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Felipe Coury 98923e53cc
fix(tui): decode ANSI alpha-channel encoding in syntax themes (#13382)
## Problem

The `ansi`, `base16`, and `base16-256` syntax themes are designed to
emit ANSI palette colors so that highlighted code respects the user's
terminal color scheme. Syntect encodes this intent in the alpha channel
of its `Color` struct — a convention shared with `bat` — but
`convert_style` was ignoring it entirely, treating every foreground
color as raw RGB. This caused ANSI-family themes to produce hard-coded
RGB values (e.g. `Rgb(0x02, 0, 0)` instead of `Green`), defeating their
purpose and rendering them as near-invisible dark colors on most
terminals.

Reported in #12890.

## Mental model

Syntect themes use a compact encoding in their `Color` struct:

| `alpha` | Meaning of `r` | Mapped to |
|---------|----------------|-----------|
| `0x00` | ANSI palette index (0–255) | `RtColor::Black`…`Gray` for 0–7,
`Indexed(n)` for 8–255 |
| `0x01` | Unused (sentinel) | `None` — inherit terminal default fg/bg |
| `0xFF` | True RGB red channel | `RtColor::Rgb(r, g, b)` |
| other | Unexpected | `RtColor::Rgb(r, g, b)` (silent fallback) |

This encoding is a bat convention that three bundled themes rely on. The
new `convert_syntect_color` function decodes it; `ansi_palette_color`
maps indices 0–7 to ratatui's named ANSI variants.

| macOS - Dark | macOS - Light | Windows - ansi | Windows - base16 |
|---|---|---|---|
| <img width="1064" height="1205" alt="macos-dark"
src="https://github.com/user-attachments/assets/f03d92fb-b44b-4939-b2b9-503fde133811"
/> | <img width="1073" height="1227" alt="macos-light"
src="https://github.com/user-attachments/assets/2ecb2089-73b5-4676-bed8-e4e6794250b4"
/> |
![windows-ansi](https://github.com/user-attachments/assets/d41029e6-ffd3-454e-ab72-6751607e5d5c)
|
![windows-base16](https://github.com/user-attachments/assets/b48aafcc-0196-4977-8ee1-8f8eaddd1698)
|

## Non-goals

- Background color decoding — we intentionally skip backgrounds to
preserve the terminal's own background. The decoder supports it, but
`convert_style` does not apply it.
- Italic/underline changes — those remain suppressed as before.
- Custom `.tmTheme` support for ANSI encoding — only the bundled themes
use this convention.

## Tradeoffs

- The alpha-channel encoding is an undocumented bat/syntect convention,
not a formal spec. We match bat's behavior exactly, trading formality
for ecosystem compatibility.
- Indices 0–7 are mapped to ratatui's named variants (`Black`, `Red`, …,
`Gray`) rather than `Indexed(0)`…`Indexed(7)`. This lets terminals apply
bold/bright semantics to named colors, which is the expected behavior
for ANSI themes, but means the two representations are not perfectly
round-trippable.

## Architecture

All changes are in `codex-rs/tui/src/render/highlight.rs`, within the
style-conversion layer between syntect and ratatui:

```
syntect::highlighting::Color
  └─ convert_syntect_color(color)  [NEW — alpha-dispatch]
       ├─ a=0x00 → ansi_palette_color()  [NEW — index→named/indexed]
       ├─ a=0x01 → None (terminal default)
       ├─ a=0xFF → Rgb(r,g,b) (standard opaque path)
       └─ other  → Rgb(r,g,b) (silent fallback)
```

`convert_style` delegates foreground mapping to `convert_syntect_color`
instead of inlining the `Rgb(r,g,b)` conversion. The core highlighter is
refactored into `highlight_to_line_spans_with_theme` (accepts an
explicit theme reference) so tests can highlight against specific themes
without mutating process-global state.

### ANSI-family theme contract

The ANSI-family themes (`ansi`, `base16`, `base16-256`) rely on upstream
alpha-channel encoding from two_face/syntect. We intentionally do
**not** validate this contract at runtime — if the upstream format
changes, the `ansi_themes_use_only_ansi_palette_colors` test catches it
at build time, long before it reaches users. A runtime warning would be
unactionable noise.

### Warning copy cleanup

User-facing warning messages were rewritten for clarity:
- Removed internal jargon ("alpha-encoded ANSI color markers", "RGB
fallback semantics", "persisted override config")
- Dropped "syntax" prefix from "syntax theme" — users just think "theme"
- Downgraded developer-only diagnostics (duplicate override, resolve
fallback) from `warn` to `debug`

## Observability

- The `ansi_themes_use_only_ansi_palette_colors` test enforces the
ANSI-family contract at build time.
- The snapshot test provides a regression tripwire for palette color
output.
- User-facing warnings are limited to actionable issues: unknown theme
names and invalid custom `.tmTheme` files.

## Tests

- **Unit tests for each alpha branch:** `alpha=0x00` with low index
(named color), `alpha=0x00` with high index (`Indexed`), `alpha=0x01`
(terminal default), unexpected alpha (falls back to RGB), ANSI white →
Gray mapping.
- **Integration test:**
`ansi_family_themes_use_terminal_palette_colors_not_rgb` — highlights a
Rust snippet with each ANSI-family theme and asserts zero `Rgb`
foreground colors appear.
- **Snapshot test:** `ansi_family_foreground_palette_snapshot` — records
the exact set of unique foreground colors each ANSI-family theme
produces, guarding against regressions.
- **Warning validation tests:** verify user-facing warnings for missing
custom themes, invalid `.tmTheme` files, and bundled theme resolution.

## Test plan

- [ ] `cargo test -p codex-tui` passes all new and existing tests
- [ ] Select `ansi`, `base16`, or `base16-256` theme and verify code
blocks render with terminal palette colors (not near-black RGB)
- [ ] Select a standard RGB theme (e.g. `dracula`) and verify no
regression in color output
2026-03-04 12:03:34 -08:00
.codex/skills Add PR babysitting skill for this repo (#12513) 2026-02-22 15:36:28 -08:00
.devcontainer chore: install an extension for TOML syntax highlighting in the devcontainer (#1650) 2025-07-22 10:58:09 -07:00
.github Require deduplicator success before commenting (#13399) 2026-03-03 15:32:47 -07:00
.vscode chore: rm --all-features flag from rust-analyzer (#13381) 2026-03-03 11:44:54 -08:00
codex-cli Update pnpm versions to fix cve-2026-24842 (#12009) 2026-02-19 14:27:55 -08:00
codex-rs fix(tui): decode ANSI alpha-channel encoding in syntax themes (#13382) 2026-03-04 12:03:34 -08:00
docs Make js_repl image output controllable (#13331) 2026-03-03 16:25:59 -08:00
patches [bazel] Bump rules_rs and llvm (#13366) 2026-03-04 01:59:32 +00:00
scripts Add Windows direct install script (#12741) 2026-03-03 09:25:50 -08:00
sdk/typescript Update pnpm versions to fix cve-2026-24842 (#12009) 2026-02-19 14:27:55 -08:00
shell-tool-mcp refactor: delete exec-server and move execve wrapper into shell-escalation (#12632) 2026-02-23 20:10:22 -08:00
third_party Add feature-gated freeform js_repl core runtime (#10674) 2026-02-11 12:05:02 -08:00
.bazelignore [bazel] Improve runfiles handling (#10098) 2026-01-29 00:15:44 +00:00
.bazelrc [bazel] Bump rules_rs and llvm (#13366) 2026-03-04 01:59:32 +00:00
.bazelversion [bazel] Upgrade to bazel9 (#9576) 2026-01-21 13:25:36 +00:00
.codespellignore feat(network-proxy): structured policy signaling and attempt correlation to core (#11662) 2026-02-13 09:01:11 +00:00
.codespellrc feat(network-proxy): structured policy signaling and attempt correlation to core (#11662) 2026-02-13 09:01:11 +00:00
.gitignore gitignore bazel-* (#8911) 2026-01-08 07:50:58 -08:00
.markdownlint-cli2.yaml fix(tui): document paste-burst state machine (#9020) 2026-01-13 11:48:31 -08:00
.npmrc chore: migrate to pnpm for improved monorepo management (#287) 2025-04-18 16:25:15 -07:00
.prettierignore [apply-patch] Clean up apply-patch tool definitions (#2539) 2025-08-21 20:07:41 -07:00
.prettierrc.toml Initial commit 2025-04-16 12:56:08 -04:00
AGENTS.md feat: discourage the use of the --all-features flag (#12429) 2026-02-20 23:02:24 -08:00
announcement_tip.toml nit: test an (#10892) 2026-02-06 14:41:53 +01:00
BUILD.bazel [bazel] Bump rules_rs and llvm (#13366) 2026-03-04 01:59:32 +00:00
CHANGELOG.md Documentation improvement: add missing period (#3754) 2025-10-30 13:01:33 -07:00
cliff.toml docs(changelog): update install command to @openai/codex@<version> (#2073) 2025-10-18 11:02:22 -07:00
defs.bzl [bazel] Bump rules_rs and llvm (#13366) 2026-03-04 01:59:32 +00:00
flake.lock fix(nix): update flake for newer Rust toolchain requirements (#10302) 2026-01-31 11:34:53 -08:00
flake.nix fix(nix): use correct version from Cargo.toml in flake build (#11770) 2026-02-13 12:19:25 -08:00
justfile feat: discourage the use of the --all-features flag (#12429) 2026-02-20 23:02:24 -08:00
LICENSE Initial commit 2025-04-16 12:56:08 -04:00
MODULE.bazel [bazel] Bump rules_rs and llvm (#13366) 2026-03-04 01:59:32 +00:00
MODULE.bazel.lock [bazel] Bump rules_rs and llvm (#13366) 2026-03-04 01:59:32 +00:00
NOTICE Add feature-gated freeform js_repl core runtime (#10674) 2026-02-11 12:05:02 -08:00
package.json Update pnpm versions to fix cve-2026-24842 (#12009) 2026-02-19 14:27:55 -08:00
pnpm-lock.yaml chore: ensure pnpm-workspace.yaml is up-to-date (#10140) 2026-01-29 10:49:03 -08:00
pnpm-workspace.yaml chore: ensure pnpm-workspace.yaml is up-to-date (#10140) 2026-01-29 10:49:03 -08:00
rbe.bzl [bazel] Bump rules_rs and llvm (#13366) 2026-03-04 01:59:32 +00:00
README.md docs: mention Codex app in README intro (#11926) 2026-02-16 17:35:05 +01:00
SECURITY.md docs: add codex security policy (#12193) 2026-02-19 09:12:59 -08:00

npm i -g @openai/codex
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