feat: add number of commits check

Signed-off-by: Andrew Rynhard <andrew@andrewrynhard.com>

.conform.yaml

@@ -1,25 +1,26 @@
 policies:
-- type: commit
-  spec:
-    headerLength: 89
-    dco: true
-    gpg: false
-    imperative: true
-    conventional:
-      types:
-      - chore
-      - docs
-      - perf
-      - refactor
-      - style
-      - test
-      scopes:
-      - policy
-- type: license
-  spec:
-    includeSuffixes:
-    - .go
-    header: |
-      /* This Source Code Form is subject to the terms of the Mozilla Public
-       * License, v. 2.0. If a copy of the MPL was not distributed with this
-       * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+  - type: commit
+    spec:
+      headerLength: 89
+      dco: true
+      gpg: false
+      imperative: true
+      maximumOfOneCommit: true
+      conventional:
+        types:
+          - chore
+          - docs
+          - perf
+          - refactor
+          - style
+          - test
+        scopes:
+          - policy
+  - type: license
+    spec:
+      includeSuffixes:
+        - .go
+      header: |
+        /* This Source Code Form is subject to the terms of the Mozilla Public
+         * License, v. 2.0. If a copy of the MPL was not distributed with this
+         * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

internal/git/git.go

@@ -14,6 +14,7 @@ import (
 	"gopkg.in/src-d/go-git.v4/config"
 	"gopkg.in/src-d/go-git.v4/plumbing"
 	"gopkg.in/src-d/go-git.v4/plumbing/object"
+	"gopkg.in/src-d/go-git.v4/plumbing/storer"
 )
 
 // Git is a helper for git.
@@ -134,3 +135,38 @@ func (g *Git) SHA() (sha string, err error) {
 
 	return sha, nil
 }
+
+// AheadBehind returns the number of commits that HEAD is ahead and behind
+// relative to the specified ref.
+func (g *Git) AheadBehind(ref string) (ahead int, behind int, err error) {
+	ref1, err := g.repo.Reference(plumbing.ReferenceName(ref), false)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	ref2, err := g.repo.Head()
+	if err != nil {
+		return 0, 0, err
+	}
+
+	commit2, err := object.GetCommit(g.repo.Storer, ref2.Hash())
+	if err != nil {
+		return 0, 0, nil
+	}
+
+	var count int
+	iter := object.NewCommitPreorderIter(commit2, nil, nil)
+	err = iter.ForEach(func(comm *object.Commit) error {
+		if comm.Hash != ref1.Hash() {
+			count++
+			return nil
+		}
+
+		return storer.ErrStop
+	})
+	if err != nil {
+		return 0, 0, nil
+	}
+
+	return count, 0, nil
+}

internal/policy/commit/check_number_of_commits.go

@@ -0,0 +1,57 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package commit
+
+import (
+	"fmt"
+
+	"github.com/autonomy/conform/internal/git"
+	"github.com/autonomy/conform/internal/policy"
+	"github.com/pkg/errors"
+)
+
+// NumberOfCommits enforces a maximum number of charcters on the commit
+// header.
+type NumberOfCommits struct {
+	ref    string
+	ahead  int
+	errors []error
+}
+
+// Name returns the name of the check.
+func (h NumberOfCommits) Name() string {
+	return "Number of Commits"
+}
+
+// Message returns to check message.
+func (h NumberOfCommits) Message() string {
+	return fmt.Sprintf("HEAD is %d commit(s) ahead of %s", h.ahead, h.ref)
+}
+
+// Errors returns any violations of the check.
+func (h NumberOfCommits) Errors() []error {
+	return h.errors
+}
+
+// ValidateNumberOfCommits checks the header length.
+func (c Commit) ValidateNumberOfCommits(g *git.Git, ref string) policy.Check {
+	check := &NumberOfCommits{
+		ref: ref,
+	}
+
+	var err error
+	check.ahead, _, err = g.AheadBehind(ref)
+	if err != nil {
+		check.errors = append(check.errors, err)
+		return check
+	}
+
+	if check.ahead > 1 {
+		check.errors = append(check.errors, errors.Errorf("HEAD is %d commit(s) ahead of %s", check.ahead, ref))
+		return check
+	}
+
+	return check
+}

internal/policy/commit/commit.go

@@ -26,6 +26,9 @@ type Commit struct {
 	// Imperative enforces the use of imperative verbs as the first word of a
 	// commit message.
 	Imperative bool `mapstructure:"imperative"`
+	// MaximumOfOneCommit enforces that the current commit is only one commit
+	// ahead of a specified ref.
+	MaximumOfOneCommit bool `mapstructure:"maximumOfOneCommit"`
 	// Conventional is the user specified settings for conventional commits.
 	Conventional *Conventional `mapstructure:"conventional"`
 
@@ -73,6 +76,7 @@ func (c *Commit) Compliance(options *policy.Options) (*policy.Report, error) {
 	if c.GPG {
 		report.AddCheck(c.ValidateGPGSign(g))
 	}
+
 	if c.Imperative {
 		report.AddCheck(c.ValidateImperative())
 	}
@@ -81,6 +85,10 @@ func (c *Commit) Compliance(options *policy.Options) (*policy.Report, error) {
 		report.AddCheck(c.ValidateConventionalCommit())
 	}
 
+	if c.MaximumOfOneCommit {
+		report.AddCheck(c.ValidateNumberOfCommits(g, "refs/heads/master"))
+	}
+
 	return report, nil
 }