Implement noMergeCommits

src/domains/rules/NoMergeCommits.tests.ts

@@ -0,0 +1,71 @@
+import { describe, expect, it } from "vitest"
+import { fakeCommitFactory } from "#commits/Commit.fixtures.ts"
+import { fakeConfiguration } from "#configurations/Configuration.fixtures.ts"
+import { commitConcern } from "#rules/concerns/CommitConcern.ts"
+import type { Concerns } from "#rules/concerns/Concern.ts"
+import { noMergeCommits } from "#rules/NoMergeCommits.ts"
+import { ruleContext } from "#rules/Rule.ts"
+import { fakeCommitSha } from "#types/CommitSha.fixtures.ts"
+import type { CommitSha } from "#types/CommitSha.ts"
+
+const enabled = ruleContext("noMergeCommits")
+
+const fakeCommit = fakeCommitFactory(fakeConfiguration())
+
+describe.each`
+	parents                                                | subjectLine
+	${[fakeCommitSha(), fakeCommitSha()]}                  | ${"Merge branch 'main' into bugfix/dance-party-playlist"}
+	${[fakeCommitSha(), fakeCommitSha()]}                  | ${"Merge pull request #440 from renovate/battle-shell-7.x"}
+	${[fakeCommitSha(), fakeCommitSha(), fakeCommitSha()]} | ${"amend! Merge branch 'feature/new-coffee-machine' into feature/office-overhaul"}
+	${[fakeCommitSha(), fakeCommitSha(), fakeCommitSha()]} | ${"Keep my branch up to date"}
+`(
+	"when the commit is a merge commit with $parents.length parents and has a subject line of $subjectLine",
+	(props: { parents: Array<CommitSha>; subjectLine: string }) => {
+		const commit = fakeCommit({ message: props.subjectLine, parents: props.parents })
+
+		describe("and the rule is enabled", () => {
+			const actualConcerns = noMergeCommits([commit], enabled.options)
+
+			it("raises a concern about the entire commit", () => {
+				expect(actualConcerns).toEqual<Concerns>([commitConcern(enabled, commit.sha)])
+			})
+		})
+
+		describe("and the rule is disabled", () => {
+			const actualConcerns = noMergeCommits([commit], null)
+
+			it("does not raise any concerns", () => {
+				expect(actualConcerns).toEqual<Concerns>([])
+			})
+		})
+	},
+)
+
+describe.each`
+	parents              | subjectLine
+	${[]}                | ${"init"}
+	${[]}                | ${"Establish the repository"}
+	${[fakeCommitSha()]} | ${"just an ordinary commit"}
+	${[fakeCommitSha()]} | ${"Release the robot butler"}
+`(
+	"when the commit is not a merge commit and has a subject line of $subjectLine",
+	(props: { parents: Array<CommitSha>; subjectLine: string }) => {
+		const commit = fakeCommit({ message: props.subjectLine, parents: props.parents })
+
+		describe("and the rule is enabled", () => {
+			const actualConcerns = noMergeCommits([commit], enabled.options)
+
+			it("does not raise any concerns", () => {
+				expect(actualConcerns).toEqual<Concerns>([])
+			})
+		})
+
+		describe("and the rule is disabled", () => {
+			const actualConcerns = noMergeCommits([commit], null)
+
+			it("does not raise any concerns", () => {
+				expect(actualConcerns).toEqual<Concerns>([])
+			})
+		})
+	},
+)

src/domains/rules/NoMergeCommits.ts

@@ -1,9 +1,16 @@
 import type { Commit, Commits } from "#commits/Commit.ts"
+import { commitConcern } from "#rules/concerns/CommitConcern.ts"
 import type { Concern, Concerns } from "#rules/concerns/Concern.ts"
 import { type RuleContext, ruleContext } from "#rules/Rule.ts"
 import type { EmptyObject } from "#types/EmptyObject.ts"
 import { notNullish } from "#utilities/Arrays.ts"
 
+/**
+ * Verifies that the commit has at most one parent commit, thus disallowing merge commits.
+ *
+ * Avoiding merge commits makes the commit history linear and preserves the ability to rebase interactively.
+ * This helps to preserve the readability of the commit history and makes it easier to revert changes later.
+ */
 export function noMergeCommits(commits: Commits, options: EmptyObject | null): Concerns {
 	if (options === null) {
 		return []
@@ -13,6 +20,10 @@ export function noMergeCommits(commits: Commits, options: EmptyObject | null): C
 	return commits.map((commit) => verifyCommit(commit, rule)).filter(notNullish)
 }
 
-function verifyCommit(_commit: Commit, _rule: RuleContext): Concern | null {
-	throw new Error("The `noMergeCommits` rule has not been implemented yet") // TODO: To be implemented.
+function verifyCommit(commit: Commit, rule: RuleContext): Concern | null {
+	if (commit.isMergeCommit) {
+		return commitConcern(rule, commit.sha)
+	}
+
+	return null
 }

src/domains/rules/NoSquashMarkers.ts

@@ -7,7 +7,7 @@ import type { EmptyObject } from "#types/EmptyObject.ts"
 import { notNullish } from "#utilities/Arrays.ts"
 
 /**
- * Verifies that the subject line does not contain squash markers.
+ * Verifies that the subject line does not contain any squash marker.
  *
  * Combining squash commits with their ancestors makes the commit history cleaner and easier to read,
  * as it omits unnecessary diffs and increases the cohesion of commits. It also makes it easier to revert changes later.

src/domains/rules/UseConciseSubjectLines.tests.ts

@@ -33,35 +33,39 @@ describe.each`
 		const commit = fakeCommit({ message: props.subjectLine })
 
 		describe("and the rule is enabled with a maximum length of 20 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled20.options)
+
 			it("raises a concern about the characters that exceed the limit", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled20.options)
 				expect(actualConcerns).toEqual<Concerns>([
 					subjectLineConcern(enabled20, commit.sha, { range: props.expectedRange20 }),
 				])
 			})
 		})
 
 		describe("and the rule is enabled with a maximum length of 50 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled50.options)
+
 			it("raises a concern about the characters that exceed the limit", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled50.options)
 				expect(actualConcerns).toEqual<Concerns>([
 					subjectLineConcern(enabled50, commit.sha, { range: props.expectedRange50 }),
 				])
 			})
 		})
 
 		describe("and the rule is enabled with a maximum length of 72 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled72.options)
+
 			it("raises a concern about the characters that exceed the limit", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled72.options)
 				expect(actualConcerns).toEqual<Concerns>([
 					subjectLineConcern(enabled72, commit.sha, { range: props.expectedRange72 }),
 				])
 			})
 		})
 
 		describe("and the rule is disabled", () => {
+			const actualConcerns = useConciseSubjectLines([commit], null)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], null)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
@@ -84,33 +88,37 @@ describe.each`
 		const commit = fakeCommit({ message: props.subjectLine })
 
 		describe("and the rule is enabled with a maximum length of 20 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled20.options)
+
 			it("raises a concern about the characters that exceed the limit", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled20.options)
 				expect(actualConcerns).toEqual<Concerns>([
 					subjectLineConcern(enabled20, commit.sha, { range: props.expectedRange20 }),
 				])
 			})
 		})
 
 		describe("and the rule is enabled with a maximum length of 50 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled50.options)
+
 			it("raises a concern about the characters that exceed the limit", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled50.options)
 				expect(actualConcerns).toEqual<Concerns>([
 					subjectLineConcern(enabled50, commit.sha, { range: props.expectedRange50 }),
 				])
 			})
 		})
 
 		describe("and the rule is enabled with a maximum length of 72 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled72.options)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled72.options)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
 
 		describe("and the rule is disabled", () => {
+			const actualConcerns = useConciseSubjectLines([commit], null)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], null)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
@@ -135,31 +143,35 @@ describe.each`
 		const commit = fakeCommit({ message: props.subjectLine })
 
 		describe("and the rule is enabled with a maximum length of 20 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled20.options)
+
 			it("raises a concern about the characters that exceed the limit", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled20.options)
 				expect(actualConcerns).toEqual<Concerns>([
 					subjectLineConcern(enabled20, commit.sha, { range: props.expectedRange20 }),
 				])
 			})
 		})
 
 		describe("and the rule is enabled with a maximum length of 50 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled50.options)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled50.options)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
 
 		describe("and the rule is enabled with a maximum length of 72 characters", () => {
+			const actualConcerns = useConciseSubjectLines([commit], enabled72.options)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], enabled72.options)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
 
 		describe("and the rule is disabled", () => {
+			const actualConcerns = useConciseSubjectLines([commit], null)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], null)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
@@ -185,16 +197,18 @@ describe.each`
 		`(
 			"and the rule is enabled with a maximum length of $options.maxLength characters",
 			(context: RuleContext<"useConciseSubjectLines">) => {
+				const actualConcerns = useConciseSubjectLines([commit], context.options)
+
 				it("does not raise any concerns", () => {
-					const actualConcerns = useConciseSubjectLines([commit], context.options)
 					expect(actualConcerns).toEqual<Concerns>([])
 				})
 			},
 		)
 
 		describe("and the rule is disabled", () => {
+			const actualConcerns = useConciseSubjectLines([commit], null)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], null)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
@@ -218,16 +232,18 @@ describe.each`
 		`(
 			"and the rule is enabled with a maximum length of $options.maxLength characters",
 			(context: RuleContext<"useConciseSubjectLines">) => {
+				const actualConcerns = useConciseSubjectLines([commit], context.options)
+
 				it("does not raise any concerns", () => {
-					const actualConcerns = useConciseSubjectLines([commit], context.options)
 					expect(actualConcerns).toEqual<Concerns>([])
 				})
 			},
 		)
 
 		describe("and the rule is disabled", () => {
+			const actualConcerns = useConciseSubjectLines([commit], null)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], null)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
@@ -257,16 +273,18 @@ describe.each`
 		`(
 			"and the rule is enabled with a maximum length of $options.maxLength characters",
 			(context: RuleContext<"useConciseSubjectLines">) => {
+				const actualConcerns = useConciseSubjectLines([commit], context.options)
+
 				it("does not raise any concerns", () => {
-					const actualConcerns = useConciseSubjectLines([commit], context.options)
 					expect(actualConcerns).toEqual<Concerns>([])
 				})
 			},
 		)
 
 		describe("and the rule is disabled", () => {
+			const actualConcerns = useConciseSubjectLines([commit], null)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines([commit], null)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		})
@@ -299,8 +317,9 @@ describe("when verifying a set of multiple commits and some commits have long su
 	]
 
 	describe("and the rule is enabled with a maximum length of 20 characters", () => {
+		const actualConcerns = useConciseSubjectLines(commits, enabled20.options)
+
 		it("raises concerns about the commits whose subject lines exceed 20 characters", () => {
-			const actualConcerns = useConciseSubjectLines(commits, enabled20.options)
 			expect(actualConcerns).toEqual<Concerns>([
 				subjectLineConcern(enabled20, commits[0].sha, { range: [20, 52] }),
 				subjectLineConcern(enabled20, commits[1].sha, { range: [20, 24] }),
@@ -315,8 +334,9 @@ describe("when verifying a set of multiple commits and some commits have long su
 	})
 
 	describe("and the rule is enabled with a maximum length of 50 characters", () => {
+		const actualConcerns = useConciseSubjectLines(commits, enabled50.options)
+
 		it("raises concerns about the commits whose subject lines exceed 50 characters", () => {
-			const actualConcerns = useConciseSubjectLines(commits, enabled50.options)
 			expect(actualConcerns).toEqual<Concerns>([
 				subjectLineConcern(enabled50, commits[0].sha, { range: [50, 52] }),
 				subjectLineConcern(enabled50, commits[7].sha, { range: [50, 75] }),
@@ -326,8 +346,9 @@ describe("when verifying a set of multiple commits and some commits have long su
 	})
 
 	describe("and the rule is enabled with a maximum length of 72 characters", () => {
+		const actualConcerns = useConciseSubjectLines(commits, enabled72.options)
+
 		it("raises concerns about the commits whose subject lines exceed 72 characters", () => {
-			const actualConcerns = useConciseSubjectLines(commits, enabled72.options)
 			expect(actualConcerns).toEqual<Concerns>([
 				subjectLineConcern(enabled72, commits[7].sha, { range: [72, 75] }),
 				subjectLineConcern(enabled72, commits[11].sha, { range: [72, 76] }),
@@ -336,8 +357,9 @@ describe("when verifying a set of multiple commits and some commits have long su
 	})
 
 	describe("and the rule is disabled", () => {
+		const actualConcerns = useConciseSubjectLines(commits, null)
+
 		it("does not raise any concerns", () => {
-			const actualConcerns = useConciseSubjectLines(commits, null)
 			expect(actualConcerns).toEqual<Concerns>([])
 		})
 	})
@@ -359,16 +381,18 @@ describe("when verifying a set of multiple commits and all commits have concise
 	`(
 		"and the rule is enabled with a maximum length of $options.maxLength characters",
 		(context: RuleContext<"useConciseSubjectLines">) => {
+			const actualConcerns = useConciseSubjectLines(commits, context.options)
+
 			it("does not raise any concerns", () => {
-				const actualConcerns = useConciseSubjectLines(commits, context.options)
 				expect(actualConcerns).toEqual<Concerns>([])
 			})
 		},
 	)
 
 	describe("and the rule is disabled", () => {
+		const actualConcerns = useConciseSubjectLines(commits, null)
+
 		it("does not raise any concerns", () => {
-			const actualConcerns = useConciseSubjectLines(commits, null)
 			expect(actualConcerns).toEqual<Concerns>([])
 		})
 	})

src/domains/rules/concerns/CommitConcern.ts

@@ -0,0 +1,12 @@
+import type { RuleContext } from "#rules/Rule.ts"
+import type { CommitSha } from "#types/CommitSha.ts"
+
+export type CommitConcern = {
+	location: "commit"
+	rule: RuleContext
+	commitSha: CommitSha
+}
+
+export function commitConcern(rule: RuleContext, commitSha: CommitSha): CommitConcern {
+	return { location: "commit", rule, commitSha }
+}

src/domains/rules/concerns/Concern.ts

@@ -3,6 +3,7 @@ import type { Configuration } from "#configurations/Configuration.ts"
 import type { AuthorEmailAddressConcern } from "#rules/concerns/AuthorEmailAddressConcern.ts"
 import type { AuthorNameConcern } from "#rules/concerns/AuthorNameConcern.ts"
 import type { BodyLineConcern } from "#rules/concerns/BodyLineConcern.ts"
+import type { CommitConcern } from "#rules/concerns/CommitConcern.ts"
 import type { CommitterEmailAddressConcern } from "#rules/concerns/CommitterEmailAddressConcern.ts"
 import type { CommitterNameConcern } from "#rules/concerns/CommitterNameConcern.ts"
 import type { SubjectLineConcern } from "#rules/concerns/SubjectLineConcern.ts"
@@ -32,6 +33,7 @@ export type Concern =
 	| AuthorEmailAddressConcern
 	| AuthorNameConcern
 	| BodyLineConcern
+	| CommitConcern
 	| CommitterEmailAddressConcern
 	| CommitterNameConcern
 	| SubjectLineConcern