Add script/extract_functions.php

Author: zonuexe

Diff for: .gitignore

@@ -5,3 +5,4 @@
 /.keg/*
 /.php-cs-fixer.cache
 php-mode-autoloads.el
+php_manual_en.json

Diff for: script/README.md

@@ -0,0 +1,40 @@
+
+# Maintenance script for PHP Mode
+
+These scripts are provided for maintenance of PHP Mode.
+
+## Extract PHP Functions
+
+This script extract PHP function names from <http://doc.php.net/downloads/json/php_manual_en.json>.
+
+### Usage
+
+```
+Usage:
+	./script/extract_functions.php count < php_manual_en.json
+	./script/extract_functions.php modules < php_manual_en.json
+	./script/extract_functions.php functions < php_manual_en.json > result.json
+	./script/extract_functions.php functions-sexp < php_manual_en.json > result.el
+```
+
+### Data
+
+A pattern for grouping function modules by function-id is written in `data/module_id_prefixes.php`.
+
+ * All entries are combined as prefix matching patterns
+ * The meanings of `.` and `\.` (matches) in the regular expression are swapped
+   * `\.` matches any one character
+   * `.` matches only `"."`
+ * An alphanumeric-terminated entry requires an exact match
+   * Other entries require a [`\b`(word boundary)](https://www.php.net/manual/regexp.reference.escape.php) at the end
+
+```php
+return [
+    'apache' => [
+        'function.apache-', // matches all "apache-" prefixed IDs
+        'function.virtual', // matches only "function.virtual"
+    ],
+    'bcmath' => [
+        'function.bc\.+',   // matches "function.bcadd", "function.bccomp", ...etc
+    ],
+```