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add BuildChain, for associating two errors together #6

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add BuildChain, for associating two errors together #6

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cf1ae28
add BuildChain, for associating two errors together
gregwebs Sep 10, 2018
5847ae2
Merge remote-tracking branch 'main/master' into chain
gregwebs Sep 11, 2018
14e38e7
error chaining: add stack formatting
gregwebs Sep 11, 2018
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26 changes: 26 additions & 0 deletions errors.go
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Original file line number Diff line number Diff line change
Expand Up @@ -335,3 +335,29 @@ func Find(origErr error, test func(error) bool) error {
})
return foundErr
}

// Chain ties together two errors, giving them a Causer interface and a concatenated Error message.
type chain struct {
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@lysu lysu Sep 11, 2018 •
edited
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need override ErrorStack or %+v to print errors info before wrap recursively.

e.g.

func main() {
	_, err := time.ParseDuration("dfasdf")
	err = resetErrDataTooLong("c", 1,  err)
	err = resetErrDataTooLong("b", 2, err)
	fmt.Println(errors.ErrorStack(err))
}

func resetErrDataTooLong(colName string, rowIdx int, err error) error {
	newErr := types.ErrDataTooLong.Gen("Data too long for column '%v' at row %v", colName, rowIdx)
	return errors.Wrap(err, newErr)
}

should output:

time: invalid duration dfasdf
/home/robi/Code/go/src/github.com/pingcap/tidb/executor/test/zz.go:24: [types:1406]Data too long for column 'c' at row 1
/home/robi/Code/go/src/github.com/pingcap/tidb/executor/test/zz.go:24: [types:1406]Data too long for column 'b' at row 2

I think time: invalid duration dfasdf is what we need for this method

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Okay, the formatter is added.

currentErr error
prevErr error
}

func (err *chain) Error() string {
return err.currentErr.Error() + "\n" + err.prevErr.Error()
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Error should not got preErr.

e.g. TruncateErr, error info should only contain a column, b row value be truncate for end-user

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Okay, that makes sense since this is joining two separate errors. The previous will show up in the formatter.

}

func (err *chain) Cause() error {
return err.prevErr
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should we recursively find the root cause?

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No: this is the causer interface that goes just one level deeper.

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@lysu lysu Sep 11, 2018 •
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hi @gregwebs , I check juju's impl again. It seem will return .error in Cause(), and Error() will go preErr when error == nil...should we follow them ~?

expect this two question, others are look good to me

}

// BuildChain constructs a Chain.
// If the newer error is already a Chain, it will return the original ErrorChain
// modified so that the previous error is a chain.
func BuildChain(currentErr error, prevErr error) error {
if currentChain, ok := currentErr.(*chain); ok {
middleErr := currentChain.prevErr
currentChain.prevErr = &chain{middleErr, prevErr}
return currentChain
}
return &chain{currentErr, prevErr}
}
10 changes: 10 additions & 0 deletions errors_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -369,3 +369,13 @@ func TestWalkDeep(t *testing.T) {
t.Errorf("found not exists")
}
}

func TestChain(t *testing.T) {
if got := Cause(io.EOF).Error(); got != "EOF" {
t.Errorf("expected EOF, got %v", got)
}
caused := "caused"
if got := Cause(BuildChain(io.EOF, errors.New(caused))).Error(); got != caused {
t.Errorf("BuildChain expected caused")
}
}