fix: emit 1.77 syntax error only when msrv is incompatible

src/cargo/core/compiler/custom_build.rs

@@ -724,10 +724,9 @@ impl BuildOutput {
             pkg_descr: &str,
             msrv: &Option<RustVersion>,
         ) -> CargoResult<()> {
-            let new_syntax_added_in = &RustVersion::from_str("1.77.0")?;
-
             if let Some(msrv) = msrv {
-                if msrv < new_syntax_added_in {
+                let new_syntax_added_in = RustVersion::from_str("1.77.0")?;
+                if !new_syntax_added_in.is_compatible_with(msrv.as_partial()) {
                     bail!(
                         "the `cargo::` syntax for build script output instructions was added in \
                         Rust 1.77.0, but the minimum supported Rust version of `{pkg_descr}` is {msrv}.\n\

tests/testsuite/build_script.rs

@@ -5502,6 +5502,39 @@ for more information about build script outputs.
         .run();
 }
 
+#[cargo_test]
+fn test_new_syntax_with_compatible_partial_msrv() {
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+                [package]
+                name = "foo"
+                edition = "2015"
+                build = "build.rs"
+                rust-version = "1.77"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file(
+            "build.rs",
+            r#"
+                fn main() {
+                    println!("cargo::metadata=foo=bar");
+                }
+            "#,
+        )
+        .build();
+
+    p.cargo("check")
+        .with_stderr_contains(
+            "\
+[COMPILING] foo [..]
+",
+        )
+        .run();
+}
+
 #[cargo_test]
 fn test_old_syntax_with_old_msrv() {
     let p = project()