Don't try to parse MSRV if feature is not enabled

src/cargo/util/toml/mod.rs

@@ -1058,7 +1058,7 @@ impl TomlManifest {
             Edition::Edition2015
         };
 
-        if let Some(rust_version) = &project.rust_version {
+        let rust_version = if let Some(rust_version) = &project.rust_version {
             if features.require(Feature::rust_version()).is_err() {
                 let mut msg =
                     "`rust-version` is not supported on this version of Cargo and will be ignored"
@@ -1077,28 +1077,31 @@ impl TomlManifest {
                     );
                 }
                 warnings.push(msg);
-            }
-
-            let req = match semver::VersionReq::parse(rust_version) {
-                // Exclude semver operators like `^` and pre-release identifiers
-                Ok(req) if rust_version.chars().all(|c| c.is_ascii_digit() || c == '.') => req,
-                _ => bail!("`rust-version` must be a value like \"1.32\""),
-            };
-
-            if let Some(first_version) = edition.first_version() {
-                let unsupported =
-                    semver::Version::new(first_version.major, first_version.minor - 1, 9999);
-                if req.matches(&unsupported) {
-                    bail!(
-                        "rust-version {} is older than first version ({}) required by \
-                         the specified edition ({})",
-                        rust_version,
-                        first_version,
-                        edition,
-                    )
+                None
+            } else {
+                let req = match semver::VersionReq::parse(rust_version) {
+                    // Exclude semver operators like `^` and pre-release identifiers
+                    Ok(req) if rust_version.chars().all(|c| c.is_ascii_digit() || c == '.') => req,
+                    _ => bail!("`rust-version` must be a value like \"1.32\""),
+                };
+                if let Some(first_version) = edition.first_version() {
+                    let unsupported =
+                        semver::Version::new(first_version.major, first_version.minor - 1, 9999);
+                    if req.matches(&unsupported) {
+                        bail!(
+                            "rust-version {} is older than first version ({}) required by \
+                                the specified edition ({})",
+                            rust_version,
+                            first_version,
+                            edition,
+                        )
+                    }
                 }
+                Some(rust_version.clone())
             }
-        }
+        } else {
+            None
+        };
 
         if project.metabuild.is_some() {
             features.require(Feature::metabuild())?;
@@ -1339,7 +1342,7 @@ impl TomlManifest {
             workspace_config,
             features,
             edition,
-            project.rust_version.clone(),
+            rust_version,
             project.im_a_teapot,
             project.default_run.clone(),
             Rc::clone(me),

tests/testsuite/rust_version.rs

@@ -11,7 +11,7 @@ fn rust_version_gated() {
                 [package]
                 name = "foo"
                 version = "0.0.1"
-                rust-version = "1.17"
+                rust-version = "1.9999"
             "#,
         )
         .file("src/lib.rs", "")
@@ -31,7 +31,7 @@ fn rust_version_gated() {
                 [package]
                 name = "foo"
                 version = "0.0.1"
-                rust-version = "1.17"
+                rust-version = "1.9999"
             "#,
         )
         .file("src/lib.rs", "")