hclwrite: add read and write API for ObjectConsExpr

[bbasata]

Description

Rewrite object values.

config := []byte(`a = {
    hat = "derby", (cat) = "calico" }` + "\n")

bowler := hclwrite.TokensForValue(cty.StringVal(`bowler`))

file, _ := ParseConfig(config, "<inline>", hcl.Pos{})
attr := file.Body().GetAttribute("a")

expr := attr.Expr().AsObjectConsExpr()
key, value := expr.SetItemRaw("hat", bowler)

fmt.Printf("key: ")
key.BuildTokens(nil).WriteTo(os.Stdout)
fmt.Println()
fmt.Println("value: ")
value.BuildTokens(nil).WriteTo(os.Stdout)
fmt.Println()

Related Issue

#810

[bbasata]

Rebased onto 2994071. The new commits belonging to this PR are b5b53ef and 321afff.

[bbasata]

Rebased onto 2994071. The new commits belonging to this PR are b5b53ef and 321afff.

@mildwonkey: I'm marking this one for review, with no expectation that it's quite ready to merge yet. It's simply the next one in the sequence that we're collaborating on.

I've exercised this in a client application to a high degree of confidence. Now, to turn "the change that works" into "the right change."

[bbasata]

@mildwonkey: I'm marking this one for review, with no expectation that it's quite ready to merge yet. It's simply the next one in the sequence that we're collaborating on.

ℹ️ This new test will see some changes in its tree. This is a consequence of parsing the object-construct item key as an expression, so it now has a richer sub-tree.

TestParse/a_=_{___hat_=_{__style_=_"derby",__color_=_(variable)___},___cat_=_"calico"_}