Fix issue 832 (rust-lang#841)

* Add if around stub summary creation

Check if an existing SUMMARY.md is present to prevent overwriting it
with the stub SUMMARY.md.

[rust-lang#832]

* Add test for existing SUMMARY.md

src/book/init.rs

@@ -176,15 +176,19 @@ impl BookBuilder {
         let src_dir = self.root.join(&self.config.book.src);
 
         let summary = src_dir.join("SUMMARY.md");
-        let mut f = File::create(&summary).chain_err(|| "Unable to create SUMMARY.md")?;
-        writeln!(f, "# Summary")?;
-        writeln!(f)?;
-        writeln!(f, "- [Chapter 1](./chapter_1.md)")?;
-
-        let chapter_1 = src_dir.join("chapter_1.md");
-        let mut f = File::create(&chapter_1).chain_err(|| "Unable to create chapter_1.md")?;
-        writeln!(f, "# Chapter 1")?;
-
+        if !summary.exists() {
+            trace!("No summary found creating stub summary and chapter_1.md.");
+            let mut f = File::create(&summary).chain_err(|| "Unable to create SUMMARY.md")?;
+            writeln!(f, "# Summary")?;
+            writeln!(f)?;
+            writeln!(f, "- [Chapter 1](./chapter_1.md)")?;
+
+            let chapter_1 = src_dir.join("chapter_1.md");
+            let mut f = File::create(&chapter_1).chain_err(|| "Unable to create chapter_1.md")?;
+            writeln!(f, "# Chapter 1")?;
+        } else {
+            trace!("Existing summary found, no need to create stub files.");
+        }
         Ok(())
     }
 

tests/init.rs

@@ -4,6 +4,8 @@ extern crate tempfile;
 use mdbook::config::Config;
 use mdbook::MDBook;
 use std::fs;
+use std::fs::File;
+use std::io::prelude::*;
 use std::path::PathBuf;
 use tempfile::Builder as TempFileBuilder;
 
@@ -27,6 +29,36 @@ fn base_mdbook_init_should_create_default_content() {
     }
 }
 
+/// Run `mdbook init` in a directory containing a SUMMARY.md should create the
+/// files listed in the summary.
+#[test]
+fn run_mdbook_init_should_create_content_from_summary() {
+    let created_files = vec!["intro.md", "first.md", "outro.md"];
+
+    let temp = TempFileBuilder::new().prefix("mdbook").tempdir().unwrap();
+    let src_dir = temp.path().join("src");
+    fs::create_dir_all(src_dir.clone()).unwrap();
+    static SUMMARY: &'static str = r#"# Summary
+
+[intro](intro.md)
+
+- [First chapter](first.md)
+
+[outro](outro.md)
+
+"#;
+
+    let mut summary = File::create(src_dir.join("SUMMARY.md")).unwrap();
+    summary.write_all(SUMMARY.as_bytes()).unwrap();
+    MDBook::init(temp.path()).build().unwrap();
+
+    for file in &created_files {
+        let target = src_dir.join(file);
+        println!("{}", target.display());
+        assert!(target.exists(), "{} doesn't exist", file);
+    }
+}
+
 /// Set some custom arguments for where to place the source and destination
 /// files, then call `mdbook init`.
 #[test]