staticcheck: don't crash when checking dot-imported constants in bitwise ops

Closes gh-719

(cherry picked from commit f5dad99)

Author: dominikh

staticcheck/lint.go

@@ -2711,6 +2711,10 @@ func CheckSillyBitwiseOps(pass *analysis.Pass) (interface{}, error) {
 			if !ok {
 				return
 			}
+			if obj.Pkg() != pass.Pkg {
+				// identifier was dot-imported
+				return
+			}
 			if v, _ := constant.Int64Val(obj.Val()); v != 0 {
 				return
 			}

staticcheck/lint_test.go

@@ -55,7 +55,7 @@ func TestAll(t *testing.T) {
 		"SA4013": {{Dir: "CheckDoubleNegation"}},
 		"SA4014": {{Dir: "CheckRepeatedIfElse"}},
 		"SA4015": {{Dir: "CheckMathInt"}},
-		"SA4016": {{Dir: "CheckSillyBitwiseOps"}, {Dir: "CheckSillyBitwiseOps_shadowedIota"}},
+		"SA4016": {{Dir: "CheckSillyBitwiseOps"}, {Dir: "CheckSillyBitwiseOps_shadowedIota"}, {Dir: "CheckSillyBitwiseOps_dotImport"}},
 		"SA4017": {{Dir: "CheckPureFunctions"}},
 		"SA4018": {{Dir: "CheckSelfAssignment"}},
 		"SA4019": {{Dir: "CheckDuplicateBuildConstraints"}},

staticcheck/testdata/src/CheckSillyBitwiseOps_dotImport/foo.go

@@ -0,0 +1,3 @@
+package foo
+
+const X = 0

staticcheck/testdata/src/CheckSillyBitwiseOps_dotImport/foo_test.go

@@ -0,0 +1,5 @@
+package foo_test
+
+import . "CheckSillyBitwiseOps_dotImport"
+
+var _ = 1 | X