Prevent finalize being called more than once per func/data (fixes #407)

cranelift/tests/moduletests.rs

@@ -1,9 +1,14 @@
 extern crate cranelift_codegen;
+extern crate cranelift_entity;
+extern crate cranelift_frontend;
 extern crate cranelift_module;
 extern crate cranelift_simplejit;
 
 use cranelift_codegen::ir::*;
 use cranelift_codegen::settings::*;
+use cranelift_codegen::Context;
+use cranelift_entity::EntityRef;
+use cranelift_frontend::*;
 use cranelift_module::*;
 use cranelift_simplejit::*;
 
@@ -25,3 +30,50 @@ fn error_on_incompatible_sig_in_declare_function() {
         .err()
         .unwrap(); // Make sure this is an error
 }
+
+fn define_simple_function(module: &mut Module<SimpleJITBackend>) -> FuncId {
+    let sig = Signature {
+        params: vec![],
+        returns: vec![],
+        call_conv: CallConv::SystemV,
+        argument_bytes: None,
+    };
+
+    let func_id = module
+        .declare_function("abc", Linkage::Local, &sig)
+        .unwrap();
+
+    let mut ctx = Context::new();
+    ctx.func = Function::with_name_signature(ExternalName::user(0, func_id.index() as u32), sig);
+    let mut func_ctx = FunctionBuilderContext::new();
+    {
+        let mut bcx: FunctionBuilder<Variable> = FunctionBuilder::new(&mut ctx.func, &mut func_ctx);
+        let ebb = bcx.create_ebb();
+        bcx.switch_to_block(ebb);
+        bcx.ins().return_(&[]);
+    }
+
+    module.define_function(func_id, &mut ctx).unwrap();
+
+    func_id
+}
+
+#[test]
+#[should_panic(expected = "function can't be finalized twice")]
+fn panic_on_double_finalize() {
+    let mut module: Module<SimpleJITBackend> = Module::new(SimpleJITBuilder::new());
+
+    let func_id = define_simple_function(&mut module);
+    module.finalize_function(func_id);
+    module.finalize_function(func_id);
+}
+
+#[test]
+#[should_panic(expected = "Result::unwrap()` on an `Err` value: DuplicateDefinition(\"abc\")")]
+fn panic_on_define_after_finalize() {
+    let mut module: Module<SimpleJITBackend> = Module::new(SimpleJITBuilder::new());
+
+    let func_id = define_simple_function(&mut module);
+    module.finalize_function(func_id);
+    define_simple_function(&mut module);
+}