internal/lsp: add text edits for unkeyed literals

Add text edits that a user can accept to make the unkeyed composite
literals keyed from the inlay hints. The text edits modify all of
the unkeyed fields in a composite literal, since a mixture of keyed
and unkeyed fields are not allowed.

Change-Id: I0683fbaa5e22bc004b91c98fc09e495e797826ee
Reviewed-on: https://go-review.googlesource.com/c/tools/+/414855
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Suzy Mueller <suzmue@golang.org>

internal/lsp/source/inlay_hint.go

@@ -344,7 +344,7 @@ func compositeLiteralFields(node ast.Node, tmap *lsppos.TokenMapper, info *types
 	}
 
 	var hints []protocol.InlayHint
-
+	var allEdits []protocol.TextEdit
 	for i, v := range compLit.Elts {
 		if _, ok := v.(*ast.KeyValueExpr); !ok {
 			start, ok := tmap.Position(v.Pos())
@@ -360,8 +360,17 @@ func compositeLiteralFields(node ast.Node, tmap *lsppos.TokenMapper, info *types
 				Kind:         protocol.Parameter,
 				PaddingRight: true,
 			})
+			allEdits = append(allEdits, protocol.TextEdit{
+				Range:   protocol.Range{Start: start, End: start},
+				NewText: strct.Field(i).Name() + ": ",
+			})
 		}
 	}
+	// It is not allowed to have a mix of keyed and unkeyed fields, so
+	// have the text edits add keys to all fields.
+	for i := range hints {
+		hints[i].TextEdits = allEdits
+	}
 	return hints
 }