gopls/internal/golang: add type inlayhint for variable decl

Skip type inlayhint if the type is explicitly written like:

var foo string

to avoid duplicated information.

Rename gomod inlayhint.go to inlay_hint.go for consistency.

For golang/go#73946

Change-Id: I94944d2fde685ee0b57ce9fdb38cee31bb1038b2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/677935
Auto-Submit: Hongxiang Jiang <hxjiang@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: h9jiang

gopls/internal/golang/inlay_hint.go

@@ -165,13 +165,33 @@ func funcTypeParams(info *types.Info, pgf *parsego.File, qual types.Qualifier, c
 }
 
 func assignVariableTypes(info *types.Info, pgf *parsego.File, qual types.Qualifier, cur inspector.Cursor, add func(protocol.InlayHint)) {
-	for curAssign := range cur.Preorder((*ast.AssignStmt)(nil)) {
-		stmt := curAssign.Node().(*ast.AssignStmt)
-		if stmt.Tok != token.DEFINE {
-			continue
-		}
-		for _, v := range stmt.Lhs {
-			variableType(info, pgf, qual, v, add)
+	for node := range cur.Preorder((*ast.AssignStmt)(nil), (*ast.ValueSpec)(nil)) {
+		switch n := node.Node().(type) {
+		case *ast.AssignStmt:
+			if n.Tok != token.DEFINE {
+				continue
+			}
+			for _, v := range n.Lhs {
+				variableType(info, pgf, qual, v, add)
+			}
+		case *ast.GenDecl:
+			if n.Tok != token.VAR {
+				continue
+			}
+			for _, v := range n.Specs {
+				spec := v.(*ast.ValueSpec)
+				// The type of the variable is written, skip showing type of this var.
+				// ```go
+				// var foo string
+				// ```
+				if spec.Type != nil {
+					continue
+				}
+
+				for _, v := range spec.Names {
+					variableType(info, pgf, qual, v, add)
+				}
+			}
 		}
 	}
 }

gopls/internal/mod/inlayhint.go gopls/internal/mod/inlay_hint.gogopls/internal/mod/inlayhint.go renamed to gopls/internal/mod/inlay_hint.go

@@ -363,6 +363,8 @@ func SumNumbers[K comparable, V Number](m map[K]V) V {
 package inlayHint //@inlayhints(vartypes)
 
 func assignTypes() {
+	var x string
+	var y = ""
 	i, j := 0, len([]string{})-1
 	println(i, j)
 }
@@ -385,6 +387,8 @@ func compositeLitType() {
 package inlayHint //@inlayhints(vartypes)
 
 func assignTypes() {
+	var x string
+	var y = ""
 	i< int>, j< int> := 0, len([]string{})-1
 	println(i, j)
 }

gopls/internal/test/marker/testdata/inlayhints/inlayhints.txt

@@ -25,11 +25,11 @@ go 1.21.9
 //@inlayhints(out)
 package p
 
-var _ = rand.Float64() 
+var _ = rand.Float64()
 
 -- @out --
 //@inlayhints(out)
 package p
 
-var _ = rand.Float64() 
+var _ = rand.Float64()