Blocks do not have proper return types in if-statements

[AndreasHassing]

In the following program (Fibonacci):

int fib(int n) {
  if (n == 0) {
    return 0;
  } else if (n == 1) {
    return 1;
  } else {
    return fib(n-1) + fib(n-2);
  }
}

void start() {
  print fib(14);
}

The compiled WASM-module won't run in browsers, due to the fact that the generated IF statement states that a I32 value must be returned, but the inner block does not define a return type.

Compiled WASM-module translated to WAST:

(module
  (type (;0;) (func (param i32)))
  (type (;1;) (func (param i32)))
  (type (;2;) (func (param i32) (result i32)))
  (type (;3;) (func))
  (import "imports" "printi" (func (;0;) (type 0)))
  (import "imports" "printc" (func (;1;) (type 1)))
  (func (;2;) (type 2) (param i32) (result i32)
    get_local 0
    i32.const 0
    i32.eq
    if i32  ;; label = @1
      block  ;; label = @2 ;; this block should also return an i32!
        i32.const 0
        return
      end
    else
      get_local 0
      i32.const 1
      i32.eq
      if i32  ;; label = @2
        block  ;; label = @3 ;; this block should also return an i32!
          i32.const 1
          return
        end
      else
        block  ;; label = @3 ;; this block should also return an i32!
          get_local 0
          i32.const 1
          i32.sub
          call 2
          get_local 0
          i32.const 2
          i32.sub
          call 2
          i32.add
          return
        end
      end
    end)
  (func (;3;) (type 3)
    i32.const 14
    call 2
    call 0)
  (memory (;0;) 1)
  (start 3))

Error generated by wast2wasm:

test.wast:15:9: type stack size too small at if true branch. got 0, expected at least 1
        return
        ^^^^^^
test.wast:24:11: type stack size too small at if true branch. got 0, expected at least 1
          return
          ^^^^^^
test.wast:37:11: type stack size too small at if false branch. got 0, expected at least 1
          return
          ^^^^^^