Accept nil ctx in NewRuntime (#752)

Signed-off-by: Anuraag Agrawal <anuraaga@gmail.com>

runtime.go

@@ -127,6 +127,9 @@ func NewRuntime(ctx context.Context) Runtime {
 
 // NewRuntimeWithConfig returns a runtime with the given configuration.
 func NewRuntimeWithConfig(ctx context.Context, rConfig RuntimeConfig) Runtime {
+	if ctx == nil {
+		ctx = context.Background()
+	}
 	if v := ctx.Value(version.WazeroVersionKey{}); v == nil {
 		ctx = context.WithValue(ctx, version.WazeroVersionKey{}, wazeroVersion)
 	}

runtime_test.go

@@ -22,6 +22,23 @@ var (
 )
 
 func TestNewRuntimeWithConfig_version(t *testing.T) {
+	// Make sure nil ctx doesn't panic
+	tests := []struct {
+		name string
+		ctx  context.Context
+	}{
+		{
+			name: "not nil",
+			ctx:  testCtx,
+		},
+		{
+			name: "nil",
+			ctx:  nil,
+		},
+	}
+	for _, tc := range tests {
+		tt := tc
+		t.Run(tt.name, func(t *testing.T) {
 			cfg := NewRuntimeConfig().(*runtimeConfig)
 			oldNewEngine := cfg.newEngine
 			cfg.newEngine = func(ctx context.Context, features wasm.Features) wasm.Engine {
@@ -31,7 +48,9 @@ func TestNewRuntimeWithConfig_version(t *testing.T) {
 				require.Equal(t, wazeroVersion, v.(string))
 				return oldNewEngine(ctx, features)
 			}
-	_ = NewRuntimeWithConfig(testCtx, cfg)
+			_ = NewRuntimeWithConfig(tt.ctx, cfg)
+		})
+	}
 }
 
 func TestRuntime_CompileModule(t *testing.T) {