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proposal: encoding/xml: Unmarshal comment with tag #39357

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LinWanCen opened this issue Jun 2, 2020 · 6 comments
Closed

proposal: encoding/xml: Unmarshal comment with tag #39357

LinWanCen opened this issue Jun 2, 2020 · 6 comments
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@LinWanCen
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What did you do?

<mapper namespace="TEST">

  <!-- Multi-table -->
  <select id="MULTI" parameterType="java.util.Map" resultType="Map">
    SELECT * FROM information_schema.COLUMNS, COLUMNS, ${schema}.TABLES
  </select>

  <!-- Join -->
  <select id="JOIN" parameterType="java.util.Map" resultType="Map">
    SELECT * FROM information_schema.COLUMNS JOIN TABLES
  </select>
<mapper namespace="TEST">
type (
	Mapper struct {
		XMLName   xml.Name
		Namespace string `xml:"namespace,attr"`
		Select    []sql  `xml:"select"`
		Insert    []sql  `xml:"insert"`
		Update    []sql  `xml:"update"`
		Delete    []sql  `xml:"delete"`
	}

	sql struct {
		Comment string `xml:",comment"`
		Id      string `xml:"id,attr"`
		SQL     string `xml:",innerxml"`
	}
)

func test(path string)  {
	model := Mapper{}
	xml.Unmarshal(util.ReadByte(path), &model)
}

What did you expect to see?

Mapper.Select[0].Comment == "Multi-table"
Mapper.Select[1].Comment == "Join"

if

	Mapper struct {
		XMLName   xml.Name
		Namespace string `xml:"namespace,attr"`
		Comment []string `xml:"select,comment"`
		Select    []sql  `xml:"select"`
		Insert    []sql  `xml:"insert"`
		Update    []sql  `xml:"update"`
		Delete    []sql  `xml:"delete"`
	}

then

Mapper.Comment[0] == "Multi-table"
Mapper.Comment[1] == "Join"

What did you see instead?

Mapper.Select[0].Comment == ""
Mapper.Select[1].Comment == ""

if

	Mapper struct {
		XMLName   xml.Name
		Namespace string `xml:"namespace,attr"`
		Comment string `xml:",comment"`
		Select    []sql  `xml:"select"`
		Insert    []sql  `xml:"insert"`
		Update    []sql  `xml:"update"`
		Delete    []sql  `xml:"delete"`
	}

then

Mapper.Comment  == "Multi-table Join"
@gopherbot gopherbot added this to the Proposal milestone Jun 2, 2020
@rsc rsc added this to Incoming in Proposals (old) Jun 10, 2020
@rsc
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rsc commented Jul 14, 2021

I understand this request to be asking for a way to collect comment text in XML unmarshaling, same as the ability to collect inner CDATA text. That's interesting but I am not sure whether we should go down that road. If there is any data structure to unmarshal in the XML, it seems like it should be in non-comment form.

It would be especially problematic to have to attach comments to the XML elements that follow them, as in the example (<!-- Multi-table --> and <!-- Join --> are in the same overall XML element but are being attached to sibling elements instead of the parent!). I don't think this is tenable for encoding/xml to take on.

Note that using xml.Token it is possible to read the data stream and do whatever you like. If you know that there is a stream of comment/object/comment/object/... then you can use an xml.Decoder to use Decode.Token to get the comment, then Decoder.Decode to get the object, and repeat.

@rsc rsc changed the title Proposal: encoding/xml Unmarshal comment with tag proposal: encoding/xml: Unmarshal comment with tag Jul 14, 2021
@rsc rsc moved this from Incoming to Active in Proposals (old) Jul 14, 2021
@rsc
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rsc commented Jul 14, 2021

This proposal has been added to the active column of the proposals project
and will now be reviewed at the weekly proposal review meetings.
— rsc for the proposal review group

@rsc rsc mentioned this issue Jul 14, 2021
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@rsc
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rsc commented Jul 21, 2021

Based on the discussion above, this proposal seems like a likely decline.
— rsc for the proposal review group

@rsc rsc moved this from Active to Likely Decline in Proposals (old) Jul 21, 2021
@LinWanCen
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LinWanCen commented Jul 21, 2021 •
edited

There may not be other languages ​​that support parsing comments. Golang is the only one I know, but connecting comments together is not very practical.

Developers can do it through complex coding, but this is a bit difficult for ordinary people.

I think this way of parsing is similar to parsing documentation comments on functions, which is very elegant and practical.

@LinWanCen
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LinWanCen commented Jul 21, 2021 •
edited

如果在 XML 中有任何要解组的数据结构，它似乎应该是非注释形式。

This is indeed the case. My demand actually comes from parsing the stock code written by others in a large project. They use this kind of annotation method to describe the service configuration. I need to find all the services and bring an annotation explanation. I started I didn't have time to study how to write it. In order to realize it quickly, regular expressions were used at the time, but it was quite complicated😄.
I very much hope that this problem can be solved simply and without bugs.

@rsc rsc moved this from Likely Decline to Declined in Proposals (old) Jul 28, 2021
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rsc commented Jul 28, 2021

No change in consensus, so declined.
— rsc for the proposal review group

@rsc rsc closed this as completed Jul 28, 2021
@golang golang locked and limited conversation to collaborators Jul 28, 2022
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