internal/lsp/source: add the unusedwrite analyzer

Fixes golang/go#44461

Change-Id: I0e002a26cd188cd9b5a14e44d7f880f9f414af36
Reviewed-on: https://go-review.googlesource.com/c/tools/+/295172
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Trust: Rebecca Stambler <rstambler@golang.org>
Trust: Peter Weinberger <pjw@google.com>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
diff --git a/internal/lsp/source/api_json.go b/internal/lsp/source/api_json.go
index 7352130..aa7b518 100755
--- a/internal/lsp/source/api_json.go
+++ b/internal/lsp/source/api_json.go
@@ -477,6 +477,11 @@
 							Default: "true",
 						},
 						{
+							Name:    "\"unusedwrite\"",
+							Doc:     "checks for unused writes\n\nThe analyzer reports instances of writes to struct fields and\narrays that are never read. Specifically, when a struct object\nor an array is copied, its elements are copied implicitly by\nthe compiler, and any element write to this copy does nothing\nwith the original object.\n\nFor example:\n\n\ttype T struct { x int }\n\tfunc f(input []T) {\n\t\tfor i, v := range input {  // v is a copy\n\t\t\tv.x = i  // unused write to field x\n\t\t}\n\t}\n\nAnother example is about non-pointer receiver:\n\n\ttype T struct { x int }\n\tfunc (t T) f() {  // t is a copy\n\t\tt.x = i  // unused write to field x\n\t}\n",
+							Default: "false",
+						},
+						{
 							Name:    "\"fillreturns\"",
 							Doc:     "suggested fixes for \"wrong number of return values (want %d, got %d)\"\n\nThis checker provides suggested fixes for type errors of the\ntype \"wrong number of return values (want %d, got %d)\". For example:\n\tfunc m() (int, string, *bool, error) {\n\t\treturn\n\t}\nwill turn into\n\tfunc m() (int, string, *bool, error) {\n\t\treturn 0, \"\", nil, nil\n\t}\n\nThis functionality is similar to https://github.com/sqs/goreturns.\n",
 							Default: "true",
@@ -990,6 +995,11 @@
 			Default: true,
 		},
 		{
+			Name:    "unusedwrite",
+			Doc:     "checks for unused writes\n\nThe analyzer reports instances of writes to struct fields and\narrays that are never read. Specifically, when a struct object\nor an array is copied, its elements are copied implicitly by\nthe compiler, and any element write to this copy does nothing\nwith the original object.\n\nFor example:\n\n\ttype T struct { x int }\n\tfunc f(input []T) {\n\t\tfor i, v := range input {  // v is a copy\n\t\t\tv.x = i  // unused write to field x\n\t\t}\n\t}\n\nAnother example is about non-pointer receiver:\n\n\ttype T struct { x int }\n\tfunc (t T) f() {  // t is a copy\n\t\tt.x = i  // unused write to field x\n\t}\n",
+			Default: false,
+		},
+		{
 			Name:    "fillreturns",
 			Doc:     "suggested fixes for \"wrong number of return values (want %d, got %d)\"\n\nThis checker provides suggested fixes for type errors of the\ntype \"wrong number of return values (want %d, got %d)\". For example:\n\tfunc m() (int, string, *bool, error) {\n\t\treturn\n\t}\nwill turn into\n\tfunc m() (int, string, *bool, error) {\n\t\treturn 0, \"\", nil, nil\n\t}\n\nThis functionality is similar to https://github.com/sqs/goreturns.\n",
 			Default: true,