Extend the build directive syntax with cargo::metadata=

Author: 0xPoe

src/cargo/core/compiler/custom_build.rs

@@ -643,26 +643,97 @@ impl BuildOutput {
                 Ok(line) => line.trim(),
                 Err(..) => continue,
             };
-            let mut iter = line.splitn(2, ':');
+            let mut new_syntax = true;
+            let mut iter = line.splitn(2, "::");
             if iter.next() != Some("cargo") {
-                // skip this line since it doesn't start with "cargo:"
-                continue;
+                // For backwards compatibility, we also accept lines that start with "cargo:".
+                new_syntax = false;
+                iter = line.splitn(2, ":");
+                if iter.next() != Some("cargo") {
+                    // skip this line since it doesn't start with "cargo:" or "cargo::".
+                    continue;
+                }
             }
             let data = match iter.next() {
                 Some(val) => val,
                 None => continue,
             };
 
-            // getting the `key=value` part of the line
-            let mut iter = data.splitn(2, '=');
-            let key = iter.next();
-            let value = iter.next();
-            let (key, value) = match (key, value) {
-                (Some(a), Some(b)) => (a, b.trim_end()),
-                // Line started with `cargo:` but didn't match `key=value`.
+            // Old syntax:
+            //    cargo:rustc-flags=VALUE
+            //    cargo:KEY=VALUE (for other unreserved keys)
+            // New syntax:
+            //    cargo::rustc-flags=VALUE
+            //    cargo::metadata=KEY=VALUE (for other unreserved keys)
+            const RESERVED_KEYS: &[&str] = &[
+                "rustc-flags",
+                "rustc-link-lib",
+                "rustc-link-search",
+                "rustc-link-arg-cdylib",
+                "rustc-link-arg-bins",
+                "rustc-link-arg-bin",
+                "rustc-link-arg-tests",
+                "rustc-link-arg-benches",
+                "rustc-link-arg-examples",
+                "rustc-link-arg",
+                "rustc-cfg",
+                "rustc-check-cfg",
+                "rustc-env",
+                "warning",
+                "rerun-if-changed",
+                "rerun-if-env-changed",
+            ];
+            let mut iter = data.splitn(3, '=');
+            let part1 = iter.next();
+            let part2 = iter.next();
+            let part3 = iter.next();
+            let (key, value) = match (part1, part2, part3) {
+                (Some("metadata"), Some(a), Some(b)) => {
+                    // `cargo::metadata=` should only be used with the new syntax.
+                    if !new_syntax {
+                        bail!("invalid output in {}: `{}`\n\
+                            Expected a line with `cargo::metadata=KEY=VALUE`, but found `cargo:metadata=KEY=VALUE`.\n\
+                            See https://doc.rust-lang.org/cargo/reference/build-scripts.html#outputs-of-the-build-script \
+                            for more information about build script outputs.", whence, line,
+                        )
+                    }
+                    // Reserved keys should not be used with the `cargo::metadata` syntax.
+                    if new_syntax && RESERVED_KEYS.contains(&a) {
+                        bail!("invalid output in {}: `{}`\n\
+                            The reserved key `{}` cannot be used in a `cargo::metadata` line. Please use `cargo::{}=VAlUE` instead.\n\
+                            See https://doc.rust-lang.org/cargo/reference/build-scripts.html#outputs-of-the-build-script \
+                            for more information about build script outputs.", whence, line, a, a
+                        )
+                    }
+                    (a, b.trim_end().to_owned())
+                },
+                (Some(a), Some(b), None) => {
+                    // Only reserved keys should be used with the `cargo::` syntax.
+                    // Otherwise, it should be `cargo::metadata=KEY=VALUE`.
+                    if new_syntax && !RESERVED_KEYS.contains(&a) {
+                        bail!("invalid output in {}: `{}`\n\
+                            Expected a line with `cargo::metadata=KEY=VALUE` but it did not have the `metadata=` part.\n\
+                            See https://doc.rust-lang.org/cargo/reference/build-scripts.html#outputs-of-the-build-script \
+                            for more information about build script outputs.", whence, line
+                        )
+                    }
+                    (a, b.trim_end().to_owned())
+                },
+                (Some(a),Some(b),Some(c)) => {
+                    // Only reserved keys should be used with the `cargo::` syntax.
+                    // Otherwise, it should be `cargo::metadata=KEY=VALUE`.
+                    if new_syntax && !RESERVED_KEYS.contains(&a) {
+                        bail!("invalid output in {}: `{}`\n\
+                            Expected a line with `cargo::metadata=KEY=VALUE` but it did not have the `metadata=` part.\n\
+                            See https://doc.rust-lang.org/cargo/reference/build-scripts.html#outputs-of-the-build-script \
+                            for more information about build script outputs.", whence, line
+                        )
+                    }
+                    // For instance, `cargo:rustc-link-search=[KIND=]PATH` or `cargo::rustc-link-search=[KIND=]PATH`.
+                    (a, format!("{}={}", b, c).trim_end().to_owned())
+                }
+                // Line started with `cargo:` or `cargo::` but didn't match any of the above.
                 _ => bail!("invalid output in {}: `{}`\n\
-                    Expected a line with `cargo:key=value` with an `=` character, \
-                    but none was found.\n\
                     See https://doc.rust-lang.org/cargo/reference/build-scripts.html#outputs-of-the-build-script \
                     for more information about build script outputs.", whence, line),
             };