Replace version_check with our own parser to generate better errors

Cargo.toml

@@ -23,7 +23,4 @@ members = ["test_suite"]
 [lib]
 proc-macro = true
 
-[build-dependencies]
-version_check = "0.9.2"
-
 [dependencies]

README.md

@@ -59,7 +59,7 @@ pub const fn feature() {
 
 ## Alternatives
 
-This crate is proc-macro, but is very lightweight, depending only on [`version_check`](https://github.com/SergioBenitez/version_check) to determine the compiler version.
+This crate is proc-macro, but is very lightweight, and has no dependencies.
 
 You can manually define declarative macros with similar functionality (see [`if_rust_version`](https://github.com/ogoffart/if_rust_version#examples)), or [you can define the same function twice with different cfg](https://github.com/crossbeam-rs/crossbeam/blob/0b6ea5f69fde8768c1cfac0d3601e0b4325d7997/crossbeam-epoch/src/atomic.rs#L340-L372). (Note: the former approach requires more macros to be defined depending on the number of version requirements, the latter approach requires more functions to be maintained manually)
 

build.rs

@@ -1,14 +1,20 @@
-use std::{env, fs, path::PathBuf};
+use std::{
+    env, fs,
+    path::{Path, PathBuf},
+    process::Command,
+    str,
+};
 
 // The rustc-cfg strings below are *not* public API. Please let us know by
 // opening a GitHub issue if your build environment requires some way to enable
 // these cfgs other than by executing our build script.
 fn main() {
     println!("cargo:rustc-cfg=const_fn_has_build_script");
 
-    let version = match Version::new() {
-        Some(version) => format!("{:#?}\n", version),
-        None => panic!("unexpected output from `rustc --version`"),
+    let rustc = env::var_os("RUSTC").map_or_else(|| "rustc".into(), PathBuf::from);
+    let version = match Version::from_rustc(&rustc) {
+        Ok(version) => format!("{:#?}\n", version),
+        Err(e) => panic!("{}", e),
     };
 
     let out_dir = env::var_os("OUT_DIR").map(PathBuf::from).expect("OUT_DIR not set");
@@ -23,11 +29,50 @@ struct Version {
     nightly: bool,
 }
 
+// Based on https://github.com/cuviper/autocfg/blob/1.0.1/src/version.rs
+//
+// Using our own parser instead of the existing crates to generate better errors.
 impl Version {
-    fn new() -> Option<Self> {
-        let (version, channel, _date) = version_check::triple()?;
-        let (_major, minor, patch) = version.to_mmp();
-        let nightly = channel.is_nightly() || channel.is_dev();
+    // from the verbose version output
+    fn from_vv(vv: &str) -> Option<Self> {
+        // Find the release line in the verbose version output.
+        let release = vv
+            .lines()
+            .find(|line| line.starts_with("release: "))
+            .map(|line| &line["release: ".len()..])?;
+
+        // Split the version and channel info.
+        let mut version_channel = release.split('-');
+        let version = version_channel.next().unwrap();
+        let channel = version_channel.next();
+
+        // Split the version into semver components.
+        let mut digits = version.splitn(3, '.');
+        let major = digits.next()?;
+        if major != "1" {
+            return None;
+        }
+        let minor = digits.next()?.parse().ok()?;
+        let patch = digits.next().unwrap_or("0").parse().ok()?;
+
+        let nightly = channel.map_or(false, |c| c == "dev" || c == "nightly");
         Some(Version { minor, patch, nightly })
     }
+
+    fn from_rustc(rustc: &Path) -> Result<Self, String> {
+        let output =
+            Command::new(rustc).args(&["--version", "--verbose"]).output().map_err(|e| {
+                format!("failed to run `{} --version --verbose`: {}", rustc.display(), e)
+            })?;
+        if !output.status.success() {
+            return Err("could not execute rustc".to_string());
+        }
+        let output = str::from_utf8(&output.stdout).map_err(|e| {
+            format!("failed to parse output of `{} --version --verbose`: {}", rustc.display(), e)
+        })?;
+
+        Self::from_vv(output).ok_or_else(|| {
+            format!("unexpected output from `{} --version --verbose`: {}", rustc.display(), output)
+        })
+    }
 }

src/lib.rs

@@ -34,7 +34,7 @@
 //!
 //! # Alternatives
 //!
-//! This crate is proc-macro, but is very lightweight, depending only on [`version_check`](https://github.com/SergioBenitez/version_check) to determine the compiler version.
+//! This crate is proc-macro, but is very lightweight, and has no dependencies.
 //!
 //! You can manually define declarative macros with similar functionality (see [`if_rust_version`](https://github.com/ogoffart/if_rust_version#examples)), or [you can define the same function twice with different cfg](https://github.com/crossbeam-rs/crossbeam/blob/0b6ea5f69fde8768c1cfac0d3601e0b4325d7997/crossbeam-epoch/src/atomic.rs#L340-L372).
 //! (Note: the former approach requires more macros to be defined depending on the number of version requirements, the latter approach requires more functions to be maintained manually)