Check for the index.html file before trying to opener::open it

src/cmd/build.rs

@@ -1,7 +1,8 @@
-use crate::{get_book_dir, open};
+use crate::{first_chapter, get_book_dir, open};
 use clap::{arg, App, Arg, ArgMatches};
 use mdbook::errors::Result;
 use mdbook::MDBook;
+use std::path::Path;
 
 // Create clap subcommand arguments
 pub fn make_subcommand<'help>() -> App<'help> {
@@ -38,7 +39,15 @@ pub fn execute(args: &ArgMatches) -> Result<()> {
 
     if args.is_present("open") {
         // FIXME: What's the right behaviour if we don't use the HTML renderer?
-        open(book.build_dir_for("html").join("index.html"));
+        match first_chapter(&book)
+            .map(|path| book.build_dir_for("html").join(path).with_extension("html"))
+        {
+            Some(path) if Path::new(&path).exists() => open(path),
+            _ => {
+                error!("No chapter available to open");
+                std::process::exit(1)
+            }
+        }
     }
 
     Ok(())

src/cmd/serve.rs

@@ -1,6 +1,6 @@
 #[cfg(feature = "watch")]
 use super::watch;
-use crate::{get_book_dir, open};
+use crate::{first_chapter, get_book_dir, open};
 use clap::{arg, App, Arg, ArgMatches};
 use futures_util::sink::SinkExt;
 use futures_util::StreamExt;
@@ -102,10 +102,12 @@ pub fn execute(args: &ArgMatches) -> Result<()> {
         serve(build_dir, sockaddr, reload_tx, &file_404);
     });
 
-    let serving_url = format!("http://{}", address);
-    info!("Serving on: {}", serving_url);
-
     if open_browser {
+        let serving_url = match first_chapter(&book).map(|path| path.with_extension("html")) {
+            Some(path) => format!("http://{}/{}", address, path.display()),
+            _ => format!("http://{}", address),
+        };
+        info!("Serving on: {}", serving_url);
         open(serving_url);
     }
 

src/cmd/watch.rs

@@ -1,3 +1,4 @@
+use crate::first_chapter;
 use crate::{get_book_dir, open};
 use clap::{arg, App, Arg, ArgMatches};
 use mdbook::errors::Result;
@@ -45,7 +46,12 @@ pub fn execute(args: &ArgMatches) -> Result<()> {
 
     if args.is_present("open") {
         book.build()?;
-        open(book.build_dir_for("html").join("index.html"));
+        match first_chapter(&book)
+            .map(|path| book.build_dir_for("html").join(path).with_extension("html"))
+        {
+            Some(path) if Path::new(&path).exists() => open(path),
+            _ => warn!("No chapter available to open"),
+        }
     }
 
     trigger_on_change(&book, |paths, book_dir| {

src/main.rs

@@ -9,7 +9,10 @@ use clap::{App, AppSettings, Arg, ArgMatches};
 use clap_complete::Shell;
 use env_logger::Builder;
 use log::LevelFilter;
+use mdbook::book::Chapter;
 use mdbook::utils;
+use mdbook::BookItem;
+use mdbook::MDBook;
 use std::env;
 use std::ffi::OsStr;
 use std::io::Write;
@@ -137,6 +140,17 @@ fn get_book_dir(args: &ArgMatches) -> PathBuf {
     }
 }
 
+// Return the first displayable chapter of the given book, or None if no displayable
+// chapter is found (i.e. only drafts).
+fn first_chapter(book: &MDBook) -> Option<&PathBuf> {
+    book.iter().find_map(|item| match item {
+        BookItem::Chapter(Chapter {
+            path: Some(path), ..
+        }) => Some(path),
+        _ => None,
+    })
+}
+
 fn open<P: AsRef<OsStr>>(path: P) {
     info!("Opening web browser");
     if let Err(e) = opener::open(path) {