feat: inform users of breaking changes on first run (#619)

src/breaking_changes.rs

@@ -0,0 +1,156 @@
+//! Inform the users of the breaking changes introduced in this major release.
+//!
+//! Print the breaking changes and possibly a migration guide when:
+//!     1. The Topgrade being executed is a new major release
+//!     2. This is the first launch of that major release
+
+use crate::terminal::print_separator;
+#[cfg(windows)]
+use crate::WINDOWS_DIRS;
+#[cfg(unix)]
+use crate::XDG_DIRS;
+use color_eyre::eyre::Result;
+use etcetera::base_strategy::BaseStrategy;
+use std::{
+    fs::{read_to_string, OpenOptions},
+    io::Write,
+    path::PathBuf,
+    str::FromStr,
+};
+
+/// Version string x.y.z
+static VERSION_STR: &str = env!("CARGO_PKG_VERSION");
+
+/// Version info
+#[derive(Debug)]
+pub(crate) struct Version {
+    _major: u64,
+    minor: u64,
+    patch: u64,
+}
+
+impl FromStr for Version {
+    type Err = std::convert::Infallible;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        const NOT_SEMVER: &str = "Topgrade version is not semantic";
+        const NOT_NUMBER: &str = "Topgrade version is not dot-separated numbers";
+
+        let mut iter = s.split('.').take(3);
+        let major = iter.next().expect(NOT_SEMVER).parse().expect(NOT_NUMBER);
+        let minor = iter.next().expect(NOT_SEMVER).parse().expect(NOT_NUMBER);
+        let patch = iter.next().expect(NOT_SEMVER).parse().expect(NOT_NUMBER);
+
+        // They cannot be all 0s
+        assert!(
+            !(major == 0 && minor == 0 && patch == 0),
+            "Version numbers can not be all 0s"
+        );
+
+        Ok(Self {
+            _major: major,
+            minor,
+            patch,
+        })
+    }
+}
+
+impl Version {
+    /// True if this version is a new major release.
+    pub(crate) fn is_new_major_release(&self) -> bool {
+        // We have already checked that they cannot all be zeros, so `self.major`
+        // is guaranteed to be non-zero.
+        self.minor == 0 && self.patch == 0
+    }
+}
+
+/// Topgrade's breaking changes
+///
+/// We store them in the compiled binary.
+pub(crate) static BREAKINGCHANGES: &str = include_str!("../BREAKINGCHANGES.md");
+
+/// Return platform's data directory.
+fn data_dir() -> PathBuf {
+    #[cfg(unix)]
+    return XDG_DIRS.data_dir();
+
+    #[cfg(windows)]
+    return WINDOWS_DIRS.data_dir();
+}
+
+/// Return Topgrade's keep file path.
+///
+/// keep file is a file under the data directory containing a major version
+/// number, it will be created on first run and is used to check if an execution
+/// of Topgrade is the first run of a major release, for more details, see
+/// `first_run_of_major_release()`.
+fn keep_file_path() -> PathBuf {
+    let keep_file = "topgrade_keep";
+    data_dir().join(keep_file)
+}
+
+/// True if this is the first execution of a major release.
+pub(crate) fn first_run_of_major_release() -> Result<bool> {
+    let version = VERSION_STR.parse::<Version>().expect("should be a valid version");
+    let keep_file = keep_file_path();
+
+    // disable this lint here as the current code has better readability
+    #[allow(clippy::collapsible_if)]
+    if version.is_new_major_release() {
+        if !keep_file.exists() || read_to_string(&keep_file)? != VERSION_STR {
+            return Ok(true);
+        }
+    }
+
+    Ok(false)
+}
+
+/// Print breaking changes to the user.
+pub(crate) fn print_breaking_changes() {
+    let header = format!("Topgrade {VERSION_STR} Breaking Changes");
+    print_separator(header);
+    let contents = if BREAKINGCHANGES.is_empty() {
+        "No Breaking changes"
+    } else {
+        BREAKINGCHANGES
+    };
+    println!("{contents}\n");
+}
+
+/// This function will be ONLY executed when the user has confirmed the breaking
+/// changes, once confirmed, we write the keep file, which means the first run
+/// of this major release is finished.
+pub(crate) fn write_keep_file() -> Result<()> {
+    std::fs::create_dir_all(data_dir())?;
+    let keep_file = keep_file_path();
+
+    let mut file = OpenOptions::new()
+        .create(true)
+        .write(true)
+        .truncate(true)
+        .open(keep_file)?;
+    let _ = file.write(VERSION_STR.as_bytes())?;
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn is_new_major_release_works() {
+        let first_major_release: Version = "1.0.0".parse().unwrap();
+        let under_dev: Version = "0.1.0".parse().unwrap();
+
+        assert!(first_major_release.is_new_major_release());
+        assert!(!under_dev.is_new_major_release());
+    }
+
+    #[test]
+    #[should_panic(expected = "Version numbers can not be all 0s")]
+    fn invalid_version() {
+        let all_0 = "0.0.0";
+        all_0.parse::<Version>().unwrap();
+    }
+}