False negative with defer

[maratori]

The same issue exists in gostaticanalysis/nilerr#19.

The following test fails:

func TestFails() error {
	defer func() {}() // the test passes if you remove defer
	err := func() error { return nil }()
	if err != nil {
		return err
	}
	err2 := func() error { return nil }()
	if err2 != nil {
		return err // want `return a nil value error after check error`
	}
	return nil
}

[alingse]

 🤔 I will check it 🤔

[alingse]

I use another function and print the blocks and instrs

func Call18() error {
	defer func() {}() // the test passes if you remove defer

	err := Do()
	if err != nil {
		return err
	}
	err2 := Do2()
	if err2 != nil {
		return err // want `return a nil value error after check error`
	}
	return nil
}

blocks[0].Instrs[0]     *ssa.Alloc      local error ()
blocks[0].Instrs[1]     *ssa.Defer      defer Call18$1()
blocks[0].Instrs[2]     *ssa.Call       Do()
blocks[0].Instrs[3]     *ssa.BinOp      t1 != nil:error
blocks[0].Instrs[4]     *ssa.If if t2 goto 2 else 3

blocks[1].Instrs[0]     *ssa.UnOp       *t0
blocks[1].Instrs[1]     *ssa.Return     return t3

blocks[2].Instrs[0]     *ssa.Store      *t0 = t1
blocks[2].Instrs[1]     *ssa.RunDefers  rundefers
blocks[2].Instrs[2]     *ssa.UnOp       *t0
blocks[2].Instrs[3]     *ssa.Return     return t4

blocks[3].Instrs[0]     *ssa.Call       Do2()
blocks[3].Instrs[1]     *ssa.BinOp      t5 != nil:error
blocks[3].Instrs[2]     *ssa.If if t6 goto 4 else 5

blocks[4].Instrs[0]     *ssa.Store      *t0 = t1
blocks[4].Instrs[1]     *ssa.RunDefers  rundefers
blocks[4].Instrs[2]     *ssa.UnOp       *t0
blocks[4].Instrs[3]     *ssa.Return     return t7

blocks[5].Instrs[0]     *ssa.Store      *t0 = nil:error
blocks[5].Instrs[1]     *ssa.RunDefers  rundefers
blocks[5].Instrs[2]     *ssa.UnOp       *t0
blocks[5].Instrs[3]     *ssa.Return     return t8

the return err was convert to *ssa.Store *t0 = nil:error a store instr, this is not support by nilness, I will try to support it if I can.