gopls: skip unusedparams for generated files

The unusedparams analyzer makes a lot of noise for some generated files,
notably those generated by protoc-gen-go.
Since we can't actually edit generated files to fix this issue,
it seems better not to report it.

Fixes golang/go#71481

Change-Id: I4e73c74312dfea6ef4ce631cc029764519d6b809
Reviewed-on: https://go-review.googlesource.com/c/tools/+/645575
Reviewed-by: Sam Salisbury <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Robert Findley <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Reviewed-by: Hongxiang Jiang <[email protected]>

Author: samsalisbury

gopls/doc/analyzers.md

@@ -1000,6 +1000,8 @@ arguments at call sites, while taking care to preserve any side
 effects in the argument expressions; see
 https://github.com/golang/tools/releases/tag/gopls%2Fv0.14.
 
+This analyzer ignores generated code.
+
 Default: on.
 
 Package documentation: [unusedparams](https://pkg.go.dev/golang.org/x/tools/gopls/internal/analysis/unusedparams)

gopls/internal/analysis/unusedparams/doc.go

@@ -31,4 +31,6 @@
 // arguments at call sites, while taking care to preserve any side
 // effects in the argument expressions; see
 // https://github.com/golang/tools/releases/tag/gopls%2Fv0.14.
+//
+// This analyzer ignores generated code.
 package unusedparams

gopls/internal/analysis/unusedparams/testdata/src/generatedcode/generatedcode.go

@@ -0,0 +1,15 @@
+// Code generated with somegen DO NOT EDIT.
+//
+// Because this file is generated, there should be no diagnostics
+// reported for any unused parameters.
+
+package generatedcode
+
+// generatedInterface exists to ensure that the generated code
+// is considered when determining whether parameters are used
+// in non-generated code.
+type generatedInterface interface{ n(f bool) }
+
+func a(x bool) { println() }
+
+var v = func(x bool) { println() }

gopls/internal/analysis/unusedparams/testdata/src/generatedcode/generatedcode.go.golden

@@ -0,0 +1,20 @@
+package generatedcode
+
+// This file does not have the generated code comment.
+// It exists to ensure that generated code is considered
+// when determining whether or not function parameters
+// are used.
+
+type implementsGeneratedInterface struct{}
+
+// The f parameter should not be reported as unused,
+// because this method implements the parent interface defined
+// in the generated code.
+func (implementsGeneratedInterface) n(f bool) {
+	// The body must not be empty, otherwise unusedparams will
+	// not report the unused parameter regardles of the
+	// interface.
+	println()
+}
+
+func b(x bool) { println() } // want "unused parameter: x"

gopls/internal/analysis/unusedparams/testdata/src/generatedcode/nongeneratedcode.go

@@ -0,0 +1,20 @@
+package generatedcode
+
+// This file does not have the generated code comment.
+// It exists to ensure that generated code is considered
+// when determining whether or not function parameters
+// are used.
+
+type implementsGeneratedInterface struct{}
+
+// The f parameter should not be reported as unused,
+// because this method implements the parent interface defined
+// in the generated code.
+func (implementsGeneratedInterface) n(f bool) {
+	// The body must not be empty, otherwise unusedparams will
+	// not report the unused parameter regardles of the
+	// interface.
+	println()
+}
+
+func b(_ bool) { println() } // want "unused parameter: x"