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text/template/parse: Unexpected Behaviour of ActionNode.Position in text/template - Potential Bug? #66423

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shallowclouds opened this issue Mar 20, 2024 · 7 comments
Closed

text/template/parse: Unexpected Behaviour of ActionNode.Position in text/template - Potential Bug? #66423

shallowclouds opened this issue Mar 20, 2024 · 7 comments
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NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one.

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@shallowclouds
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Go version

go version go1.21.4 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE='on'
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/xxx/Library/Caches/go-build'
GOENV='/Users/xxx/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/xxx/projects/gopath/pkg/mod'
GOOS='darwin'
GOPATH='/Users/xxx/projects/gopath'
GOROOT='/opt/homebrew/opt/go/libexec'
GOSUMDB='sum.golang.google.cn'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/opt/homebrew/opt/go/libexec/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.21.4'
GCCGO='gccgo'
AR='ar'
CC='cc'
CXX='c++'
CGO_ENABLED='1'
GOMOD='/Users/xxx/projects/xxx/go.mod'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/mt/w_9vxxsn0ssfxz46n8lbrykh0000gp/T/go-build2022525700=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

https://go.dev/play/p/U8UabjbhJsN

// You can edit this code!
// Click here and start typing.
package main

import (
	"fmt"
	"reflect"
	"text/template"
)

func main() {
	temp := `{{.locale}}`
	tree, err := template.New("test").Parse(temp)
	if err != nil {
		panic(err)
	}

	node := tree.Root.Nodes[0]
	fmt.Println(reflect.TypeOf(node))
	// expect: {{.locale}} 0
	fmt.Println(node.String(), node.Position())
	// expect: {{.locale}}
	fmt.Println(temp[node.Position():])
}

What did you see happen?

I am currently developing a highlighter for text/template scripts. To accomplish this, I require an Abstract Syntax Tree (AST) for the provided template. During this process, I encountered an unexpected behaviour with the Position method of the ActionNode.

Contrary to my expectations, the Position of the ActionNode does not include the delimiter ('{{'). However, the String method does return the full {{.locale}}, inclusive of the delimiter. This discrepancy has prompted me to question whether there is a bug, or if I have misunderstood the purpose of the Position function in the Action interface.

According to the given documentation comment, Position() Pos should represent the 'byte position of the start of node in full original input string'. This, in my understanding, should include the delimiter.

Could you please clarify this discrepancy, or confirm if this is indeed a bug? Thank you for your time and assistance.

What did you expect to see?

temp := `{{.locale}}`
tree, err := template.New("test").Parse(temp)
if err != nil {
  panic(err)
}

node := tree.Root.Nodes[0]
fmt.Println(reflect.TypeOf(node))
// expect: {{.locale}} 0
fmt.Println(node.String(), node.Position())
// expect: {{.locale}}
fmt.Println(temp[node.Position():])
@dr2chase
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@robpike, @mvdan, can you give this a look?

@dr2chase dr2chase added the NeedsInvestigation Someone must examine and confirm this is a valid issue and not a duplicate of an existing one. label Mar 20, 2024
@robpike
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robpike commented Mar 20, 2024

The action starts inside the delimiter, so the position field is correct. The String method includes the delimiter for ease of use. So yes, they are inconsistent and perhaps should be consistent, but it's more likely to break things than improve them to try to change this. Plus, you'd need to decide what change to make.

I think it can stay as is.

@shallowclouds
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The action starts inside the delimiter, so the position field is correct. The String method includes the delimiter for ease of use. So yes, they are inconsistent and perhaps should be consistent, but it's more likely to break things than improve them to try to change this. Plus, you'd need to decide what change to make.

I think it can stay as is.

Thanks for replying, I understanded. May I ask why the position does not contains "{{ if" and other things, without these, it is nearly impossible to map nodes range to the original text for highlighter, and is not like other common ast parsers.

@robpike
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robpike commented Mar 20, 2024

As I said, the action starts inside the delimiter, that's why.

@shallowclouds
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shallowclouds commented Mar 21, 2024 •
edited

As I said, the action starts inside the delimiter, that's why.

Sorry I may not have made it clear, I mean if there should be a node wraps the action node but contains the delimiter and prefix such as "if" and "range" to make the AST nodes ranges cover all the original text.

@robpike
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robpike commented Mar 21, 2024

It's impractical to change the parse tree given the compatibility promise. You'll just have to code around it, which shouldn't be too inconvenient.

@shallowclouds
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It's impractical to change the parse tree given the compatibility promise. You'll just have to code around it, which shouldn't be too inconvenient.

Got it, thanks.

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@dr2chase @robpike @shallowclouds