Use termion backend for cursive

With this patch, we replace cursive’s default ncurses backend with the
termion backend.  This has multiple reasons:
- The ncurses backend has safety issues, see [0].
- ncurses requires a pre-installed library and a C compiler, introducing
  additional build dependencies.  Termion is implemented in Rust only.
- ncurses does not work on Windows, while termion works in all terminals
  that support ANSI escape codes.

Per default, the termion backend does not buffer the output which may
cause flickering [1].  Therefore, we also use the
cursive_buffered_backend that buffers the output and fixes the
flickering problem.

[0] gyscos/cursive#488
[1] gyscos/cursive#142

Cargo.toml

@@ -19,7 +19,7 @@ exclude = [".builds/*", "tests/html/*", "tests/snapshots/*"]
 ansi_term = "0.12.1"
 anyhow = "1.0.31"
 atty = "0.2.14"
-cursive = "0.15.0"
+cursive_buffered_backend = "0.4"
 cursive-markup = "0.1"
 html2text = "0.2.1"
 kuchiki = "0.8.0"
@@ -36,6 +36,11 @@ url = "2.1.1"
 webbrowser = "0.5.5"
 xdg = "2.2.0"
 
+[dependencies.cursive]
+version = "0.15"
+default-features = false
+features = ["termion-backend"]
+
 [dependencies.env_logger]
 version = "0.7.1"
 default-features = false

INSTALL.md

@@ -16,23 +16,7 @@ rusty-man packages are available for these distributions:
 
 ### Build Requirements
 
-To compile rusty-man, you need Rust 1.40 or later.  The `tui` backend requires
-the ncurses library in the default search path and a C compiler.
-
-If you don’t want to use ncurses, you can select another [`cursive`][] backend
-by replacing this line in `Cargo.toml`:
-
-```toml
-cursive = "0.15.0"
-```
-
-with this:
-
-```toml
-cursive = { version = "0.15.0", default-features = false, feature = ["termion-backend"] }
-```
-
-[`cursive`]: https://lib.rs/cursive
+To compile rusty-man, you need Rust 1.40 or later.
 
 ### Installing from Git
 

README.md

@@ -72,10 +72,10 @@ information.  rusty-man is also available as a package for these distributions:
 - Arch Linux: [`rusty-man`][pkg-aur] in the Arch User Repository
 
 rusty-man is developed for Unix-like systems.  It should run on other platforms
-too, but with some limitations:  The `rich` viewer uses ANSI escape codes,
-which are not supported on older Windows versions.  The `tui` viewer requires
-the ncurses library.  If you have trouble running rusty-man on your platform or
-if you want to help porting rusty-man to other platforms, please let me know.
+too, but with some limitations:  The `rich` and `tui` viewers uses ANSI escape
+codes, which are not supported on older Windows versions.  If you have trouble
+running rusty-man on your platform or if you want to help porting rusty-man to
+other platforms, please let me know.
 
 ## Integrations
 

src/viewer/tui/mod.rs

@@ -189,11 +189,19 @@ fn indent_view<V>(indent: impl Into<usize>, view: V) -> PaddedView<V> {
     PaddedView::lrtb(indent.into(), 0, 0, 0, view)
 }
 
+fn create_backend() -> anyhow::Result<Box<dyn cursive::backend::Backend>> {
+    let termion =
+        cursive::backends::termion::Backend::init().context("Could not create termion backend")?;
+    let buffered = cursive_buffered_backend::BufferedBackend::new(termion);
+    Ok(Box::new(buffered))
+}
+
 fn create_cursive(
     sources: Vec<Box<dyn source::Source>>,
     args: args::ViewerArgs,
 ) -> anyhow::Result<cursive::Cursive> {
-    let mut cursive = cursive::default();
+    let mut cursive =
+        cursive::Cursive::try_new(create_backend).context("Could not create Cursive instance")?;
 
     cursive.set_user_data(Context::new(sources, args)?);