Run multi-module check during presubmit

Makefile

@@ -6,6 +6,7 @@
 MYGOBIN := $(shell go env GOPATH)/bin
 SHELL := /bin/bash
 export PATH := $(MYGOBIN):$(PATH)
+MODULES := "cmd/config" "api/" "kustomize/" "kyaml/"
 
 .PHONY: all
 all: verify-kustomize
@@ -23,6 +24,7 @@ verify-kustomize: \
 .PHONY: prow-presubmit-check
 prow-presubmit-check: \
 	lint-kustomize \
+	test-multi-module \
 	test-unit-kustomize-all \
 	test-unit-cmd-all \
 	test-go-mod \
@@ -226,6 +228,17 @@ test-unit-cmd-all:
 test-go-mod:
 	./travis/check-go-mod.sh
 
+# Environment variables are defined at
+# https://github.com/kubernetes/test-infra/blob/master/prow/jobs.md#job-environment-variables
+.PHONY: test-multi-module
+test-multi-module:
+	go install github.com/google/go-github/github
+	go run ./cmd/prchecker \
+	-owner=$(REPO_OWNER) \
+	-repo=$(REPO_NAME) \
+	-pr=$(PR_NUM) \
+	$(MODULES)
+
 .PHONY:
 test-examples-e2e-kustomize: $(MYGOBIN)/mdrip $(MYGOBIN)/kind
 	( \

cmd/prchecker/main.go

@@ -27,9 +27,8 @@ import (
 
 // splitCommitsHelp is a help message displayed when a PR has commits which
 // span modules.
-const splitCommitsHelp = "\nModifications to multiple restricted directories occurred.\n" +
+const splitCommitsHelp = "\nCommits that include multiple Go modules must be split into multiple commits that each touch no more than one module.\n" +
-	"To resolve this please limit code changes in a commit to a single go module.\n\n" +
+	"Splitting instructions: https://git-scm.com/docs/git-rebase#_splitting_commits\n"
-	"You may learn more about how to split your existing commits at: https://git-scm.com/docs/git-rebase#_splitting_commits\n"
 
 // Ignore span pattern defines a regular expression pattern that, when matched,
 // causes this check to be ignored.
@@ -62,16 +61,33 @@ type GitHubService interface {
 	ListCommits(prId int, options *github.ListOptions) ([]*github.RepositoryCommit, *github.Response, error)
 }
 
-func (repository GitHubRepository) GetPullRequest(prId int) (*github.PullRequest, *github.Response, error) {
+// GetPullRequest retrieves details about a pull request from GitHub API
-	return repository.client.PullRequests.Get(context.Background(), *repository.owner, *repository.repo, prId)
+func (repository GitHubRepository) GetPullRequest(prId int) (
+	*github.PullRequest, *github.Response, error) {
+	return repository.client.PullRequests.Get(
+		context.Background(),
+		*repository.owner,
+		*repository.repo,
+		prId)
 }
 
-func (repository GitHubRepository) GetCommit(commitSha string) (*github.RepositoryCommit, *github.Response, error) {
+// GetCommit retrieves commit details from GitHub API
-	return repository.client.Repositories.GetCommit(context.Background(), *repository.owner, *repository.repo, commitSha)
+func (repository GitHubRepository) GetCommit(commitSha string) (
+	*github.RepositoryCommit, *github.Response, error) {
+	return repository.client.Repositories.GetCommit(context.Background(),
+		*repository.owner,
+		*repository.repo,
+		commitSha)
 }
 
-func (repository GitHubRepository) ListCommits(prId int, options *github.ListOptions) ([]*github.RepositoryCommit, *github.Response, error) {
+// ListCommits lists commits in a PR via GitHub API
-	return repository.client.PullRequests.ListCommits(context.Background(), *repository.owner, *repository.repo, prId, options)
+func (repository GitHubRepository) ListCommits(prId int, options *github.ListOptions) (
+	[]*github.RepositoryCommit, *github.Response, error) {
+	return repository.client.PullRequests.ListCommits(context.Background(),
+		*repository.owner,
+		*repository.repo,
+		prId,
+		options)
 }
 
 func main() {
@@ -145,7 +161,7 @@ func StringAllowsModuleSpan(body string) (bool, error) {
 	return regexp.MatchString(ignoreSpanPattern, body)
 }
 
-// IsModuleSpanAllowed tests a Pull Requests description for a regular
+// ModuleSpanAllowed tests a Pull Requests description for a regular
 // expression. If the expression matches then spanning modules are allowed.
 func ModuleSpanAllowed(repository GitHubService, pullId int) (bool, error) {
 
@@ -163,9 +179,6 @@ func ModuleSpanAllowed(repository GitHubService, pullId int) (bool, error) {
 // GetCommitChanges looks up a github commit by SHA and returns a Changeset
 // containing the modified files in the specified commit.
 func GetCommitChanges(repository GitHubService, commitSha string) (*Changeset, error) {
-
-	// Note: There are multiple ways to pull a github commit object
-	// we want a RepositoryCommit.
 	commit, _, err := repository.GetCommit(commitSha)
 
 	if err != nil {
@@ -210,7 +223,7 @@ func GetPullRequestCommits(repository GitHubService, pullrequest int) ([]*Change
 	return changesetResults, nil
 }
 
-// IsPullRequestSpanningPathList tests if a pull request spans multiple
+// PullRequestSpanningPathList tests if a pull request spans multiple
 // directory paths
 func PullRequestSpanningPathList(repository GitHubService, pullrequest int, paths []string) (bool, []*Changeset, error) {
 	// Create a buffer for commits
@@ -237,7 +250,7 @@ func PullRequestSpanningPathList(repository GitHubService, pullrequest int, path
 	return spanningChangesExist, changesets, nil
 }
 
-// IsChangesetSpanningPathList tests if a changeset is spanning
+// ChangesetSpanningPathList tests if a changeset is spanning
 // multiple directory paths.
 func ChangesetSpanningPathList(changeset *Changeset, paths []string) bool {
 	matchedPath := ""
@@ -254,6 +267,5 @@ func ChangesetSpanningPathList(changeset *Changeset, paths []string) bool {
 		}
 	}
 
-	// If more than 1 matched paths then the changeset spans paths
 	return false
 }