Use values, not pointers, in GraphQL queries (#65)

I'm not sure if this is needed, but after switching how commits are
loaded in 1.7.0, we started seeing weird race-condition-like issues
where the program would crash or randomly be missing information. One
incidental change was that commits switched from being values to being
pointers in the GraphQL query struct.

pull/github.go

@@ -157,7 +157,7 @@ func (ghc *GitHubContext) Commits() ([]*Commit, error) {
 					Commit struct {
 						History struct {
 							PageInfo v4PageInfo
-							Nodes    []*v4Commit
+							Nodes    []v4Commit
 						} `graphql:"history(first: $limit, after: $cursor)"`
 					} `graphql:"... on Commit"`
 				} `graphql:"object(oid: $oid)"`
@@ -172,7 +172,7 @@ func (ghc *GitHubContext) Commits() ([]*Commit, error) {
 			"cursor": (*githubv4.String)(nil),
 		}
 
-		var commits []*v4Commit
+		var commits []v4Commit
 		for {
 			qvars["limit"] = githubv4.Int(min(totalCommits-len(commits), MaxPageSize))
 			if err := ghc.v4client.Query(ghc.ctx, &q, qvars); err != nil {
@@ -247,7 +247,7 @@ func (ghc *GitHubContext) TargetCommits() ([]*Commit, error) {
 					Target struct {
 						Commit struct {
 							History struct {
-								Nodes []*v4Commit
+								Nodes []v4Commit
 							} `graphql:"history(first: $limit)"`
 						} `graphql:"... on Commit"`
 					}
@@ -283,12 +283,12 @@ func (ghc *GitHubContext) loadCommentsAndReviews() error {
 			PullRequest struct {
 				Comments struct {
 					PageInfo v4PageInfo
-					Nodes    []*v4IssueComment
+					Nodes    []v4IssueComment
 				} `graphql:"comments(first: 100, after: $commentCursor)"`
 
 				Reviews struct {
 					PageInfo v4PageInfo
-					Nodes    []*v4PullRequestReview
+					Nodes    []v4PullRequestReview
 				} `graphql:"reviews(first: 100, after: $reviewCursor, states: [APPROVED, CHANGES_REQUESTED])"`
 			} `graphql:"pullRequest(number: $number)"`
 		} `graphql:"repository(owner: $owner, name: $name)"`
@@ -423,13 +423,14 @@ func (c *v4Commit) ToCommit() *Commit {
 // to all other commits in that batch. It assumes the commits slice is in
 // descending chronologic order (latest commit at the start), which is the
 // default for `git log` and most GitHub APIs.
-func backfillPushedDate(commits []*v4Commit) {
+func backfillPushedDate(commits []v4Commit) {
 	var lastPushed *time.Time
-	for _, c := range commits {
+	for i, c := range commits {
 		if c.PushedDate != nil {
 			lastPushed = c.PushedDate
 		} else {
 			c.PushedDate = lastPushed
+			commits[i] = c
 		}
 	}
 }