1 files changed, 59 insertions, 0 deletions
diff --git a/compiler/rustc_macros/src/current_version.rs b/compiler/rustc_macros/src/current_version.rs
new file mode 100644
index 000000000..5e3b91c17
--- /dev/null
+++ b/compiler/rustc_macros/src/current_version.rs
@@ -0,0 +1,59 @@
+use proc_macro::TokenStream;
+use proc_macro2::Span;
+use quote::quote;
+use syn::parse::{Parse, ParseStream};
+use syn::{parenthesized, parse_macro_input, LitStr, Token};
+
+pub struct Input {
+    variable: LitStr,
+}
+
+mod kw {
+    syn::custom_keyword!(env);
+}
+
+impl Parse for Input {
+    // Input syntax is `env!("CFG_RELEASE")` to facilitate grepping.
+    fn parse(input: ParseStream<'_>) -> syn::Result<Self> {
+        let paren;
+        input.parse::<kw::env>()?;
+        input.parse::<Token![!]>()?;
+        parenthesized!(paren in input);
+        let variable: LitStr = paren.parse()?;
+        Ok(Input { variable })
+    }
+}
+
+pub(crate) fn current_version(input: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(input as Input);
+
+    TokenStream::from(match RustcVersion::parse_env_var(&input.variable) {
+        Ok(RustcVersion { major, minor, patch }) => quote!(
+            Self { major: #major, minor: #minor, patch: #patch }
+        ),
+        Err(err) => syn::Error::new(Span::call_site(), err).into_compile_error(),
+    })
+}
+
+struct RustcVersion {
+    major: u16,
+    minor: u16,
+    patch: u16,
+}
+
+impl RustcVersion {
+    fn parse_env_var(env_var: &LitStr) -> Result<Self, Box<dyn std::error::Error>> {
+        let value = proc_macro::tracked_env::var(env_var.value())?;
+        Self::parse_str(&value)
+            .ok_or_else(|| format!("failed to parse rustc version: {:?}", value).into())
+    }
+
+    fn parse_str(value: &str) -> Option<Self> {
+        // Ignore any suffixes such as "-dev" or "-nightly".
+        let mut components = value.split('-').next().unwrap().splitn(3, '.');
+        let major = components.next()?.parse().ok()?;
+        let minor = components.next()?.parse().ok()?;
+        let patch = components.next().unwrap_or("0").parse().ok()?;
+        Some(RustcVersion { major, minor, patch })
+    }
+}