---
title: "Session: adding-syntax-highlighting — 2026-03-18"
type: source
tags: [claude-code, session-transcript, demo]
date: 2026-03-18
source_file: raw/sessions/demo-blog-engine/2026-03-18-adding-syntax-highlighting.md
sessionId: demo-000000000000000000000000000002
slug: adding-syntax-highlighting
project: demo-blog-engine
started: 2026-03-18T14:20:00+00:00
ended: 2026-03-18T16:05:42+00:00
cwd: /Users/demo/code/demo-blog-engine
gitBranch: feat/syntax-highlight
permissionMode: default
model: claude-sonnet-4-6
user_messages: 4
tool_calls: 12
tools_used: [Read, Edit, Bash, Grep]
tool_counts: {"Edit": 5, "Read": 4, "Bash": 2, "Grep": 1}
token_totals: {"input": 6100, "cache_creation": 9400, "cache_read": 22000, "output": 3100}
turn_count: 4
hour_buckets: {"2026-03-18T14": 6, "2026-03-18T15": 8, "2026-03-18T16": 2}
duration_seconds: 6342
is_subagent: false
---

# Session: adding-syntax-highlighting — 2026-03-18

**Project:** `demo-blog-engine` · **Branch:** `feat/syntax-highlight` · **Mode:** `default` · **Model:** `claude-sonnet-4-6`

## Summary

Added syntax highlighting to the blog via `syntect`. Wired it into the `pulldown-cmark` code-block callback so fenced code with a language hint gets inline-highlighted HTML. Chose the `base16-ocean.dark` theme as the default.

## Conversation

### Turn 1 — User

Add syntax highlighting to code blocks. Use `syntect`.

### Turn 1 — Assistant

Plan:
1. Add `syntect = "5"` to `Cargo.toml`
2. Load default syntax + theme sets once at startup
3. In the `pulldown-cmark` parser, intercept `Event::Start(CodeBlock)` and replace the body with `highlighted_html_for_string`

The tricky bit is that `pulldown-cmark` gives us the code as an `Event::Text` inside the code-block range, so we need to buffer events between `Start(CodeBlock(..))` and `End(CodeBlock)`, then emit a single `Html` event with the highlighted output.

**Tools used in this turn:**
- `Edit`: `Cargo.toml` — added `syntect = "5"`
- `Read`: `src/render.rs` (1–80)

### Turn 2 — User

Sounds right, go ahead.

### Turn 2 — Assistant

Wired it up. Using `ClassedHTMLGenerator` so we emit `class="syntect"` and style via an external CSS file rather than inline colours (plays nicer with dark-mode toggle later).

**Tools used in this turn:**
- `Edit`: `src/render.rs` — added `highlight_block()` helper
- `Bash`: `cargo build` — exit 0
- `Bash`: `cargo run` — exit 0

## Connections

- [[demo-blog-engine]] — project
- [[syntect]] — library
- [[pulldown-cmark]] — library
- [[SyntaxHighlighting]] — concept