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feat(tui): syntax highlighting via syntect with theme picker (#11447)
## Summary Adds syntax highlighting to the TUI for fenced code blocks in markdown responses and file diffs, plus a `/theme` command with live preview and persistent theme selection. Uses syntect (~250 grammars, 32 bundled themes, ~1 MB binary cost) — the same engine behind `bat`, `delta`, and `xi-editor`. Includes guardrails for large inputs, graceful fallback to plain text, and SSH-aware clipboard integration for the `/copy` command. <img width="1554" height="1014" alt="image" src="https://github.com/user-attachments/assets/38737a79-8717-4715-b857-94cf1ba59b85" /> <img width="2354" height="1374" alt="image" src="https://github.com/user-attachments/assets/25d30a00-c487-4af8-9cb6-63b0695a4be7" /> ## Problem Code blocks in the TUI (markdown responses and file diffs) render without syntax highlighting, making it hard to scan code at a glance. Users also have no way to pick a color theme that matches their terminal aesthetic. ## Mental model The highlighting system has three layers: 1. **Syntax engine** (`render::highlight`) -- a thin wrapper around syntect + two-face. It owns a process-global `SyntaxSet` (~250 grammars) and a `RwLock<Theme>` that can be swapped at runtime. All public entry points accept `(code, lang)` and return ratatui `Span`/`Line` vectors or `None` when the language is unrecognized or the input exceeds safety guardrails. 2. **Rendering consumers** -- `markdown_render` feeds fenced code blocks through the engine; `diff_render` highlights Add/Delete content as a whole file and Update hunks per-hunk (preserving parser state across hunk lines). Both callers fall back to plain unstyled text when the engine returns `None`. 3. **Theme lifecycle** -- at startup the config's `tui.theme` is resolved to a syntect `Theme` via `set_theme_override`. At runtime the `/theme` picker calls `set_syntax_theme` to swap themes live; on cancel it restores the snapshot taken at open. On confirm it persists `[tui] theme = "..."` to config.toml. ## Non-goals - Inline diff highlighting (word-level change detection within a line). - Semantic / LSP-backed highlighting. - Theme authoring tooling; users supply standard `.tmTheme` files. ## Tradeoffs | Decision | Upside | Downside | | ------------------------------------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------------------------------- | | syntect over tree-sitter / arborium | ~1 MB binary increase for ~250 grammars + 32 themes; battle-tested crate powering widely-used tools (`bat`, `delta`, `xi-editor`). tree-sitter would add ~12 MB for 20-30 languages or ~35 MB for full coverage. | Regex-based; less structurally accurate than tree-sitter for some languages (e.g. language injections like JS-in-HTML). | | Global `RwLock<Theme>` | Enables live `/theme` preview without threading Theme through every call site | Lock contention risk (mitigated: reads vastly outnumber writes, single UI thread) | | Skip background / italic / underline from themes | Terminal BG preserved, avoids ugly rendering on some themes | Themes that rely on these properties lose fidelity | | Guardrails: 512 KB / 10k lines | Prevents pathological stalls on huge diffs or pastes | Very large files render without color | ## Architecture ``` config.toml ─[tui.theme]─> set_theme_override() ─> THEME (RwLock) │ ┌───────────────────────────────────────────┘ │ markdown_render ─── highlight_code_to_lines(code, lang) ─> Vec<Line> diff_render ─── highlight_code_to_styled_spans(code, lang) ─> Option<Vec<Vec<Span>>> │ │ (None ⇒ plain text fallback) │ /theme picker ─── set_syntax_theme(theme) // live preview swap ─── current_syntax_theme() // snapshot for cancel ─── resolve_theme_by_name(name) // lookup by kebab-case ``` Key files: - `tui/src/render/highlight.rs` -- engine, theme management, guardrails - `tui/src/diff_render.rs` -- syntax-aware diff line wrapping - `tui/src/theme_picker.rs` -- `/theme` command builder - `tui/src/bottom_pane/list_selection_view.rs` -- side content panel, callbacks - `core/src/config/types.rs` -- `Tui::theme` field - `core/src/config/edit.rs` -- `syntax_theme_edit()` helper ## Observability - `tracing::warn` when a configured theme name cannot be resolved. - `Config::startup_warnings` surfaces the same message as a TUI banner. - `tracing::error` when persisting theme selection fails. ## Tests - Unit tests in `highlight.rs`: language coverage, fallback behavior, CRLF stripping, style conversion, guardrail enforcement, theme name mapping exhaustiveness. - Unit tests in `diff_render.rs`: snapshot gallery at multiple terminal sizes (80x24, 94x35, 120x40), syntax-highlighted wrapping, large-diff guardrail, rename-to-different-extension highlighting, parser state preservation across hunk lines. - Unit tests in `theme_picker.rs`: preview rendering (wide + narrow), dim overlay on deletions, subtitle truncation, cancel-restore, fallback for unavailable configured theme. - Unit tests in `list_selection_view.rs`: side layout geometry, stacked fallback, buffer clearing, cancel/selection-changed callbacks. - Integration test in `lib.rs`: theme warning uses the final (post-resume) config. ## Cargo Deny: Unmaintained Dependency Exceptions This PR adds two `cargo deny` advisory exceptions for transitive dependencies pulled in by `syntect v5.3.0`: | Advisory | Crate | Status | |----------|-------|--------| | RUSTSEC-2024-0320 | `yaml-rust` | Unmaintained (maintainer unreachable) | | RUSTSEC-2025-0141 | `bincode` | Unmaintained (development ceased; v1.3.3 considered complete) | **Why this is safe in our usage:** - Neither advisory describes a known security vulnerability. Both are "unmaintained" notices only. - `bincode` is used by syntect to deserialize pre-compiled syntax sets. Again, these are **static vendored artifacts** baked into the binary at build time. No user-supplied bincode data is ever deserialized. - Attack surface is zero for both crates; exploitation would require a supply-chain compromise of our own build artifacts. - These exceptions can be removed when syntect migrates to `yaml-rust2` and drops `bincode`, or when alternative crates are available upstream.
This commit is contained in:
Felipe Coury
@@ -278,6 +278,9 @@ pub struct Config {
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/// `current-dir`.
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pub tui_status_line: Option<Vec<String>>,
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/// Syntax highlighting theme override (kebab-case name).
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pub tui_theme: Option<String>,
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/// The directory that should be treated as the current working directory
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/// for the session. All relative paths inside the business-logic layer are
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/// resolved against this path.
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@@ -2120,6 +2123,7 @@ impl Config {
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.map(|t| t.alternate_screen)
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.unwrap_or_default(),
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tui_status_line: cfg.tui.as_ref().and_then(|t| t.status_line.clone()),
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tui_theme: cfg.tui.as_ref().and_then(|t| t.theme.clone()),
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otel: {
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let t: OtelConfigToml = cfg.otel.unwrap_or_default();
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let log_user_prompt = t.log_user_prompt.unwrap_or(false);
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@@ -2518,6 +2522,30 @@ allowed_domains = ["openai.com"]
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Ok(())
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}
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#[test]
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fn tui_theme_deserializes_from_toml() {
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let cfg = r#"
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[tui]
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theme = "dracula"
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"#;
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let parsed =
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toml::from_str::<ConfigToml>(cfg).expect("TOML deserialization should succeed");
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assert_eq!(
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parsed.tui.as_ref().and_then(|t| t.theme.as_deref()),
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Some("dracula"),
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);
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}
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#[test]
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fn tui_theme_defaults_to_none() {
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let cfg = r#"
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[tui]
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"#;
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let parsed =
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toml::from_str::<ConfigToml>(cfg).expect("TOML deserialization should succeed");
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assert_eq!(parsed.tui.as_ref().and_then(|t| t.theme.as_deref()), None);
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}
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#[test]
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fn tui_config_missing_notifications_field_defaults_to_enabled() {
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let cfg = r#"
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@@ -2537,6 +2565,7 @@ allowed_domains = ["openai.com"]
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show_tooltips: true,
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alternate_screen: AltScreenMode::Auto,
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status_line: None,
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theme: None,
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}
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);
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}
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@@ -4646,6 +4675,7 @@ model_verbosity = "high"
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feedback_enabled: true,
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tui_alternate_screen: AltScreenMode::Auto,
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tui_status_line: None,
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tui_theme: None,
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otel: OtelConfig::default(),
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},
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o3_profile_config
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@@ -4768,6 +4798,7 @@ model_verbosity = "high"
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feedback_enabled: true,
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tui_alternate_screen: AltScreenMode::Auto,
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tui_status_line: None,
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tui_theme: None,
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otel: OtelConfig::default(),
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};
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@@ -4888,6 +4919,7 @@ model_verbosity = "high"
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feedback_enabled: true,
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tui_alternate_screen: AltScreenMode::Auto,
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tui_status_line: None,
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tui_theme: None,
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otel: OtelConfig::default(),
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};
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@@ -4994,6 +5026,7 @@ model_verbosity = "high"
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feedback_enabled: true,
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tui_alternate_screen: AltScreenMode::Auto,
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tui_status_line: None,
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tui_theme: None,
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otel: OtelConfig::default(),
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};
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