Add methods to get/set the edition

src/lib.rs

@@ -91,6 +91,7 @@ pub struct AutoCfg {
     rustc_version: Version,
     target: Option<OsString>,
     no_std: bool,
+    edition: Option<String>,
     rustflags: Vec<String>,
     uuid: u64,
 }
@@ -203,6 +204,7 @@ impl AutoCfg {
             rustc_version: rustc_version,
             target: target,
             no_std: false,
+            edition: None,
             uuid: new_uuid(),
         };
 
@@ -246,6 +248,36 @@ impl AutoCfg {
         self.no_std = no_std;
     }
 
+    /// Returns the `--edition` string that is currently being passed to `rustc`, if any,
+    /// as configured by the [`set_edition`][Self::set_edition] method.
+    pub fn edition(&self) -> Option<&str> {
+        match self.edition {
+            Some(ref edition) => Some(&**edition),
+            None => None,
+        }
+    }
+
+    /// Sets the `--edition` string that will be passed to `rustc`,
+    /// or `None` to leave the compiler at its default edition.
+    ///
+    /// See also [The Rust Edition Guide](https://doc.rust-lang.org/edition-guide/).
+    ///
+    /// **Warning:** Setting an unsupported edition will likely cause **all** subsequent probes to
+    /// fail! As of this writing, the known editions and their minimum Rust versions are:
+    ///
+    /// | Edition | Version    |
+    /// | ------- | ---------- |
+    /// | 2015    | 1.27.0[^1] |
+    /// | 2018    | 1.31.0     |
+    /// | 2021    | 1.56.0     |
+    /// | 2024    | 1.85.0     |
+    ///
+    /// [^1]: Prior to 1.27.0, Rust was effectively 2015 Edition by default, but the concept hadn't
+    /// been established yet, so the explicit `--edition` flag wasn't supported either.
+    pub fn set_edition(&mut self, edition: Option<String>) {
+        self.edition = edition;
+    }
+
     /// Tests whether the current `rustc` reports a version greater than
     /// or equal to "`major`.`minor`".
     pub fn probe_rustc_version(&self, major: usize, minor: usize) -> bool {
@@ -282,6 +314,10 @@ impl AutoCfg {
             .arg(&self.out_dir)
             .arg("--emit=llvm-ir");
 
+        if let Some(edition) = self.edition.as_ref() {
+            command.arg("--edition").arg(edition);
+        }
+
         if let Some(target) = self.target.as_ref() {
             command.arg("--target").arg(target);
         }

tests/tests.rs

@@ -149,3 +149,41 @@ fn probe_cleanup() {
     // is empty -- i.e. the probe should have removed any output files.
     std::fs::remove_dir(&dir).unwrap();
 }
+
+#[test]
+fn editions() {
+    let mut ac = autocfg_for_test();
+    assert!(ac.edition().is_none());
+    assert!(ac.probe_raw("").is_ok());
+
+    for (edition, minor) in vec![(2015, 27), (2018, 31), (2021, 56), (2024, 85)] {
+        let edition = edition.to_string();
+        ac.set_edition(Some(edition.clone()));
+        assert_eq!(ac.edition(), Some(&*edition));
+        assert_min(&ac, 1, minor, ac.probe_raw("").is_ok());
+    }
+
+    ac.set_edition(Some("invalid".into()));
+    assert_eq!(ac.edition(), Some("invalid"));
+    assert!(ac.probe_raw("").is_err());
+
+    ac.set_edition(None);
+    assert!(ac.edition().is_none());
+    assert!(ac.probe_raw("").is_ok());
+}
+
+#[test]
+fn edition_keyword_try() {
+    let mut ac = autocfg_for_test();
+
+    if ac.probe_rustc_version(1, 27) {
+        ac.set_edition(Some(2015.to_string()));
+    }
+    assert!(ac.probe_expression("{ let try = 0; try }"));
+
+    if ac.probe_rustc_version(1, 31) {
+        ac.set_edition(Some(2018.to_string()));
+        assert!(!ac.probe_expression("{ let try = 0; try }"));
+        assert!(ac.probe_expression("{ let r#try = 0; r#try }"));
+    }
+}