From 26727b84d92db09843175a945b93ad46ff7d0a53 Mon Sep 17 00:00:00 2001
From: =?utf8?q?Daniel=20Mart=C3=AD?= <mvdan@mvdan.cc>
Date: Mon, 11 Jun 2018 09:34:57 +0100
Subject: [PATCH] cmd/vet: simplify side effects func call logic
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Instead of first looking for values of unnamed signature type, first
treat the types and builtins. All the remaining cases will be what we're
after.

Change-Id: I328e22ae0be1cccaeb45ed4ddaa360233d447e7e
Reviewed-on: https://go-review.googlesource.com/117835
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Robert Griesemer <gri@golang.org>
---
 src/cmd/vet/bool.go | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/src/cmd/vet/bool.go b/src/cmd/vet/bool.go
index e8b73175aa..1cd477f988 100644
--- a/src/cmd/vet/bool.go
+++ b/src/cmd/vet/bool.go
@@ -9,7 +9,6 @@ package main
 import (
 	"go/ast"
 	"go/token"
-	"go/types"
 )
 
 func init() {
@@ -142,28 +141,22 @@ func hasSideEffects(f *File, e ast.Expr) bool {
 	ast.Inspect(e, func(node ast.Node) bool {
 		switch n := node.(type) {
 		case *ast.CallExpr:
-			// Don't call Type.Underlying(), since its lack
-			// lets us see the NamedFuncType(x) type
-			// conversion as a *types.Named.
 			typVal := f.pkg.types[n.Fun]
-			_, isSig := typVal.Type.(*types.Signature)
 			switch {
-			case typVal.IsValue() && isSig:
-				// If we have a value of unnamed signature type,
-				// this CallExpr is a non-builtin func call and
-				// not a type conversion. Conservatively assume
-				// that all function and method calls have side
-				// effects for now.
+			case typVal.IsType():
+				// Type conversion, which is safe.
+			case typVal.IsBuiltin():
+				// Builtin func, conservatively assumed to not
+				// be safe for now.
 				safe = false
 				return false
-			case typVal.IsBuiltin():
-				// For now, conservatively assume that all
-				// built-in functions have side effects.
+			default:
+				// A non-builtin func or method call.
+				// Conservatively assume that all of them have
+				// side effects for now.
 				safe = false
 				return false
 			}
-			// It's a type conversion, which cannot
-			// have side effects.
 		case *ast.UnaryExpr:
 			if n.Op == token.ARROW {
 				safe = false
-- 
2.50.0