Move internal modules to “internal” folder.

.internal/mergeData.js

@@ -0,0 +1,92 @@
+import composeArgs from './.internal/composeArgs.js';
+import composeArgsRight from './.internal/composeArgsRight.js';
+import replaceHolders from './.internal/replaceHolders.js';
+
+/** Used as the internal argument placeholder. */
+const PLACEHOLDER = '__lodash_placeholder__';
+
+/** Used to compose bitmasks for function metadata. */
+const WRAP_BIND_FLAG = 1;
+const WRAP_BIND_KEY_FLAG = 2;
+const WRAP_CURRY_BOUND_FLAG = 4;
+const WRAP_CURRY_FLAG = 8;
+const WRAP_ARY_FLAG = 128;
+const WRAP_REARG_FLAG = 256;
+
+/* Built-in method references for those with the same name as other `lodash` methods. */
+const nativeMin = Math.min;
+
+/**
+ * Merges the function metadata of `source` into `data`.
+ *
+ * Merging metadata reduces the number of wrappers used to invoke a function.
+ * This is possible because methods like `bind`, `curry`, and `partial`
+ * may be applied regardless of execution order. Methods like `ary` and
+ * `rearg` modify function arguments, making the order in which they are
+ * executed important, preventing the merging of metadata. However, we make
+ * an exception for a safe combined case where curried functions have `ary`
+ * and or `rearg` applied.
+ *
+ * @private
+ * @param {Array} data The destination metadata.
+ * @param {Array} source The source metadata.
+ * @returns {Array} Returns `data`.
+ */
+function mergeData(data, source) {
+  const bitmask = data[1];
+  const srcBitmask = source[1];
+
+  let newBitmask = bitmask | srcBitmask;
+  const isCommon = newBitmask < (WRAP_BIND_FLAG | WRAP_BIND_KEY_FLAG | WRAP_ARY_FLAG);
+
+  const isCombo =
+    ((srcBitmask == WRAP_ARY_FLAG) && (bitmask == WRAP_CURRY_FLAG)) ||
+    ((srcBitmask == WRAP_ARY_FLAG) && (bitmask == WRAP_REARG_FLAG) && (data[7].length <= source[8])) ||
+    ((srcBitmask == (WRAP_ARY_FLAG | WRAP_REARG_FLAG)) && (source[7].length <= source[8]) && (bitmask == WRAP_CURRY_FLAG));
+
+  // Exit early if metadata can't be merged.
+  if (!(isCommon || isCombo)) {
+    return data;
+  }
+  // Use source `thisArg` if available.
+  if (srcBitmask & WRAP_BIND_FLAG) {
+    data[2] = source[2];
+    // Set when currying a bound function.
+    newBitmask |= bitmask & WRAP_BIND_FLAG ? 0 : WRAP_CURRY_BOUND_FLAG;
+  }
+  // Compose partial arguments.
+  let partials;
+  let value = source[3];
+  if (value) {
+    partials = data[3];
+    data[3] = partials ? composeArgs(partials, value, source[4]) : value;
+    data[4] = partials ? replaceHolders(data[3], PLACEHOLDER) : source[4];
+  }
+  // Compose partial right arguments.
+  value = source[5];
+  if (value) {
+    partials = data[5];
+    data[5] = partials ? composeArgsRight(partials, value, source[6]) : value;
+    data[6] = partials ? replaceHolders(data[5], PLACEHOLDER) : source[6];
+  }
+  // Use source `argPos` if available.
+  value = source[7];
+  if (value) {
+    data[7] = value;
+  }
+  // Use source `ary` if it's smaller.
+  if (srcBitmask & WRAP_ARY_FLAG) {
+    data[8] = data[8] == null ? source[8] : nativeMin(data[8], source[8]);
+  }
+  // Use source `arity` if one is not provided.
+  if (data[9] == null) {
+    data[9] = source[9];
+  }
+  // Use source `func` and merge bitmasks.
+  data[0] = source[0];
+  data[1] = newBitmask;
+
+  return data;
+}
+
+export default mergeData;