compiler: implement recover() built-in function

testdata/recover.go

@@ -0,0 +1,99 @@
+package main
+
+func main() {
+	println("# simple recover")
+	recoverSimple()
+
+	println("\n# recover with result")
+	result := recoverWithResult()
+	println("result:", result)
+
+	println("\n# nested defer frame")
+	nestedDefer()
+
+	println("\n# nested panic: panic inside recover")
+	nestedPanic()
+
+	println("\n# panic inside defer")
+	panicInsideDefer()
+
+	println("\n# panic replace")
+	panicReplace()
+}
+
+func recoverSimple() {
+	defer func() {
+		println("recovering...")
+		printitf("recovered:", recover())
+	}()
+	println("running panic...")
+	panic("panic")
+}
+
+func recoverWithResult() (result int) {
+	defer func() {
+		printitf("recovered:", recover())
+	}()
+	result = 3
+	println("running panic...")
+	panic("panic")
+}
+
+func nestedDefer() {
+	defer func() {
+		printitf("recovered:", recover())
+	}()
+
+	func() {
+		// The defer here doesn't catch the panic using recover(), so the outer
+		// panic should do that.
+		defer func() {
+			println("deferred nested function")
+		}()
+		panic("panic")
+	}()
+	println("unreachable")
+}
+
+func nestedPanic() {
+	defer func() {
+		printitf("recovered 1:", recover())
+
+		defer func() {
+			printitf("recovered 2:", recover())
+		}()
+
+		panic("foo")
+	}()
+	panic("panic")
+}
+
+func panicInsideDefer() {
+	defer func() {
+		printitf("recovered:", recover())
+	}()
+	defer func() {
+		panic("panic")
+	}()
+}
+
+func panicReplace() {
+	defer func() {
+		printitf("recovered:", recover())
+	}()
+	defer func() {
+		println("panic 2")
+		panic("panic 2")
+	}()
+	println("panic 1")
+	panic("panic 1")
+}
+
+func printitf(msg string, itf interface{}) {
+	switch itf := itf.(type) {
+	case string:
+		println(msg, itf)
+	default:
+		println(msg, itf)
+	}
+}