From aa9fd9688870164ebf912cc32203940c94bb286f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juho=20Veps=C3=A4l=C3=A4inen?= <bebraw@gmail.com>
Date: Sat, 12 Dec 2020 11:47:31 +0100
Subject: [PATCH] feat: Throw if trying to append/prepend non-arrays

---
 src/index.ts                  | 18 +++++--
 test/merge-with-rules.test.ts | 98 +++++++++++++++++++++++++++++++++++
 2 files changed, 112 insertions(+), 4 deletions(-)

diff --git a/src/index.ts b/src/index.ts
index 7fec961..af445b5 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -177,10 +177,14 @@ function mergeWithRule({
           });
           break;
         case CustomizeRule.Append:
+          const appendValue = last(bMatches)[k];
+
+          if (!isArray(v) || !isArray(appendValue)) {
+            throw new TypeError("Trying to append non-arrays");
+          }
+
           ret[k] =
-            bMatches.length > 0
-              ? (v as Array<any>).concat(last(bMatches)[k])
-              : v;
+            bMatches.length > 0 ? (v as Array<any>).concat(appendValue) : v;
           break;
         case CustomizeRule.Merge:
           const lastValue = last(bMatches)[k];
@@ -193,7 +197,13 @@ function mergeWithRule({
           ret[k] = { ...v, ...lastValue };
           break;
         case CustomizeRule.Prepend:
-          ret[k] = bMatches.length > 0 ? last(bMatches)[k].concat(v) : v;
+          const prependValue = last(bMatches)[k];
+
+          if (!isArray(v) || !isArray(prependValue)) {
+            throw new TypeError("Trying to prepend non-arrays");
+          }
+
+          ret[k] = bMatches.length > 0 ? prependValue.concat(v) : v;
           break;
         case CustomizeRule.Replace:
           ret[k] = bMatches.length > 0 ? last(bMatches)[k] : v;
diff --git a/test/merge-with-rules.test.ts b/test/merge-with-rules.test.ts
index 3b8b4e7..ea44ba6 100644
--- a/test/merge-with-rules.test.ts
+++ b/test/merge-with-rules.test.ts
@@ -723,6 +723,104 @@ describe("Merge with rules", function () {
     });
   });
 
+  it("should throw if trying to append non-arrays", function () {
+    const _mergeWithExplicitRule = mergeWithRules({
+      module: {
+        rules: {
+          test: CustomizeRule.Match,
+          use: {
+            loader: CustomizeRule.Match,
+            options: CustomizeRule.Append,
+          },
+        },
+      },
+    });
+    const a = {
+      resolve: { extensions: [".js"] },
+      module: {
+        rules: [
+          {
+            test: /\.css$/,
+            use: [
+              { loader: "style-loader", options: {} },
+              { loader: "sass-loader" },
+            ],
+          },
+        ],
+      },
+    };
+    const b = {
+      resolve: { extensions: [".css"] },
+      module: {
+        rules: [
+          {
+            test: /\.css$/,
+            use: [
+              {
+                loader: "style-loader",
+                options: {},
+              },
+            ],
+          },
+        ],
+      },
+    };
+
+    assert.throws(() => _mergeWithExplicitRule(a, b), {
+      name: "TypeError",
+      message: "Trying to append non-arrays",
+    });
+  });
+
+  it("should throw if trying to prepend non-arrays", function () {
+    const _mergeWithExplicitRule = mergeWithRules({
+      module: {
+        rules: {
+          test: CustomizeRule.Match,
+          use: {
+            loader: CustomizeRule.Match,
+            options: CustomizeRule.Prepend,
+          },
+        },
+      },
+    });
+    const a = {
+      resolve: { extensions: [".js"] },
+      module: {
+        rules: [
+          {
+            test: /\.css$/,
+            use: [
+              { loader: "style-loader", options: {} },
+              { loader: "sass-loader" },
+            ],
+          },
+        ],
+      },
+    };
+    const b = {
+      resolve: { extensions: [".css"] },
+      module: {
+        rules: [
+          {
+            test: /\.css$/,
+            use: [
+              {
+                loader: "style-loader",
+                options: {},
+              },
+            ],
+          },
+        ],
+      },
+    };
+
+    assert.throws(() => _mergeWithExplicitRule(a, b), {
+      name: "TypeError",
+      message: "Trying to prepend non-arrays",
+    });
+  });
+
   it("should work with multi-level match (#153)", function () {
     const a = {
       module: {