internal/lsp: suppress parameter hint when argument matches parameter

Suppress the parameter hint when it would present redundant
information.

Fixes golang/go#2361

Change-Id: I4340a903046f212f8a035eab847da665e2692f1a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/419497
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Suzy Mueller <suzmue@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>

internal/lsp/source/inlay_hint.go

@@ -154,17 +154,24 @@ func parameterNames(node ast.Node, tmap *lsppos.TokenMapper, info *types.Info, _
 		if i > params.Len()-1 {
 			break
 		}
-		value := params.At(i).Name()
+		param := params.At(i)
 		// param.Name is empty for built-ins like append
-		if value == "" {
+		if param.Name() == "" {
 			continue
 		}
+		// Skip the parameter name hint if the arg matches the
+		// the parameter name.
+		if i, ok := v.(*ast.Ident); ok && i.Name == param.Name() {
+			continue
+		}
+
+		label := param.Name()
 		if signature.Variadic() && i == params.Len()-1 {
-			value = value + "..."
+			label = label + "..."
 		}
 		hints = append(hints, protocol.InlayHint{
 			Position:     &start,
-			Label:        buildLabel(value + ":"),
+			Label:        buildLabel(label + ":"),
 			Kind:         protocol.Parameter,
 			PaddingRight: true,
 		})

internal/lsp/testdata/inlay_hint/parameter_names.go

@@ -42,4 +42,9 @@ func foobar() {
 	kipp("a", "b", "c")
 	plex("a", "b", "c")
 	tars("a", "b", "c")
+	foo, bar, baz := "a", "b", "c"
+	kipp(foo, bar, baz)
+	plex("a", bar, baz)
+	tars(foo+foo, (bar), "c")
+
 }

internal/lsp/testdata/inlay_hint/parameter_names.go.golden

@@ -43,5 +43,10 @@ func foobar() {
 	kipp(<foo: >"a", <bar: >"b", <baz: >"c")
 	plex(<foo: >"a", <bar: >"b", <baz: >"c")
 	tars(<foo: >"a", <bar: >"b", <baz: >"c")
+	foo< string>, bar< string>, baz< string> := "a", "b", "c"
+	kipp(foo, bar, baz)
+	plex(<foo: >"a", bar, baz)
+	tars(<foo: >foo+foo, <bar: >(bar), <baz: >"c")
+
 }