hakari/cargo_toml.rs
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// Copyright (c) The cargo-guppy Contributors
// SPDX-License-Identifier: MIT OR Apache-2.0
use atomicwrites::{AtomicFile, OverwriteBehavior};
use camino::{Utf8Path, Utf8PathBuf};
use diffy::Patch;
use std::{error, fmt, io};
/// Support for maintaining `Cargo.toml` files that unify features in a workspace.
///
/// This struct maintains a context around a `Cargo.toml` file. It provides facilities for diffing
/// the contents of the file, and for writing out new contents.
///
/// # Structure of the Cargo.toml file
///
/// The `Cargo.toml` file is treated as partially generated. It is expected to have a section marked
/// off as, for example:
///
/// ```toml
/// [package]
/// ...
///
/// ### BEGIN HAKARI SECTION
/// [dependencies]
/// ...
///
/// [build-dependencies]
/// ...
///
/// [dev-dependencies]
/// ...
/// ### END HAKARI SECTION
/// ```
///
/// The part of the `Cargo.toml` file between the `BEGIN HAKARI SECTION` and `END HAKARI SECTION`
/// lines is managed by this struct, and changes to it may not be preserved. The part of the file
/// outside this section can be edited and its contents will be preserved.
///
/// # Setting up a new package
///
/// For Hakari to manage a package, a bit of initial prep work must be done:
///
/// 1. Add a new library package in a desired location within your workspace, for example: `cargo
/// new --lib hakari-package`.
/// 2. Copy and paste the following lines of code to the end of the package's `Cargo.toml` file. Be
/// sure to put in a trailing newline.
///
/// ```toml
/// ### BEGIN HAKARI SECTION
///
/// ### END HAKARI SECTION
///
/// ```
///
/// 3. Add an empty `build.rs` file (the exact contents don't matter, but the presence of this file
/// makes build dependencies work properly).
///
/// ```
/// fn main() {}
/// ```
#[derive(Clone, Debug)]
pub struct HakariCargoToml {
toml_path: Utf8PathBuf,
contents: String,
// Start and end offsets for the section to replace.
start_offset: usize,
end_offset: usize,
}
impl HakariCargoToml {
/// The string `"\n### BEGIN HAKARI SECTION\n"`. This string marks the beginning of the
/// generated section.
pub const BEGIN_SECTION: &'static str = "\n### BEGIN HAKARI SECTION\n";
/// The string `"\n### END HAKARI SECTION\n"`. This string marks the end of the generated
/// section.
pub const END_SECTION: &'static str = "\n### END HAKARI SECTION\n";
/// Creates a new instance of `HakariCargoToml` with the `Cargo.toml` located at the given path.
/// Reads the contents of the file off of disk.
///
/// If the path is relative, it is evaluated with respect to the current directory.
///
/// Returns an error if the file couldn't be read (other than if the file wasn't found, which
/// is a case handled by this struct).
pub fn new(toml_path: impl Into<Utf8PathBuf>) -> Result<Self, CargoTomlError> {
let toml_path = toml_path.into();
let contents = match std::fs::read_to_string(&toml_path) {
Ok(contents) => contents,
Err(error) => return Err(CargoTomlError::Io { toml_path, error }),
};
Self::new_in_memory(toml_path, contents)
}
/// Creates a new instance of `HakariCargoToml` at the given workspace root and crate
/// directory. Reads the contents of the file off of disk.
///
/// This is a convenience method around appending `crate_dir` and `Cargo.toml` to
/// `workspace_root`.
///
/// If the path is relative, it is evaluated with respect to the current directory.
pub fn new_relative(
workspace_root: impl Into<Utf8PathBuf>,
crate_dir: impl AsRef<Utf8Path>,
) -> Result<Self, CargoTomlError> {
let mut toml_path = workspace_root.into();
toml_path.push(crate_dir);
toml_path.push("Cargo.toml");
Self::new(toml_path)
}
/// Creates a new instance of `HakariCargoToml` with the given path with the given contents as
/// read from disk.
///
/// This may be useful for test scenarios.
pub fn new_in_memory(
toml_path: impl Into<Utf8PathBuf>,
contents: String,
) -> Result<Self, CargoTomlError> {
let toml_path = toml_path.into();
// Look for the start and end offsets.
let start_offset = match contents.find(Self::BEGIN_SECTION) {
Some(offset) => {
// Add the length of BEGIN_SECTION so that anything after that is replaced.
offset + Self::BEGIN_SECTION.len()
}
None => return Err(CargoTomlError::GeneratedSectionNotFound { toml_path }),
};
// Start searching from 1 before the end of the BEGIN text so that we find the END text
// even if there's nothing in between.
let end_offset = match contents[(start_offset - 1)..].find(Self::END_SECTION) {
Some(offset) => start_offset + offset,
None => return Err(CargoTomlError::GeneratedSectionNotFound { toml_path }),
};
Ok(Self {
toml_path,
contents,
start_offset,
end_offset,
})
}
/// Returns the toml path provided at construction time.
pub fn toml_path(&self) -> &Utf8Path {
&self.toml_path
}
/// Returns the contents of the file on disk as read at construction time.
pub fn contents(&self) -> &str {
&self.contents
}
/// Returns the start and end offsets of the part of the file treated as generated.
pub fn generated_offsets(&self) -> (usize, usize) {
(self.start_offset, self.end_offset)
}
/// Returns the part of the file that is treated as generated.
///
/// This part of the file will be replaced on write.
pub fn generated_contents(&self) -> &str {
&self.contents[self.start_offset..self.end_offset]
}
/// Returns true if the contents on disk are different from the provided TOML output.
pub fn is_changed(&self, toml: &str) -> bool {
self.generated_contents() != toml
}
/// Computes the diff between the contents on disk and the provided TOML output.
///
/// This returns a `diffy::Patch`, which can be formatted through methods provided by `diffy`.
/// `diffy` is re-exported at the top level of this crate.
///
/// # Examples
///
/// TODO
pub fn diff_toml<'a>(&'a self, toml: &'a str) -> Patch<'a, str> {
diffy::create_patch(self.generated_contents(), toml)
}
/// Writes out the provided TOML to the generated section of the file. The rest of the file is
/// left unmodified.
///
/// `self` is consumed because the contents of the file are now assumed to be invalid.
///
/// Returns true if the contents were different and the file was written out, false if the
/// contents were the same and the file was *not* written out, and an error if there was an
/// issue while writing the file out.
pub fn write_to_file(self, toml: &str) -> Result<bool, CargoTomlError> {
if !self.is_changed(toml) {
// Don't write out the file if it hasn't changed to avoid bumping mtimes.
return Ok(false);
}
let try_block = || {
let atomic_file = AtomicFile::new(&self.toml_path, OverwriteBehavior::AllowOverwrite);
atomic_file.write(|f| self.write(toml, f))
};
match (try_block)() {
Ok(()) => Ok(true),
Err(atomicwrites::Error::Internal(error)) | Err(atomicwrites::Error::User(error)) => {
Err(CargoTomlError::Io {
toml_path: self.toml_path,
error,
})
}
}
}
/// Writes out the full contents, including the provided TOML, to the given writer.
pub fn write(&self, toml: &str, mut out: impl io::Write) -> io::Result<()> {
write!(out, "{}", &self.contents[..self.start_offset])?;
write!(out, "{}", toml)?;
write!(out, "{}", &self.contents[self.end_offset..])
}
/// Writes out the full contents, including the provided TOML, to the given `fmt::Write`
/// instance.
///
/// `std::io::Write` expects bytes to be written to it, so using it with a `&mut String` is
/// inconvenient. This alternative is more convenient, and also works for `fmt::Formatter`
/// instances.
pub fn write_to_fmt(&self, toml: &str, mut out: impl fmt::Write) -> fmt::Result {
// No alternative to copy-pasting :(
write!(out, "{}", &self.contents[..self.start_offset])?;
write!(out, "{}", toml)?;
write!(out, "{}", &self.contents[self.end_offset..])
}
}
/// An error that can occur while reading or writing a `Cargo.toml` file.
#[derive(Debug)]
#[non_exhaustive]
pub enum CargoTomlError {
/// The contents of the `Cargo.toml` file could not be read or written.
Io {
/// The path that was attempted to be read.
toml_path: Utf8PathBuf,
/// The error that occurred.
error: io::Error,
},
/// The `Cargo.toml` was successfully read but `### BEGIN HAKARI SECTION` and
/// `### END HAKARI SECTION` couldn't be found.
GeneratedSectionNotFound {
/// The path that was read.
toml_path: Utf8PathBuf,
},
}
impl fmt::Display for CargoTomlError {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
match self {
CargoTomlError::Io { toml_path, .. } => {
write!(f, "error while reading path '{}'", toml_path)
}
CargoTomlError::GeneratedSectionNotFound { toml_path, .. } => {
write!(
f,
"in '{}', unable to find\n\
### BEGIN HAKARI SECTION\n\
...\n\
### END HAKARI SECTION",
toml_path
)
}
}
}
}
impl error::Error for CargoTomlError {
fn source(&self) -> Option<&(dyn error::Error + 'static)> {
match self {
CargoTomlError::Io { error, .. } => Some(error),
CargoTomlError::GeneratedSectionNotFound { .. } => None,
}
}
}