x/tools: support for embedded fields in struct literals

[adonovan]

#9859 added language and compiler support for T{f: ...} where T is a struct type and f is an embedded field. This issue tracks the work of auditing x/tools and ensuring that it too supports this feature.

Gopls

• Completion (@adonovan)
• Fill Struct (@h9jiang)
• Hover
• Definition
• Diagnostics

If you find more cases to consider, please report as comments so we can track.

These are the only other places I found in my audit of x/tools (adonovan):

• go/analysis/passes/composite analyzer (https://go.dev/cl/773222)
• gopls compositeLiteralFields inlay hints should reveal the implicit selectors T{k: v} => T{a.b.k: v} (https://go.dev/cl/782060)
• internal/refactor/inliner analyzeAssignment contains 2 suspect uses of KeyValueExpr (audited, both benign --adonovan)

Modernizer

• Issue cmd/fix, x/tools/gopls: modernizer for direct references to embedded fields in struct literals #77965 tracks investigation/implementation for the need of modernizer for this.

Other Tools (to be notified)

• staticcheck (go1.27: support generic methods, and embedded field selectors in struct literals dominikh/go-tools#1718)
• golangcli-lint (go1.27: support generic methods golangci/golangci-lint#6603)
• dlv (go1.27: support generic methods go-delve/delve#4360)

[gabyhelp]

Related Issues

• spec: direct reference to embedded fields in struct literals #9859 (closed)
• x/tools/gopls: modernizer for direct references to embedded fields in struct literals #77965

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[gopherbot]

Change https://go.dev/cl/763220 mentions this issue: gopls: add test cases for embedded fields in struct literals

[gopherbot]

Change https://go.dev/cl/763920 mentions this issue: go/ssa: support direct references to embedded fields in struct lit

[h9jiang]

Comment for assignment.

[h9jiang]

For case like FillStruct analyzer, we have a case where a embedded struct is partially filled:

type E2 struct {
	C int
}

type E1 struct {
	A int
	B int
	E2
}

type T struct {
	E1

	Other E1
}

normally, if the struct is completely empty, we would fill in

_ = T{} // before

_ = T{ // after
	E1:    E1{},
	Other: E1{},
}

however, if the struct is partially filled, I think we should still offer user to fill in the struct and we will follow their practice and keep B & E2 promoted. Follow rule:

if field x is promoted and filled, we will promote all the other fields at the same level of x.

_ = T{ // after
	A: 1,
	Other: E1{},
}

_ = T{ // after
	A: 1,
	B: 1, // promoted
	E2: E2{}, // promoted
	Other: E1{},
}

My thought of why we still want to offer such code action when it's partially filled:

User used to have the option to first fill in T then, use the same code action to fill in Other: E1 and E1: E1. but because it is promoted, we no longer have a struct lit for user to trigger such code action to fill the field E1: E1.

Leave a thumb up for approval, leave a comment for rejection or ideas.

[gopherbot]

Change https://go.dev/cl/765620 mentions this issue: gopls/internal/analysis/fillstruct: support promoted field detection

[gopherbot]

Change https://go.dev/cl/766240 mentions this issue: gopls/internal/analysis/fillstruct: do not offer if contains untagged

[gopherbot]

Change https://go.dev/cl/766280 mentions this issue: gopls/internal/analysis/fillstruct: support embedded fields