commitlint.config: add rule

Add default-revert-message rule.

commitlint.config.ts

@@ -50,11 +50,15 @@ module.exports = {
         // disabled because most of the time it doesn't work, due to https://github.com/conventional-changelog/commitlint/issues/3404
         // and anyway we were using this rule only as a warning, not an error (because a scope is not required, e.g. when too broad)
         "type-empty": [RuleConfigSeverity.Disabled, "never"],
+        "default-revert-message": [RuleConfigSeverity.Error, "never"],
     },
+
+    // Commitlint automatically ignores some kinds of commits like Revert commit messages.
+    // We need to set this value to false to apply our rules on these messages.
+    defaultIgnores: false,
     plugins: [
         // TODO (ideas for more rules):
         // * Detect if paragraphs in body have been cropped too shortly (less than 64 chars), and suggest same auto-wrap command that body-soft-max-line-length suggests, since it unwraps and wraps (both).
-        // * Detect reverts which have not been elaborated.
         // * Reject some stupid obvious words: change, update, modify (if first word after colon, error; otherwise warning).
         // * Think of how to reject this shitty commit message: https://github.com/nblockchain/NOnion/pull/34/commits/9ffcb373a1147ed1c729e8aca4ffd30467255594
         // * Workflow: detect if wip commit in a branch not named "wip/*" or whose name contains "squashed".
@@ -139,6 +143,32 @@ module.exports = {
                     return Plugins.properIssueRefs(rawStr);
                 },
 
+                "default-revert-message": (
+                    {
+                        header,
+                        body,
+                    }: {
+                        header: any;
+                        body: any;
+                    },
+                    when: any
+                ) => {
+                    let bodyStr = Helpers.convertAnyToString(body, "body");
+                    let headerUncastedStr = Helpers.convertAnyToString(
+                        header,
+                        "header"
+                    );
+                    let headerStr = Helpers.assertNotNull(
+                        headerUncastedStr,
+                        notNullStringErrorMessage("header")
+                    );
+                    return Plugins.defaultRevertMessage(
+                        headerStr,
+                        bodyStr,
+                        when
+                    );
+                },
+
                 "title-uppercase": ({ header }: { header: any }) => {
                     let headerStr = Helpers.assertNotNull(
                         Helpers.convertAnyToString(header, "header"),

commitlint/plugins.ts

@@ -262,6 +262,44 @@ export abstract class Plugins {
         ];
     }
 
+    public static defaultRevertMessage(
+        headerStr: string,
+        bodyStr: string | null,
+        when: string
+    ) {
+        let offence = false;
+        let isRevertCommitMessage = headerStr.toLowerCase().includes("revert");
+
+        const negated = when === "never";
+
+        if (isRevertCommitMessage) {
+            let isDefaultRevertHeader =
+                headerStr.match(/^[Rr]evert ".+"$/) !== null;
+
+            if (isDefaultRevertHeader) {
+                if (bodyStr !== null) {
+                    let lines = bodyStr.split("\n");
+                    offence =
+                        // 40 is the length of git commit hash.
+                        lines.length == 1 &&
+                        lines[0].match(/^This reverts commit [^ ]{40}\.$/) !==
+                            null;
+                } else {
+                    offence = true;
+                }
+            }
+
+            offence = negated ? offence : !offence;
+        }
+        return [
+            !offence,
+            (negated
+                ? `Please explain why you're reverting`
+                : `Please don't change the default revert commit message`) +
+                Helpers.errMessageSuffix,
+        ];
+    }
+
     public static titleUppercase(headerStr: string) {
         let firstWord = headerStr.split(" ")[0];
         let offence =