From c0d79f4c42ad85c5b983dad6d38e16801015da39 Mon Sep 17 00:00:00 2001
From: benmandrew <benmandrew@gmail.com>
Date: Wed, 21 Oct 2026 00:07:16 +0100
Subject: [PATCH] feat: add --no-preamble to omit the markup definitions

The output always defines diff-added and diff-deleted, so a caller that
wants its own styling has to strip them from every file. With
--no-preamble they are left out, and the caller imports its own
definitions. render() is unchanged; render_body() returns the body.
---
 README.md            |  3 ++-
 src/main.rs          | 10 +++++++++-
 src/render.rs        |  8 ++++++--
 tests/integration.rs | 14 +++++++++++++-
 4 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index 0e7ee93..1f433c4 100644
--- a/README.md
+++ b/README.md
@@ -90,7 +90,7 @@ cargo install --git https://github.com/sou1118/typdiff
 ## Usage
 
 ```
-typdiff <OLD> <NEW> [-o <OUTPUT>]
+typdiff <OLD> <NEW> [-o <OUTPUT>] [--no-preamble]
 ```
 
 | Argument | Description |
@@ -98,6 +98,7 @@ typdiff <OLD> <NEW> [-o <OUTPUT>]
 | `<OLD>` | Path to the old Typst file |
 | `<NEW>` | Path to the new Typst file |
 | `-o, --output <OUTPUT>` | Output file path (defaults to stdout) |
+| `--no-preamble` | Omit the definitions of `diff-added` and `diff-deleted`, so the output can import its own |
 
 ### Examples
 
diff --git a/src/main.rs b/src/main.rs
index c573d4f..d35f278 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -18,6 +18,10 @@ struct Cli {
     /// Output file path (defaults to stdout)
     #[arg(short, long)]
     output: Option<String>,
+
+    /// Omit the definitions of diff-added and diff-deleted from the output
+    #[arg(long)]
+    no_preamble: bool,
 }
 
 fn main() -> Result<()> {
@@ -39,7 +43,11 @@ fn main() -> Result<()> {
 
     let diff_results = typdiff::diff::diff(&old_blocks, &new_blocks);
 
-    let output = typdiff::render::render(&diff_results);
+    let output = if cli.no_preamble {
+        typdiff::render::render_body(&diff_results)
+    } else {
+        typdiff::render::render(&diff_results)
+    };
 
     match cli.output {
         Some(path) => {
diff --git a/src/render.rs b/src/render.rs
index 37a775a..59a0d9f 100644
--- a/src/render.rs
+++ b/src/render.rs
@@ -14,9 +14,13 @@ const PREAMBLE: &str = r##"#let diff-added(body) = {
 
 /// Render a list of diff results into a compilable Typst source string.
 pub fn render(results: &[DiffResult]) -> String {
+    format!("{PREAMBLE}\n{}", render_body(results))
+}
+
+/// Render diff results without the preamble that defines `diff-added` and
+/// `diff-deleted`. The caller must make those functions available.
+pub fn render_body(results: &[DiffResult]) -> String {
     let mut out = String::new();
-    out.push_str(PREAMBLE);
-    out.push('\n');
 
     for result in results {
         match result {
diff --git a/tests/integration.rs b/tests/integration.rs
index dacad43..403994a 100644
--- a/tests/integration.rs
+++ b/tests/integration.rs
@@ -1,6 +1,6 @@
 use typdiff::diff::diff;
 use typdiff::parse::parse;
-use typdiff::render::render;
+use typdiff::render::{render, render_body};
 
 fn run_diff(old: &str, new: &str) -> String {
     let old_blocks: Vec<_> = parse(old)
@@ -209,3 +209,15 @@ fn test_indented_line_comment_does_not_split_paragraph() {
     // A whitespace-only line would be treated as a paragraph break by Typst.
     assert!(!output.contains("\n  \n"));
 }
+
+#[test]
+fn test_render_body_omits_preamble() {
+    let old_blocks = parse("Old text.\n");
+    let new_blocks = parse("New text.\n");
+    let output = render_body(&diff(&old_blocks, &new_blocks));
+
+    // The caller imports its own definitions, which a preamble would shadow.
+    assert!(!output.contains("#let diff-added"));
+    assert!(!output.contains("#let diff-deleted"));
+    assert!(output.contains("#diff-added[New]"));
+}