Add ability to take glob patterns from stdin

as requested in issue solidiquis#51

This adds a new (hidden) flag `--stdin` to indicate that `et` should
take input from stdin. Since the naming convention is to use `-` for
this, we replace the args `-` with `--stdin` before we hand them over
to Clap.

Example usage:
```shell
$ touch hello.rs helLo.rs HELlo.rs
$  fd -e rs '^hel[lL]o' | et -
           erdtree
     0   B ├─ hello.rs
     0   B └─ helLo.rs
```

src/main.rs

@@ -20,7 +20,10 @@
 )]
 use clap::CommandFactory;
 use render::{context::Context, tree::Tree};
-use std::{io::stdout, process::ExitCode};
+use std::{
+    io::{stdout, BufRead},
+    process::ExitCode,
+};
 
 /// Filesystem operations.
 mod fs;
@@ -44,7 +47,17 @@ fn main() -> ExitCode {
 }
 
 fn run() -> Result<(), Box<dyn std::error::Error>> {
-    let ctx = Context::init()?;
+    let mut ctx = Context::init()?;
+
+    if ctx.stdin {
+        let mut stdin_lines = std::io::stdin()
+            .lock()
+            .lines()
+            .filter_map(|s| s.ok())
+            .filter(|l| !l.is_empty())
+            .collect::<Vec<String>>();
+        ctx.glob.append(&mut stdin_lines);
+    }
 
     if let Some(shell) = ctx.completions {
         clap_complete::generate(shell, &mut Context::command(), "et", &mut stdout().lock());

src/render/context/mod.rs

@@ -39,7 +39,7 @@ pub struct Context {
 
     /// Include or exclude files using glob patterns
     #[arg(short, long)]
-    glob: Vec<String>,
+    pub glob: Vec<String>,
 
     /// Include or exclude files using glob patterns; case insensitive
     #[arg(long)]
@@ -128,13 +128,22 @@ pub struct Context {
     /// Don't read configuration file
     #[arg(long)]
     pub no_config: bool,
+
+    /// Take input from Stdin
+    #[arg(long, hide = true)]
+    pub stdin: bool,
 }
 
 impl Context {
     /// Initializes [Context], optionally reading in the configuration file to override defaults.
     /// Arguments provided will take precedence over config.
     pub fn init() -> Result<Self, Error> {
-        let user_args = Self::command().args_override_self(true).get_matches();
+        let mut args: Vec<_> = std::env::args().collect();
+        crate::utils::detect_stdin(&mut args);
+
+        let user_args = Self::command()
+            .args_override_self(true)
+            .get_matches_from(args);
 
         let no_config = user_args.get_one("no_config").map_or(false, bool::clone);
 

src/utils.rs

@@ -25,3 +25,21 @@ where
         .filter(|item| set.insert(item.to_owned()))
         .collect::<Vec<T>>()
 }
+
+/// Follow the naming convention and use "-" to specify a Standard Input.
+/// Retain "-" from [`args`] and add "--stdin" if necessary.
+pub fn detect_stdin(args: &mut Vec<String>) {
+    let dash = String::from("-");
+    let stdin_flag = String::from("--stdin");
+
+    let mut is_stdin = false;
+    args.retain(|e| {
+        if *e == dash {
+            is_stdin = true
+        };
+        *e != dash
+    });
+    if is_stdin && !args.contains(&stdin_flag) {
+        args.push(stdin_flag)
+    }
+}