chore: add missing tests for var-declarations, fix any/interface{} ty…

…pe issue (#1154)

* chore: add missing tests for var-declarations, fix any/interface{} type issue

rule/var_declarations.go

@@ -85,7 +85,7 @@ func (w *lintVarDeclarations) Visit(node ast.Node) ast.Visitor {
 		// If the RHS is a isZero value, suggest dropping it.
 		isZero := false
 		if lit, ok := rhs.(*ast.BasicLit); ok {
-			isZero = zeroLiteral[lit.Value]
+			isZero = isZeroValue(lit.Value, v.Type)
 		} else if isIdent(rhs, "nil") {
 			isZero = true
 		}
@@ -142,3 +142,16 @@ func validType(t types.Type) bool {
 		t != types.Typ[types.Invalid] &&
 		!strings.Contains(t.String(), "invalid type") // good but not foolproof
 }
+
+func isZeroValue(litValue string, typ ast.Expr) bool {
+	switch val := typ.(type) {
+	case *ast.Ident:
+		if val.Name == "any" {
+			return litValue == "nil"
+		}
+	case *ast.InterfaceType:
+		return litValue == "nil"
+	}
+
+	return zeroLiteral[litValue]
+}

testdata/golint/var_declaration.go

@@ -84,3 +84,9 @@ var y string = q(1).String() // MATCH /should omit type string from declaration
 type q int
 
 func (q) String() string { return "I'm a q" }
+
+// The only true zero value for any/interface{} is nil. Others will be considered non-zero.
+var z1 any = 0           // No warning, zero value for any is nil
+var z2 any = nil         // MATCH /should drop = nil from declaration of var z2; it is the zero value/
+var z3 interface{} = 0   // No warning, zero value for any is nil
+var z4 interface{} = nil // MATCH /should drop = nil from declaration of var z4; it is the zero value/