ADR-0022 stage 2/8: input panel — token-class highlighting

New `input_render` module with `render_input_runs(input,
cursor_byte, theme) -> Vec<StyledRun>`. Lexes the input,
assigns each token its `theme.token_color`, preserves
whitespace gaps as `theme.fg` runs, and injects the cursor
by splitting the run that contains it into before/under/after
sub-spans (under marked Modifier::REVERSED). End-of-input
cursor is an empty-range sentinel rendered as an inverted
space.

ui::render_input_panel switches over EffectiveMode: simple
mode goes through render_input_runs + a small runs_to_spans
helper that borrows from the input string; advanced modes
(persistent + one-shot `:`) keep the previous plain
before/under/after rendering since the DSL lexer doesn't
speak SQL (ADR-0022 §12).

Multi-byte UTF-8 in string literals is handled by walking
to the next char boundary when splitting the cursor run,
mirroring the previous renderer.

Tests: 682 passing, 0 failing, 1 ignored (672 baseline →
+10: 9 input_render unit tests covering each token class,
cursor placements, multi-byte, full-command shape; +1 new
"all token classes" UI snapshot). Clippy clean.

Caveat (noted inline in the new snapshot test): the
TestBackend/render_to_string path records text symbols
only, not ratatui style. The new snapshot is therefore a
text-layout regression net; the unit tests in
input_render::tests are the authoritative regression net
for colour mappings.

Stage 3 wires the same colouring into simple-mode echo
lines in the output panel.

src/input_render.rs

@@ -0,0 +1,269 @@
+//! Render-side helpers for the input panel
+//! (ADR-0022 stage 2 — token-class colouring of the live
+//! input field with cursor injection).
+//!
+//! The functions here are pure: given an input string, a
+//! cursor byte position, and a theme, they return a sequence
+//! of `StyledRun`s describing each contiguous span with its
+//! ratatui style. `ui::render_input_panel` converts these to
+//! `Span<'_>`s at render time.
+//!
+//! Cursor handling:
+//!   - Cursor inside a token splits that token's run into
+//!     before/under/after, with `under` carrying the token's
+//!     colour plus `Modifier::REVERSED`.
+//!   - Cursor on a whitespace gap between tokens splits the
+//!     gap the same way.
+//!   - Cursor at end-of-input is represented as a trailing
+//!     run with empty byte range; the renderer treats that as
+//!     "inverted space".
+//!
+//! Per ADR-0022 §2/§3, this is the silent always-on layer.
+//! The error overlay (stage 4) and hint panel (stage 5)
+//! compose with these runs without fighting them.
+
+use ratatui::style::{Modifier, Style};
+
+use crate::dsl::lexer::lex;
+use crate::theme::Theme;
+
+/// A run of text with its byte range in the source and the
+/// ratatui style it should render with. The text itself is
+/// not stored — callers slice `source[byte_range.0..byte_range.1]`.
+///
+/// An empty byte range (`(n, n)`) represents the end-of-input
+/// cursor and is rendered as an inverted space.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct StyledRun {
+    pub byte_range: (usize, usize),
+    pub style: Style,
+}
+
+impl StyledRun {
+    /// The text this run covers in `source`. Empty for the
+    /// end-of-input cursor sentinel.
+    #[must_use]
+    pub fn text<'a>(&self, source: &'a str) -> &'a str {
+        &source[self.byte_range.0..self.byte_range.1]
+    }
+}
+
+/// Build the run sequence for the input panel.
+///
+/// Lexes `input`, assigns each token its `theme.token_color`,
+/// preserves whitespace gaps as `theme.fg` runs, then injects
+/// the cursor at `cursor_byte` (clamped to `input.len()`).
+#[must_use]
+pub fn render_input_runs(input: &str, cursor_byte: usize, theme: &Theme) -> Vec<StyledRun> {
+    let mut runs = base_runs(input, theme);
+    inject_cursor(&mut runs, input, cursor_byte, theme);
+    runs
+}
+
+fn base_runs(input: &str, theme: &Theme) -> Vec<StyledRun> {
+    let tokens = lex(input);
+    let mut runs = Vec::with_capacity(tokens.len() * 2);
+    let mut pos = 0;
+    for tok in tokens {
+        let (start, end) = tok.span;
+        if pos < start {
+            // Whitespace gap before this token.
+            runs.push(StyledRun {
+                byte_range: (pos, start),
+                style: Style::default().fg(theme.fg),
+            });
+        }
+        runs.push(StyledRun {
+            byte_range: (start, end),
+            style: Style::default().fg(theme.token_color(&tok.kind)),
+        });
+        pos = end;
+    }
+    if pos < input.len() {
+        runs.push(StyledRun {
+            byte_range: (pos, input.len()),
+            style: Style::default().fg(theme.fg),
+        });
+    }
+    runs
+}
+
+fn inject_cursor(
+    runs: &mut Vec<StyledRun>,
+    input: &str,
+    cursor_byte: usize,
+    theme: &Theme,
+) {
+    let cursor_byte = cursor_byte.min(input.len());
+
+    // End-of-input cursor: append the empty-range sentinel.
+    if cursor_byte == input.len() {
+        runs.push(StyledRun {
+            byte_range: (input.len(), input.len()),
+            style: Style::default()
+                .fg(theme.fg)
+                .add_modifier(Modifier::REVERSED),
+        });
+        return;
+    }
+
+    let idx = runs
+        .iter()
+        .position(|r| r.byte_range.0 <= cursor_byte && cursor_byte < r.byte_range.1)
+        .expect("cursor_byte < input.len() ⇒ some run contains it");
+    let target = runs[idx].clone();
+    let (start, end) = target.byte_range;
+
+    // Walk to the next char boundary so a multi-byte UTF-8
+    // codepoint is treated as a single visual unit at the
+    // cursor.
+    let mut char_end = cursor_byte + 1;
+    while char_end < input.len() && !input.is_char_boundary(char_end) {
+        char_end += 1;
+    }
+
+    let mut replacement: Vec<StyledRun> = Vec::with_capacity(3);
+    if start < cursor_byte {
+        replacement.push(StyledRun {
+            byte_range: (start, cursor_byte),
+            style: target.style,
+        });
+    }
+    replacement.push(StyledRun {
+        byte_range: (cursor_byte, char_end),
+        style: target.style.add_modifier(Modifier::REVERSED),
+    });
+    if char_end < end {
+        replacement.push(StyledRun {
+            byte_range: (char_end, end),
+            style: target.style,
+        });
+    }
+
+    runs.splice(idx..=idx, replacement);
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use pretty_assertions::assert_eq;
+
+    fn dark() -> Theme {
+        Theme::dark()
+    }
+
+    fn reversed(r: &StyledRun) -> bool {
+        r.style.add_modifier.contains(Modifier::REVERSED)
+    }
+
+    #[test]
+    fn empty_input_renders_only_the_end_of_input_cursor() {
+        let runs = render_input_runs("", 0, &dark());
+        assert_eq!(runs.len(), 1);
+        assert_eq!(runs[0].byte_range, (0, 0));
+        assert!(reversed(&runs[0]));
+    }
+
+    #[test]
+    fn keyword_token_takes_keyword_colour() {
+        let theme = dark();
+        let runs = render_input_runs("create", 6, &theme);
+        // Token + end-of-input cursor.
+        assert_eq!(runs.len(), 2);
+        assert_eq!(runs[0].byte_range, (0, 6));
+        assert_eq!(runs[0].style.fg, Some(theme.tok_keyword));
+        assert!(!reversed(&runs[0]));
+        assert!(reversed(&runs[1]));
+    }
+
+    #[test]
+    fn cursor_inside_token_splits_into_three_runs_keeping_colour() {
+        let theme = dark();
+        let runs = render_input_runs("create", 3, &theme);
+        assert_eq!(runs.len(), 3);
+        assert_eq!(runs[0].byte_range, (0, 3));
+        assert_eq!(runs[1].byte_range, (3, 4));
+        assert_eq!(runs[2].byte_range, (4, 6));
+        // All three keep the keyword colour.
+        for r in &runs {
+            assert_eq!(r.style.fg, Some(theme.tok_keyword));
+        }
+        assert!(!reversed(&runs[0]));
+        assert!(reversed(&runs[1]));
+        assert!(!reversed(&runs[2]));
+    }
+
+    #[test]
+    fn cursor_on_whitespace_inverts_a_single_space() {
+        let theme = dark();
+        // "create table" has whitespace at byte 6.
+        let runs = render_input_runs("create table", 6, &theme);
+        // base: keyword, ws(6,7), keyword. After cursor injection
+        // at the start of ws: under=(6,7) REVERSED. The
+        // before/after slices are empty so we get 3 runs total.
+        assert_eq!(runs.len(), 3);
+        let r_under: Vec<_> = runs.iter().filter(|r| reversed(r)).collect();
+        assert_eq!(r_under.len(), 1);
+        assert_eq!(r_under[0].byte_range, (6, 7));
+        assert_eq!(r_under[0].style.fg, Some(theme.fg));
+    }
+
+    #[test]
+    fn lex_error_token_renders_in_error_colour() {
+        let theme = dark();
+        let runs = render_input_runs("$", 1, &theme);
+        // Error token (0,1), then end-of-input cursor (1,1).
+        assert_eq!(runs.len(), 2);
+        assert_eq!(runs[0].style.fg, Some(theme.tok_error));
+    }
+
+    #[test]
+    fn whitespace_between_tokens_takes_default_fg() {
+        let theme = dark();
+        let runs = render_input_runs("create table", 12, &theme);
+        // base: keyword(0,6), ws(6,7), keyword(7,12). Plus
+        // end-of-input cursor (12,12) = 4 runs.
+        assert_eq!(runs.len(), 4);
+        assert_eq!(runs[1].byte_range, (6, 7));
+        assert_eq!(runs[1].style.fg, Some(theme.fg));
+        assert_eq!(runs[3].byte_range, (12, 12));
+        assert!(reversed(&runs[3]));
+    }
+
+    #[test]
+    fn cursor_inside_multi_byte_string_literal_advances_to_char_boundary() {
+        let theme = dark();
+        // 'café' = ['(0)', c(1), a(2), f(3), é(4-5), '(6)] — é is 2 bytes.
+        // Cursor at byte 4: inside é. char_end advances to 6.
+        let runs = render_input_runs("'café'", 4, &theme);
+        let r_under: Vec<_> = runs.iter().filter(|r| reversed(r)).collect();
+        assert_eq!(r_under.len(), 1);
+        assert_eq!(r_under[0].byte_range, (4, 6));
+    }
+
+    #[test]
+    fn end_of_input_cursor_is_an_empty_range() {
+        let runs = render_input_runs("create", 6, &dark());
+        let last = runs.last().expect("non-empty");
+        assert_eq!(last.byte_range, (6, 6));
+        assert!(reversed(last));
+    }
+
+    #[test]
+    fn full_command_lexes_to_each_token_class() {
+        let theme = dark();
+        let runs = render_input_runs(
+            "insert into T values (1, 'hi', null) --all-rows",
+            47,
+            &theme,
+        );
+        // Spot-check: there's at least one run of each token class.
+        let fgs: Vec<_> = runs.iter().filter_map(|r| r.style.fg).collect();
+        assert!(fgs.contains(&theme.tok_keyword)); // insert / into / values / null
+        assert!(fgs.contains(&theme.tok_identifier)); // T / hi (string is separate)
+        assert!(fgs.contains(&theme.tok_number)); // 1
+        assert!(fgs.contains(&theme.tok_string)); // 'hi'
+        assert!(fgs.contains(&theme.tok_punct)); // ( , )
+        assert!(fgs.contains(&theme.tok_flag)); // --all-rows
+    }
+}

src/lib.rs

@@ -13,6 +13,7 @@ pub mod db;
 pub mod dsl;
 pub mod event;
 pub mod friendly;
+pub mod input_render;
 pub mod logging;
 pub mod mode;
 pub mod output_render;

src/snapshots/rdbms_playground__ui__tests__highlighted_input_all_token_classes_dark.snap

@@ -0,0 +1,28 @@
+---
+source: src/ui.rs
+expression: snapshot
+---
+╭ Tables ──────────────────╮╭ Output ──────────────────────────────────────────╮
+│(none yet)                ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          ││                                                  │
+│                          │╰──────────────────────────────────────────────────╯
+│                          │╭ SIMPLE ──────────────────────────────────────────╮
+│                          ││insert into T values (1, 'hi', null) --all-rows $ │
+│                          │╰──────────────────────────────────────────────────╯
+│                          │╭ Hint ────────────────────────────────────────────╮
+│                          ││(no active hint)                                  │
+╰──────────────────────────╯╰──────────────────────────────────────────────────╯
+Project: Term Planner                                                           
+Enter submit  ·  : advanced once  ·  mode advanced switch  ·  Ctrl-C quit

src/ui.rs

@@ -580,30 +580,67 @@ fn render_input_panel(app: &App, theme: &Theme, frame: &mut Frame<'_>, area: Rec
 
     // Cursor block: render the character at the cursor position
     // inverted so the cursor is visible without enabling a real
-    // terminal cursor. When the cursor is at end-of-input we
-    // append an inverted space.
+    // terminal cursor.
+    //
+    // Simple-mode input gets per-token colouring (ADR-0022 §3)
+    // via input_render::render_input_runs. Advanced-mode input
+    // — DSL lexer doesn't speak SQL — renders plain (§12), with
+    // the same before/under/after cursor shape we always had.
     let cursor = app.input_cursor.min(app.input.len());
-    let before = &app.input[..cursor];
-    let (under, after) = if cursor < app.input.len() {
-        // Find the end of the character under the cursor.
+    let spans = match effective {
+        EffectiveMode::Simple => {
+            let runs = crate::input_render::render_input_runs(&app.input, cursor, theme);
+            runs_to_spans(&app.input, &runs)
+        }
+        EffectiveMode::AdvancedPersistent | EffectiveMode::AdvancedOneShot => {
+            plain_input_spans(&app.input, cursor, theme)
+        }
+    };
+    let paragraph = Paragraph::new(Line::from(spans)).block(block);
+    frame.render_widget(paragraph, area);
+}
+
+/// Convert `StyledRun`s into ratatui `Span`s borrowed from
+/// `input`. The end-of-input cursor sentinel (empty range) is
+/// rendered as an inverted space.
+fn runs_to_spans<'a>(
+    input: &'a str,
+    runs: &[crate::input_render::StyledRun],
+) -> Vec<Span<'a>> {
+    runs.iter()
+        .map(|r| {
+            if r.byte_range.0 == r.byte_range.1 {
+                Span::styled(" ", r.style)
+            } else {
+                Span::styled(&input[r.byte_range.0..r.byte_range.1], r.style)
+            }
+        })
+        .collect()
+}
+
+/// Plain (no token highlighting) input rendering for advanced
+/// mode. Same before/under/after cursor shape as the
+/// pre-ADR-0022 input panel; here as a deliberate fallback.
+fn plain_input_spans<'a>(input: &'a str, cursor: usize, theme: &Theme) -> Vec<Span<'a>> {
+    let cursor = cursor.min(input.len());
+    let before = &input[..cursor];
+    let (under, after) = if cursor < input.len() {
         let mut end = cursor + 1;
-        while end < app.input.len() && !app.input.is_char_boundary(end) {
+        while end < input.len() && !input.is_char_boundary(end) {
             end += 1;
         }
-        (&app.input[cursor..end], &app.input[end..])
+        (&input[cursor..end], &input[end..])
     } else {
         (" ", "")
     };
-    let spans = vec![
+    vec![
         Span::styled(before, Style::default().fg(theme.fg)),
         Span::styled(
             under,
             Style::default().fg(theme.fg).add_modifier(Modifier::REVERSED),
         ),
         Span::styled(after, Style::default().fg(theme.fg)),
-    ];
-    let paragraph = Paragraph::new(Line::from(spans)).block(block);
-    frame.render_widget(paragraph, area);
+    ]
 }
 
 fn render_hint_panel(app: &App, theme: &Theme, frame: &mut Frame<'_>, area: Rect) {
@@ -731,6 +768,26 @@ mod tests {
         insta::assert_snapshot!("default_advanced_dark", snapshot);
     }
 
+    #[test]
+    fn highlighted_input_all_token_classes_snapshot() {
+        // ADR-0022 stage 2: representative input that exercises
+        // every token class — keyword (insert / into / values
+        // / null), identifier (T), number (1), string ('hi'),
+        // punct (parens, comma), flag (--all-rows), lex error
+        // ($ at the end). The snapshot captures the rendered
+        // text symbols only — `render_to_string` does not record
+        // ratatui style — so this test is a regression net for
+        // text layout, not for colour mappings. Colour mappings
+        // are unit-tested in `input_render::tests`.
+        let mut app = App::new();
+        app.input
+            .push_str("insert into T values (1, 'hi', null) --all-rows $");
+        app.input_cursor = app.input.len();
+        let theme = Theme::dark();
+        let snapshot = render_to_string(&mut app, &theme, 80, 24);
+        insta::assert_snapshot!("highlighted_input_all_token_classes_dark", snapshot);
+    }
+
     #[test]
     fn one_shot_advanced_prompt_snapshot() {
         // Typing `:sel` in simple mode should flip the input panel