{"record":{"id":"9e3fcd5b67a887f7","repo":"wasmerio/wasmer","slug":"unsupported-backend-type","errorCode":null,"errorMessage":"Unsupported backend type","messagePattern":"Unsupported backend type","errorType":"exception","errorClass":"anyhow::Error","httpStatus":null,"severity":"error","filePath":"lib/cli/src/backend.rs","lineNumber":723,"sourceCode":"                    match p {\n                        Profiler::Perfmap => config.enable_perfmap(),\n                        Profiler::Gdb => config.enable_debugger(Debugger::Gdb),\n                        Profiler::Lldb => config.enable_debugger(Debugger::Lldb),\n                    }\n                }\n\n                let engine = wasmer_compiler::EngineBuilder::new(config)\n                    .set_features(Some(supported_features))\n                    .set_target(Some(target.clone()))\n                    .engine()\n                    .into();\n                Ok(engine)\n            }\n            #[cfg(feature = \"v8\")]\n            Self::V8 => Ok(wasmer::v8::V8::new().into()),\n            Self::Headless => bail!(\"Headless is not a valid runtime to instantiate directly\"),\n            #[allow(unreachable_patterns)]\n            _ => bail!(\"Unsupported backend type\"),\n        }\n    }\n\n    /// Check if this backend supports all the required WebAssembly features\n    #[allow(unreachable_code)]\n    pub fn supports_features(&self, required_features: &Features, target: &Target) -> bool {\n        // Map BackendType to the corresponding wasmer::BackendKind\n        let backend_kind = match self {\n            #[cfg(feature = \"singlepass\")]\n            Self::Singlepass => wasmer::BackendKind::Singlepass,\n            #[cfg(feature = \"cranelift\")]\n            Self::Cranelift => wasmer::BackendKind::Cranelift,\n            #[cfg(feature = \"llvm\")]\n            Self::LLVM => wasmer::BackendKind::LLVM,\n            #[cfg(feature = \"v8\")]\n            Self::V8 => wasmer::BackendKind::V8,\n            Self::Headless => return false, // Headless can't compile\n            #[allow(unreachable_patterns)]","sourceCodeStart":705,"sourceCodeEnd":741,"githubUrl":"https://github.com/wasmerio/wasmer/blob/8c4b9ee9d33fb2068863fbb3d328683e7e6ff7f5/lib/cli/src/backend.rs#L705-L741","documentation":"get_engine matches only the backend variants compiled into the current feature set (sys backends plus the v8 feature). Any other Backend value falls into the catch-all arm and bails with 'Unsupported backend type'. This occurs when a backend was compiled out of the binary via cargo feature flags or an unknown variant is constructed.","triggerScenarios":"Calling get_engine() on a Backend variant not enabled at compile time (e.g. requesting V8 without the 'v8' feature, or a backend like LLVM when built without it), or any exotic/unrecognized Backend value.","commonSituations":"Running a wasmer binary that was built without the needed feature flags; CLI --engine flag referencing a backend the build does not include; version drift where a backend name no longer exists.","solutions":["Rebuild wasmer with the required feature enabled (e.g. cargo build --features v8, or enable cranelift/llvm/singlepass features).","Pick a backend that the installed binary supports (run `wasmer config` / check available engines).","If a script passes a backend name, correct the typo or stale name."],"exampleFix":"// before (binary built without v8)\nlet engine = Backend::V8.get_engine()?; // Unsupported backend type\n// after: rebuild\n// cargo build --release --features v8\nlet engine = Backend::V8.get_engine()?;","handlingStrategy":"fallback","validationCode":"fn backend_supported(b: &Backend, features: &Features) -> bool {\n    b.supports_features(features, &Target::default())\n}","typeGuard":"fn is_compiled_in(b: &Backend) -> bool {\n    matches!(b, Backend::Cranelift | Backend::LLVM | Backend::Singlepass) || cfg!(feature = \"v8\") && matches!(b, Backend::V8)\n}","tryCatchPattern":"match backend.get_engine() {\n    Ok(e) => e,\n    Err(e) if e.to_string() == \"Unsupported backend type\" => {\n        eprintln!(\"backend {:?} unavailable in this build; falling back to cranelift\", backend);\n        Backend::Cranelift.get_engine()?\n    }\n    Err(e) => return Err(e),\n}","preventionTips":["Check supports_features/available engines before selecting a backend at runtime.","Enable the matching cargo feature (v8, llvm, singlepass) for the backend you deploy.","Pin wasmer builds so feature sets match the environments that run your commands."],"tags":["wasmer","backend","feature-flags","compile-time"],"backgroundTag":"unsupported-backend-type","analyzedSha":"8c4b9ee9d33fb2068863fbb3d328683e7e6ff7f5","analyzedAt":"2026-09-01T23:06:31.009Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-09T06:17:21.866Z"}