gradle/gradle · error · BrokenResultException

Could not determine %s metadata: %s produced unexpected outp

Error message

Could not determine %s metadata: %s produced unexpected output.

What it means

SwiftcMetadataProvider runs `swiftc --version` and scans stdout for a line containing 'Swift version', parsing the version from token index 2 ('Swift version 4.0.2 (...)') or index 3 when the line starts with 'Apple' ('Apple Swift version 4.0.2 (...)'). If no line matches, BrokenResultException 'Could not determine SwiftC metadata: <binary> produced unexpected output' is thrown.

Source

Thrown at platforms/native/platform-native/src/main/java/org/gradle/nativeplatform/toolchain/internal/swift/metadata/SwiftcMetadataProvider.java:78

    @Override
    protected SwiftcMetadata parseCompilerOutput(String stdout, String stderr, File swiftc, List<File> path) {
        BufferedReader reader = new BufferedReader(new StringReader(stdout));
        try {
            String line;
            while ((line = reader.readLine()) != null) {
                if (line.contains("Swift version")) {
                    String[] tokens = line.split(" ");
                    // Assuming format: 'Swift version 4.0.2 (...)'
                    int i = 2;
                    if ("Apple".equals(tokens[0])) {
                        // Actual format: 'Apple Swift version 4.0.2 (...)'
                        i++;
                    }
                    VersionNumber version = VersionNumber.parse(tokens[i]);
                    return new DefaultSwiftcMetadata(line, version);
                }
            }
            throw new BrokenResultException(String.format("Could not determine %s metadata: %s produced unexpected output.", getCompilerType().getDescription(), swiftc.getName()));
        } catch (IOException e) {
            // Should not happen when reading from a StringReader
            throw UncheckedException.throwAsUncheckedException(e);
        }
    }

    private static class DefaultSwiftcMetadata implements SwiftcMetadata {
        private final String versionString;
        private final VersionNumber version;

        DefaultSwiftcMetadata(String versionString, VersionNumber version) {
            this.versionString = versionString;
            this.version = version;
        }

        @Override
        public String getVendor() {
            return versionString;

View on GitHub (pinned to 534f27719b)

Solutions

Run `swiftc --version` yourself and check a line contains 'Swift version <n.n.n>'; if it reads 'Swift compiler version ...', switch to a release toolchain (banner 'Swift version ...').
Point the Swift toolchain configuration at the real swiftc binary, not a wrapper.
Upgrade Gradle - newer metadata providers parse development-snapshot banners too.

Example fix

# before
$ swiftc --version
Swift compiler version 6.0 (swift-6.0-DEVELOPMENT)   # no 'Swift version' line -> error
# after: install/use a release toolchain
$ swiftc --version
Swift version 5.10 (swift-5.10-RELEASE)
Target: x86_64-unknown-linux-gnu

Defensive patterns

Strategy: validation

Validate before calling

def out = 'swiftc --version'.execute().in.text
if (!out.readLines().any { it.contains('Swift version') }) {
    throw new GradleException('swiftc --version has no "Swift version" line (dev snapshot or wrapper?); install a release toolchain')
}

Prevention

Use release Swift toolchains with Gradle; development snapshots print 'Swift compiler version' banners this parser rejects.
Point the Swift toolchain path at the real swiftc, not a wrapper script.
Add a CI preflight running swiftc --version and asserting the banner format.

When it happens

Trigger: A swiftc whose --version banner does not contain the literal substring 'Swift version': development snapshots print 'Swift compiler version 6.0-dev ...' (the word 'compiler' breaks the match); non-Apple custom builds with a different banner; tokens[2]/tokens[3] not being a parseable version; empty stdout when the binary is a broken shim.

Common situations: Using a swift.org DEVELOPMENT/main-snapshot toolchain (banner 'Swift compiler version ...') with an older Gradle; aliasing swiftc to a wrapper that swallows stdout; Swift toolchains from unusual vendors on CI.

Related errors

AI-assisted analysis of gradle/gradle@534f27719b (2026-08-22). Data as JSON: /api/errors/501749411bfbf565. Report an issue: GitHub.