Fix #122: don't crash govet on tests-only packages

Author: jirfag

Diff for: .travis.yml

@@ -7,6 +7,7 @@ script: make check_generated test
 
 after_success:
   - test -n "$TRAVIS_TAG" && docker login -u="$DOCKER_USERNAME" -p="$DOCKER_PASSWORD"
+  - echo "travis go version='$TRAVIS_GO_VERSION'"
 
 # needed for the docker pipe
 services:
@@ -18,4 +19,4 @@ deploy:
   script: curl -sL https://git.io/goreleaser | bash
   on:
     tags: true
-    condition: $TRAVIS_GO_VERSION =~ ^1\.10\.[0-9]+$
+    condition: $TRAVIS_GO_VERSION =~ ^1\.10\.

Diff for: pkg/golinters/govet.go

@@ -76,6 +76,9 @@ func (g Govet) runOnInstalledPackages(ctx context.Context, lintCtx *linter.Conte
 			astFiles = append(astFiles, af.F)
 			fset = af.Fset
 		}
+		if len(astFiles) == 0 {
+			continue
+		}
 		issues, err := govetAPI.Analyze(astFiles, fset, nil,
 			lintCtx.Settings().Govet.CheckShadowing)
 		if err != nil {
@@ -216,6 +219,9 @@ func (g Govet) runOnSourcePackages(ctx context.Context, lintCtx *linter.Context)
 	// TODO: check .S asm files: govet can do it if pass dirs
 	var govetIssues []govetAPI.Issue
 	for _, pkg := range lintCtx.Program.InitialPackages() {
+		if len(pkg.Files) == 0 {
+			continue
+		}
 		issues, err := govetAPI.Analyze(pkg.Files, lintCtx.Program.Fset, pkg,
 			lintCtx.Settings().Govet.CheckShadowing)
 		if err != nil {