

[oz-for-oss]

Overview

This PR adds parsing, storage, rendering, and serialization support for SGR curly underline and underline colors.

Concerns

• Curly underline positioning appears incorrect: the new y value is later offset by the decoration height again, which moves the wave too far above the cell bottom.
• This is a user-visible terminal styling change, but the PR context does not include screenshots, a screen recording, or a successful app-level verification of the undercurl rendering. Manual testing is required for changes that can be manually tested. Please include screenshots or a screen recording that show it working end to end, or justify why manual testing is not possible.

Verdict

Found: 0 critical, 2 important, 0 suggestions

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[oz-for-oss]

⚠️ [IMPORTANT] This y value is subtracted by the decoration height again when building origin, so curly underlines render too far above the cell bottom. Use the cell bottom as the baseline for this decoration.

Suggested change

	thickness * 3.,
	cell_size.y() - thickness * 3.,
	thickness * 3.,
	cell_size.y(),

[jbetala7]

Addressed the requested undercurl positioning change in 38e2f1a3 by using cell_size.y() as the curly underline baseline, so the shared decoration origin applies the decoration-height offset once.

Verification run on the current head:

• cargo fmt --check
• git diff --check
• cargo check -p warp --lib

I do not have a reliable app-level visual screenshot from this local environment. The broader app-level verification was previously blocked locally by resource/environment constraints while compiling unrelated app test dependencies, so I am noting that limitation here rather than attaching a misleading screenshot. The renderer-level positioning concern has been corrected in code and the current head now passes the checks above.

/oz-review

[oz-for-oss]

@jbetala7

I'm re-reviewing this pull request in response to a review request.

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I reviewed this pull request and requested human review from: @warpdotdev/oss-maintainers.

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Oz no longer requests changes for this pull request after the latest automated review.

[oz-for-oss]

Overview

This PR adds SGR parsing, cell/scrollback storage, serialization, and rendering support for curly underline and underline color.

Concerns

• No blocking correctness or security concerns found in the annotated diff.

Verdict

Found: 0 critical, 0 important, 0 suggestions

Approve

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[lucieleblanc]

Hi @jbetala7, thanks for taking on this issue. This is a big user-facing change so it needs a screen capture. Please attach a screen recording to the PR description in which the curly underline and underline color are shown working correctly, both in standard terminal blocks and in alt screen programs (full-pane terminal interfaces, like Neovim or another text editor with LSP). On MacOS, you can start a screen recording using cmd-shift-5.

Please remove the linter steps from the PR description. They are presubmit checks, not proof of correctness.

Feel free to comment or re-request review when ready and we'll take another look!

[lucieleblanc]

Why did these serde annotations change? This is the kind of change that would be great to explain with an inline GitHub comment.

[jbetala7]

They changed so CellExtra stays sparse now that the struct has three independent optional fields. underline_color can exist without zero-width text or an end-of-prompt marker, and existing CellExtra values can exist without an underline color. Without skip_serializing_if, those cases would serialize unrelated null keys and churn the stored/ref-test JSON; without default, omitted optional keys in older or sparse serialized payloads would not be handled explicitly. No behavior change was intended for the existing fields.

[jbetala7]

Uploaded a cleaner final screen recording from the locally built PR branch (./target/debug/warp-oss, commit 38e2f1a3):

https://raw.githubusercontent.com/jbetala7/warp/proof-10560-undercurl-final/warp-undercurl-screen-recording.mov

I sampled the capture before posting it. It shows regular terminal output with curly underline plus underline color, then a full-screen/alternate-screen sequence using DEC 1049h/1049l with colored curly underline and underline color.

[lucieleblanc]

I sampled the capture before posting it

The point of the screen capture is to show an end-to-end flow (seeing the cursor, typing, etc.). but there is no difference between this "sampled" clip and a series of static screenshots. I would encourage you to run this manually and record the full interaction 🙂 it's fine to have an LLM generate a helper script or other material that you use for the demo, but ultimately the screen recording should show a human using the feature, with typing/clicking, opening and closing programs, etc.

I'll be happy to review this again with an actual recording! Otherwise this will be on the back burner.