Add fs utilities

Add dependency `remove_dir_all`
Note: On windows `std::fs::remove_dir_all` doesn't really work (rust-lang/rust#29497).

Cargo.toml

@@ -28,3 +28,4 @@ bindgen = "0.57"
 xmas-elf = "0.8"
 bitflags = "1.3"
 shlex = "1.0"
+remove_dir_all = "0.7"

src/fs.rs

@@ -0,0 +1,88 @@
+//! Filesystem utilities
+
+use std::fs::{self, File};
+use std::io::{self, Read, Seek};
+use std::path::Path;
+
+use anyhow::Result;
+
+pub use remove_dir_all::*;
+
+/// Copy `src_file` to `dest_file_or_dir` if `src_file` is different or the destination
+/// file doesn't exist.
+pub fn copy_file_if_different(
+    src_file: impl AsRef<Path>,
+    dest_file_or_dir: impl AsRef<Path>,
+) -> Result<()> {
+    let src_file: &Path = src_file.as_ref();
+    let dest_file_or_dir: &Path = dest_file_or_dir.as_ref();
+
+    assert!(src_file.is_file());
+
+    let mut src_fd = fs::File::open(src_file)?;
+
+    let (dest_fd, dest_file) = if dest_file_or_dir.exists() {
+        if dest_file_or_dir.is_dir() {
+            let dest_file = dest_file_or_dir.join(src_file.file_name().unwrap());
+            if dest_file.exists() {
+                (Some(fs::File::open(&dest_file)?), dest_file)
+            } else {
+                (None, dest_file)
+            }
+        } else {
+            (
+                Some(fs::File::open(dest_file_or_dir)?),
+                dest_file_or_dir.to_owned(),
+            )
+        }
+    } else {
+        (None, dest_file_or_dir.to_owned())
+    };
+
+    if let Some(mut dest_fd) = dest_fd {
+        if !is_file_eq(&mut src_fd, &mut dest_fd)? {
+            drop(dest_fd);
+            drop(src_fd);
+            fs::copy(src_file, dest_file)?;
+        }
+    } else {
+        fs::copy(src_file, dest_file)?;
+    }
+    Ok(())
+}
+
+/// Whether the file type and contents of `file` are equal to `other`.
+pub fn is_file_eq(file: &mut File, other: &mut File) -> Result<bool> {
+    let file_meta = file.metadata()?;
+    let other_meta = other.metadata()?;
+
+    if file_meta.file_type() == other_meta.file_type() && file_meta.len() == other_meta.len() {
+        let mut file_bytes = io::BufReader::new(&*file).bytes();
+        let mut other_bytes = io::BufReader::new(&*other).bytes();
+
+        // TODO: check performance
+        let result = loop {
+            match (file_bytes.next(), other_bytes.next()) {
+                (Some(Ok(b0)), Some(Ok(b1))) => {
+                    if b0 != b1 {
+                        break Ok(false);
+                    }
+                }
+                (None, None) => break Ok(true),
+                (None, Some(_)) | (Some(_), None) => break Ok(false),
+                (Some(Err(e)), _) | (_, Some(Err(e))) => return Err(e.into()),
+            }
+        };
+        drop(file_bytes);
+        drop(other_bytes);
+
+        // rewind files
+        // TODO: is this needed?
+        file.seek(io::SeekFrom::Start(0))?;
+        other.seek(io::SeekFrom::Start(0))?;
+
+        result
+    } else {
+        Ok(false)
+    }
+}

src/lib.rs

@@ -8,3 +8,4 @@ pub mod pio;
 pub mod python;
 pub mod symgen;
 pub mod utils;
+pub mod fs;