From b4bd83acf54a8d1d24ceac3089b16f1e90f6a5ea Mon Sep 17 00:00:00 2001
From: "Nicholas C. Zakas" <nicholas@humanwhocodes.com>
Date: Thu, 16 Sep 2021 10:34:05 -0700
Subject: [PATCH] Update: Suggest missing rule in flat config (fixes #14027)

---
 lib/config/rule-validator.js          | 26 ++++++++++++++++------
 tests/lib/config/flat-config-array.js | 32 +++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 7 deletions(-)

diff --git a/lib/config/rule-validator.js b/lib/config/rule-validator.js
index fe1aa863bfd..6f25f86b9c1 100644
--- a/lib/config/rule-validator.js
+++ b/lib/config/rule-validator.js
@@ -35,16 +35,28 @@ function findRuleDefinition(ruleId, config) {
         pluginName = ruleIdParts.join("/");
     }
 
-    if (!config.plugins || !config.plugins[pluginName]) {
-        throw new TypeError(`Key "rules": Key "${ruleId}": Could not find plugin "${pluginName}".`);
-    }
+    if (config?.plugins) {
 
-    if (!config.plugins[pluginName].rules || !config.plugins[pluginName].rules[ruleName]) {
-        throw new TypeError(`Key "rules": Key "${ruleId}": Could not find "${ruleName}" in plugin "${pluginName}".`);
-    }
+        // first check for exact rule match
+        if (config.plugins?.[pluginName]?.rules?.[ruleName]) {
+            return config.plugins[pluginName].rules[ruleName];
+        }
 
-    return config.plugins[pluginName].rules[ruleName];
+        let errorMessage = `Key "rules": Key "${ruleId}": Could not find "${ruleName}" in plugin "${pluginName}".`;
+
+        // otherwise, let's see if we can find the rule name elsewhere
+        for (const [otherPluginName, plugin] of Object.entries(config.plugins)) {
+            if (plugin?.rules?.[ruleName]) {
+                errorMessage += ` Did you mean "${otherPluginName}/${ruleName}"?`;
+                break;
+            }
+        }
+
+        throw new TypeError(errorMessage);
+
+    }
 
+    throw new TypeError(`Key "rules": Key "${ruleId}": Could not find plugin "${pluginName}".`);
 }
 
 /**
diff --git a/tests/lib/config/flat-config-array.js b/tests/lib/config/flat-config-array.js
index fd89f8d972c..e43e195ac41 100644
--- a/tests/lib/config/flat-config-array.js
+++ b/tests/lib/config/flat-config-array.js
@@ -56,6 +56,16 @@ const baseConfig = {
                     }
                 }
             }
+        },
+        test1: {
+            rules: {
+                match: {}
+            }
+        },
+        test2: {
+            rules: {
+                nomatch: {}
+            }
         }
     }
 };
@@ -1278,6 +1288,28 @@ describe("FlatConfigArray", () => {
                 ], "Key \"rules\": Key \"foo\": Expected severity of \"off\", 0, \"warn\", 1, \"error\", or 2.");
             });
 
+            it("should error when rule doesn't exist", async () => {
+
+                await assertInvalidConfig([
+                    {
+                        rules: {
+                            foox: [1, "bar"]
+                        }
+                    }
+                ], /Key "rules": Key "foox": Could not find "foox" in plugin "@"./u);
+            });
+
+            it("should error and suggest alternative when rule doesn't exist", async () => {
+
+                await assertInvalidConfig([
+                    {
+                        rules: {
+                            "test2/match": "error"
+                        }
+                    }
+                ], /Key "rules": Key "test2\/match": Could not find "match" in plugin "test2"\. Did you mean "test1\/match"\?/u);
+            });
+
             it("should error when rule options don't match schema", async () => {
 
                 await assertInvalidConfig([