feat(styling): add TOML syntax highlighting for gutter output (#905)

* feat(styling): add TOML syntax highlighting for gutter output

Add format_toml() with syntax highlighting for config previews:
- Table headers [section] in cyan bold
- String values in green
- Comments dimmed

Update show-theme to demonstrate all three gutter styles:
- Error details (plain text)
- Config (TOML highlighted)
- Shell code (bash highlighted)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix(styling): add trailing newline after format_toml in config show

The format_toml change to remove trailing newlines broke config show
output. Use writeln! instead of write! to restore the blank line
between sections.

Co-Authored-By: Claude <noreply@anthropic.com>

* refactor(styling): simplify format_toml token handling

Merge TokOpt::Some and TokOpt::None branches to share the unstyled
path. Synoptic's TOML highlighter returns TokOpt::None for unstyled
content (keys, operators, whitespace), not TokOpt::Some with unrecognized
types.

Add test verifying both styled and unstyled paths are exercised.

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: max-sixty

src/commands/config/show.rs

@@ -402,7 +402,7 @@ fn render_user_config(out: &mut String) -> anyhow::Result<()> {
     }
 
     // Display TOML with syntax highlighting (gutter at column 0)
-    write!(out, "{}", format_toml(&contents))?;
+    writeln!(out, "{}", format_toml(&contents))?;
 
     Ok(())
 }
@@ -523,7 +523,7 @@ fn render_project_config(out: &mut String) -> anyhow::Result<()> {
     }
 
     // Display TOML with syntax highlighting (gutter at column 0)
-    write!(out, "{}", format_toml(&contents))?;
+    writeln!(out, "{}", format_toml(&contents))?;
 
     Ok(())
 }

src/commands/configure_shell.rs

@@ -7,8 +7,8 @@ use anstyle::Style;
 use worktrunk::path::format_path_for_display;
 use worktrunk::shell::{self, Shell};
 use worktrunk::styling::{
-    INFO_SYMBOL, SUCCESS_SYMBOL, eprint, eprintln, format_bash_with_gutter, format_with_gutter,
-    prompt_message, warning_message,
+    INFO_SYMBOL, SUCCESS_SYMBOL, eprint, eprintln, format_bash_with_gutter, format_toml,
+    format_with_gutter, prompt_message, warning_message,
 };
 
 use crate::output::prompt::{PromptResponse, prompt_yes_no_preview};
@@ -1246,19 +1246,25 @@ pub fn handle_show_theme() {
 
     eprintln!();
 
-    // Gutter - quoted content
-    eprintln!("{}", info_message("Gutter formatting (quoted content):"));
+    // Gutter - error details (plain text, no syntax highlighting)
+    eprintln!("{}", info_message("Gutter formatting (error details):"));
     eprintln!(
         "{}",
-        format_with_gutter(
-            "[commit-generation]\ncommand = \"llm --model claude\"",
-            None,
-        )
+        format_with_gutter("expected `=`, found newline at line 3 column 1", None,)
     );
 
     eprintln!();
 
-    // Gutter - bash code
+    // Gutter - TOML config (syntax highlighted)
+    eprintln!("{}", info_message("Gutter formatting (config):"));
+    eprintln!(
+        "{}",
+        format_toml("[commit.generation]\ncommand = \"llm --model claude\"")
+    );
+
+    eprintln!();
+
+    // Gutter - bash code (syntax highlighted)
     eprintln!("{}", info_message("Gutter formatting (shell code):"));
     eprintln!(
         "{}",

src/output/commit_generation.rs

@@ -8,9 +8,7 @@ use std::io::{self, IsTerminal};
 
 use color_print::cformat;
 use worktrunk::config::UserConfig;
-use worktrunk::styling::{
-    eprintln, format_with_gutter, hint_message, info_message, success_message,
-};
+use worktrunk::styling::{eprintln, format_toml, hint_message, info_message, success_message};
 
 use super::prompt::{PromptResponse, prompt_yes_no_preview};
 
@@ -146,7 +144,7 @@ pub fn prompt_commit_generation(config: &mut UserConfig) -> anyhow::Result<bool>
                     "Would add to <bold>~/.config/worktrunk/config.toml</>:"
                 ))
             );
-            eprintln!("{}", format_with_gutter(&config_preview, None));
+            eprintln!("{}", format_toml(&config_preview));
             eprintln!();
         },
     )?;
@@ -168,7 +166,7 @@ pub fn prompt_commit_generation(config: &mut UserConfig) -> anyhow::Result<bool>
 
             // Show what was added
             eprintln!("{}", success_message(cformat!("Added to user config:")));
-            eprintln!("{}", format_with_gutter(&config_preview, None));
+            eprintln!("{}", format_toml(&config_preview));
             eprintln!(
                 "{}",
                 hint_message(cformat!("View config: <bright-black>wt config show</>"))

src/styling/highlighting.rs

@@ -87,6 +87,9 @@ pub(super) fn bash_token_style(kind: &str) -> Option<Style> {
 // ============================================================================
 
 /// Formats TOML content with syntax highlighting using synoptic
+///
+/// Returns formatted output without trailing newline (consistent with format_with_gutter
+/// and format_bash_with_gutter).
 pub fn format_toml(content: &str) -> String {
     // synoptic has built-in TOML support, so this always succeeds
     let mut highlighter = from_extension("toml", 4).expect("synoptic supports TOML");
@@ -97,29 +100,31 @@ pub fn format_toml(content: &str) -> String {
     highlighter.run(&lines);
 
     // Render each line with gutter and appropriate styling
-    let mut output = String::new();
-    for (y, line) in lines.iter().enumerate() {
-        output.push_str(&format!("{gutter} {gutter:#} "));
-
-        for token in highlighter.line(y, line) {
-            match token {
-                TokOpt::Some(text, kind) => {
-                    if let Some(s) = toml_token_style(&kind) {
-                        output.push_str(&format!("{s}{text}{s:#}"));
-                    } else {
-                        output.push_str(&text);
-                    }
-                }
-                TokOpt::None(text) => {
-                    output.push_str(&text);
+    // Build lines without trailing newline - caller is responsible for element separation
+    let output_lines: Vec<String> = lines
+        .iter()
+        .enumerate()
+        .map(|(y, line)| {
+            let mut line_output = format!("{gutter} {gutter:#} ");
+
+            for token in highlighter.line(y, line) {
+                let (text, style) = match token {
+                    TokOpt::Some(text, kind) => (text, toml_token_style(&kind)),
+                    TokOpt::None(text) => (text, None),
+                };
+
+                if let Some(s) = style {
+                    line_output.push_str(&format!("{s}{text}{s:#}"));
+                } else {
+                    line_output.push_str(&text);
                 }
             }
-        }
 
-        output.push('\n');
-    }
+            line_output
+        })
+        .collect();
 
-    output
+    output_lines.join("\n")
 }
 
 /// Maps TOML token kinds to anstyle styles
@@ -299,6 +304,44 @@ mod tests {
         assert!(result.lines().count() >= 2);
     }
 
+    #[test]
+    fn test_format_toml_has_styled_and_unstyled_text() {
+        // This test verifies that format_toml handles both styled tokens (string, table)
+        // and unstyled text (TokOpt::None for whitespace, punctuation)
+        use synoptic::{TokOpt, from_extension};
+
+        let content = "key = \"value\"";
+        let mut highlighter = from_extension("toml", 4).expect("synoptic supports TOML");
+        let lines: Vec<String> = content.lines().map(|s| s.to_string()).collect();
+        highlighter.run(&lines);
+
+        // Collect token types
+        let mut has_styled = false;
+        let mut has_unstyled = false;
+        for (y, line) in lines.iter().enumerate() {
+            for token in highlighter.line(y, line) {
+                match token {
+                    TokOpt::Some(_, kind) => {
+                        if toml_token_style(&kind).is_some() {
+                            has_styled = true;
+                        }
+                    }
+                    TokOpt::None(_) => {
+                        has_unstyled = true;
+                    }
+                }
+            }
+        }
+
+        // Should have styled token (the string "value")
+        assert!(has_styled, "Should have at least one styled token");
+        // Should have unstyled text (whitespace, "=", "key")
+        assert!(
+            has_unstyled,
+            "Should have at least one unstyled text segment"
+        );
+    }
+
     #[test]
     fn test_format_toml_multiline() {
         let content = "[table]\nkey1 = \"value1\"\nkey2 = 42\n# comment\nkey3 = false";

tests/integration_tests/snapshots/integration__integration_tests__config_show_theme__show_theme.snap

@@ -12,10 +12,13 @@ info:
     GIT_EDITOR: ""
     LANG: C
     LC_ALL: C
+    PSModulePath: ""
     RUST_LOG: warn
     SHELL: ""
     TERM: alacritty
     WORKTRUNK_CONFIG_PATH: /nonexistent/test/config.toml
+    WORKTRUNK_TEST_CLAUDE_INSTALLED: "0"
+    WORKTRUNK_TEST_POWERSHELL_ENV: "0"
     WORKTRUNK_TEST_SKIP_URL_HEALTH_CHECK: "1"
     WT_TEST_DELAYED_STREAM_MS: "-1"
     WT_TEST_EPOCH: "1735776000"
@@ -32,9 +35,12 @@ exit_code: 0
 ↳ To rebase onto main, run wt merge
 ○ Showing 5 worktrees
 
-○ Gutter formatting (quoted content):
-  [commit-generation]
-  command = "llm --model claude"
+○ Gutter formatting (error details):
+  expected `=`, found newline at line 3 column 1
+
+○ Gutter formatting (config):
+  [commit.generation]
+  command = "llm --model claude"
 
 ○ Gutter formatting (shell code):
   eval "$(wt config shell init bash)"