gen_stub: Fix handling of escape sequences in generated C strings

When handling sequences like this in a stub:

```php
<?php
class Whatever {
    public static string $foobar1 = "CCC \n\r\t\v\e\f\\\$\"\101\x41\u{41} CCC";
    public static string $foobar2 = 'CCC \n\r\t\v\e\f\\\$\"\101\x41\u{41} CCC';
}
```

...properly generate C headers that properly escape the string.
Otherwise, the differing escaping rules and differences between PHP's
single and double quoted strings could lead to mangled headers.

The output of these strings after the stub has been generated:

```
string(22) "BEGIN

	��\$"AAA END"
string(43) "BEGIN \n\r\t\v\e\f\\\\$\"\101\x41\u{41} END"
```

And the generated arginfo:

```c
        zval property_doubleQuoteEscaped_default_value;
        zend_string *property_doubleQuoteEscaped_default_value_str = zend_string_init("BEGIN \n\r\t\v\x1b\f\\$\"AAA END", strlen("BEGIN \n\r\t\v\x1b\f\\$\"AAA END"), 1);
pp      ZVAL_STR(&property_doubleQuoteEscaped_default_value, property_doubleQuoteEscaped_default_value_str);
        zend_string *property_doubleQuoteEscaped_name = zend_string_init("doubleQuoteEscaped", sizeof("doubleQuoteEscaped") - 1, true);
        zend_declare_typed_property(class_entry, property_doubleQuoteEscaped_name, &property_doubleQuoteEscaped_default_value, ZEND_ACC_PUBLIC|ZEND_ACC_STATIC, NULL, (zend_type) ZEND_TYPE_INIT_MASK(MAY_BE_STRING));
        zend_string_release_ex(property_doubleQuoteEscaped_name, true);

        zval property_singleQuoteEscaped_default_value;
        zend_string *property_singleQuoteEscaped_default_value_str = zend_string_init("BEGIN \\n\\r\\t\\v\\e\\f\\\\\\\\$\\\"\\101\\x41\\u{41} END", strlen("BEGIN \\n\\r\\t\\v\\e\\f\\\\\\\\$\\\"\\101\\x41\\u{41} END"), 1);
        ZVAL_STR(&property_singleQuoteEscaped_default_value, property_singleQuoteEscaped_default_value_str);
        zend_string *property_singleQuoteEscaped_name = zend_string_init("singleQuoteEscaped", sizeof("singleQuoteEscaped") - 1, true);
        zend_declare_typed_property(class_entry, property_singleQuoteEscaped_name, &property_singleQuoteEscaped_default_value, ZEND_ACC_PUBLIC|ZEND_ACC_STATIC, NULL, (zend_type) ZEND_TYPE_INIT_MASK(MAY_BE_STRING));
        zend_string_release_ex(property_singleQuoteEscaped_name, true);
```

Note that the PHP escape sequence "\$" will be handled in a special
manner to avoid providing it to C, to avoid C compiler warnings.

Tests are included via the zend_test stub and a phpt file to ensure that
the escape sequences match.

Fixes GH-22169.

Author: NattyNarwhal

build/gen_stub.php

@@ -2344,9 +2344,28 @@ public function getCExpr(): ?string
         // $this->expr has all its PHP constants replaced by C constants
         $prettyPrinter = new Standard;
         $expr = $prettyPrinter->prettyPrintExpr($this->expr);
-        // PHP single-quote to C double-quote string
         if ($this->type->isString()) {
-            $expr = preg_replace("/(^'|'$)/", '"', $expr);
+            // The string in $expr has had the octal, hex, and unicode
+            // backslash sequences already applied for double-quoted strings,
+            // but not the other sequences.
+            //
+            // PHP has single quote strings, C doesn't (they're one char).
+            // Single-quoted strings need handling to replace their escapes
+            // with the double-quoted equivalent; namely single quote escapes.
+            //
+            // Double-quoted strings have similar escape sequences as C does,
+            // so we can pass them through directly. However, C does *not*
+            // support the \$ escape sequence (in ""), so strip that. Variable
+            // interpolation shouldn't be possible in a stub, so we don't need
+            // to worry about mangling such a case.
+            if (preg_match("/(^'|'$)/", $expr)) {
+                $expr = substr($expr, 1, -1); // strip quotes, readd later
+                $expr = str_replace("\\'", "'", $expr);
+                $expr = addcslashes($expr, "\\\"");
+                $expr = "\"$expr\"";
+            } else {
+                $expr = str_replace('\$', "$", $expr);
+            }
         }
         return $expr[0] == '"' ? $expr : preg_replace('(\bnull\b)', 'NULL', str_replace('\\', '', $expr));
     }

ext/zend_test/test.stub.php

@@ -57,6 +57,12 @@ class _ZendTestClass implements _ZendTestInterface {
         public static $_StaticProp;
         public static int $staticIntProp = 123;
 
+        /* If there's a problem with escapes in quotes in generated headers,
+         * the generated header won't compile. (tests/gh22169.phpt) */
+        public static string $doubleQuoteEscaped = "BEGIN \n\r\t\v\e\f\\\$\"\101\x41\u{41} END";
+        public static string $singleQuoteEscaped = 'BEGIN \n\r\t\v\e\f\\\$\"\101\x41\u{41} END';
+        public static string $escapeInterpolated = "begin \$ \\$ end";
+
         public int $intProp = 123;
         public ?stdClass $classProp = null;
         public stdClass|Iterator|null $classUnionProp = null;

ext/zend_test/test_arginfo.h

@@ -0,0 +1,22 @@
+--TEST--
+GH-22169: Ensure escaped strings in stubs are valid
+--EXTENSIONS--
+zend_test
+--FILE--
+<?php
+
+// Avoid funny control characters in output...
+// "BEGIN "         424547494e20
+// "\n\r\t\v\e\f"   0a0d090b1b0c
+// "\\\$\""         5c2422
+// "\101\x41\u{41}" 414141
+// " END"           20454e44
+var_dump(bin2hex(_ZendTestClass::$doubleQuoteEscaped));
+var_dump(_ZendTestClass::$singleQuoteEscaped);
+var_dump(_ZendTestClass::$escapeInterpolated);
+?>
+--EXPECT--
+string(44) "424547494e200a0d090b1b0c5c242241414120454e44"
+string(43) "BEGIN \n\r\t\v\e\f\\\\$\"\101\x41\u{41} END"
+string(14) "begin $ \$ end"
+