Zend: suggest similar names for undefined function/class/method error

UPGRADING

@@ -113,6 +113,12 @@ PHP 8.7 UPGRADE NOTES
 13. Other Changes
 ========================================
 
+- Core:
+  . Errors for undefined functions, undefined methods and classes, interfaces
+    or traits that were not found now suggest a similarly named one, e.g.
+    'Call to undefined function strlenn() (did you mean strlen?)'. Code that
+    matches on the exact error message may need to be updated.
+
 ========================================
 14. Performance Improvements
 ========================================

Zend/tests/exceptions/bug31102.phpt

@@ -43,7 +43,7 @@ Caught: Test1::__construct
 Caught: {closure:%s:%d}
 {closure:%s:%d}(Test3,3)
 
-Fatal error: Uncaught Error: Class "Test3" not found in %s:%d
+Fatal error: Uncaught Error: Class "Test3" not found (did you mean "Test1"?) in %s:%d
 Stack trace:
 #0 %s(%d): eval()
 #1 {main}

Zend/tests/is_callable/bug69315.phpt

@@ -43,7 +43,7 @@ try {
 bool(false)
 bool(false)
 Error: Call to undefined function strlen()
-Error: Call to undefined function defined()
+Error: Call to undefined function defined() (did you mean define?)
 Error: Call to undefined function constant()
 Error: Call to undefined function call_user_func()
 Error: Call to undefined function is_string()

Zend/tests/name_suggestion/suggestion_undefined_class.phpt

@@ -0,0 +1,35 @@
+--TEST--
+Levenshtein suggestion for undefined class, interface and trait lookups
+--FILE--
+<?php
+// One edit away — should suggest
+try { new ArrayObjekt(); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+try { new StdClas(); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// One edit away for a longer name — should suggest
+try { new ArrayIteratr(); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Two edits away for a name >= 8 chars — adaptive threshold should suggest
+try { new ArryObjct(); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Completely wrong name — no suggestion
+try { new Unicorn(); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Interface
+try {
+    $c = new class() implements Countble {};
+} catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Trait
+try {
+    eval('class T { use NonExistntTrait; }');
+} catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+?>
+--EXPECTF--
+Error: Class "ArrayObjekt" not found (did you mean "ArrayObject"?)
+Error: Class "StdClas" not found (did you mean "stdClass"?)
+Error: Class "ArrayIteratr" not found (did you mean "ArrayIterator"?)
+Error: Class "ArryObjct" not found (did you mean "ArrayObject"?)
+Error: Class "Unicorn" not found
+Error: Interface "Countble" not found (did you mean "Countable"?)
+Error: Trait "NonExistntTrait" not found

Zend/tests/name_suggestion/suggestion_undefined_fcc.phpt

@@ -0,0 +1,28 @@
+--TEST--
+Levenshtein suggestion for undefined function in FCC context
+--FILE--
+<?php
+// Test 1: In default argument position
+
+function test(Closure $name = array_pussh(...)) {
+    var_dump($name);
+}
+
+try {
+    test();
+} catch (Error $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
+
+// Test 2: In constant initializer (via eval so the fatal can be caught for combined output)
+
+try {
+    eval("const Closure2 = strlenn(...);");
+} catch (Error $e) {
+    echo $e::class, ': ', $e->getMessage(), "\n";
+}
+
+?>
+--EXPECT--
+Error: Call to undefined function array_pussh() (did you mean array_push?)
+Error: Call to undefined function strlenn() (did you mean strlen?)

Zend/tests/name_suggestion/suggestion_undefined_function.phpt

@@ -0,0 +1,26 @@
+--TEST--
+Levenshtein suggestion for undefined function calls
+--FILE--
+<?php
+// One edit away — should suggest
+try { strlenn("x"); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// One edit away for a longer name — should suggest
+try { array_pussh([], 1); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Two edits away for a name >= 8 chars — adaptive threshold should suggest
+try { arry_pussh([], 1); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Completely wrong name — no suggestion
+try { nonexistentfunc(); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Dynamic call — same suggestion logic applies
+$f = "strlenx";
+try { $f("x"); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+?>
+--EXPECT--
+Error: Call to undefined function strlenn() (did you mean strlen?)
+Error: Call to undefined function array_pussh() (did you mean array_push?)
+Error: Call to undefined function arry_pussh() (did you mean array_push?)
+Error: Call to undefined function nonexistentfunc()
+Error: Call to undefined function strlenx() (did you mean strlen?)

Zend/tests/name_suggestion/suggestion_undefined_function_namespaced.phpt

@@ -0,0 +1,33 @@
+--TEST--
+Levenshtein suggestion for undefined function calls in a namespace
+--FILE--
+<?php
+namespace App;
+
+function helper() {}
+
+// Unqualified call — falls back to a similar global function
+try { strlenn("x"); } catch (\Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Unqualified call — similar function in the current namespace wins
+try { helpr(); } catch (\Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Qualified call — only namespaced functions are considered
+try { \App\helpr(); } catch (\Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+try { \App\strlenn("x"); } catch (\Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Dynamic call with a namespaced name
+$f = 'App\helpr';
+try { $f(); } catch (\Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// FCC in a default argument — falls back to a similar global function
+function test(\Closure $c = strlenn(...)) {}
+try { test(); } catch (\Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+?>
+--EXPECT--
+Error: Call to undefined function App\strlenn() (did you mean strlen?)
+Error: Call to undefined function App\helpr() (did you mean App\helper?)
+Error: Call to undefined function App\helpr() (did you mean App\helper?)
+Error: Call to undefined function App\strlenn()
+Error: Call to undefined function App\helpr() (did you mean App\helper?)
+Error: Call to undefined function App\strlenn() (did you mean strlen?)

Zend/tests/name_suggestion/suggestion_undefined_method.phpt

@@ -0,0 +1,29 @@
+--TEST--
+Levenshtein suggestion for undefined method calls
+--FILE--
+<?php
+class Calculator {
+    public function add(int $a, int $b): int { return $a + $b; }
+    public function subtract(int $a, int $b): int { return $a - $b; }
+    public function multiply(int $a, int $b): int { return $a * $b; }
+}
+
+$calc = new Calculator();
+
+// One edit away — should suggest
+try { $calc->addd(1, 2); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Two edits away for a name >= 8 chars — adaptive threshold should suggest
+try { $calc->subtarct(5, 3); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Completely wrong name — no suggestion
+try { $calc->nonexistent(); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+
+// Static call — same logic applies
+try { Calculator::addd(1, 2); } catch (Error $e) { echo $e::class, ': ', $e->getMessage(), "\n"; }
+?>
+--EXPECT--
+Error: Call to undefined method Calculator::addd() (did you mean add?)
+Error: Call to undefined method Calculator::subtarct() (did you mean subtract?)
+Error: Call to undefined method Calculator::nonexistent()
+Error: Call to undefined method Calculator::addd() (did you mean add?)

Zend/tests/nullsafe_operator/003.phpt

@@ -48,10 +48,10 @@ string(3) "bar"
 Warning: Undefined property: Foo::$baz in %s.php on line 20
 NULL
 string(3) "qux"
-Error: Call to undefined method Foo::quux()
+Error: Call to undefined method Foo::quux() (did you mean qux?)
 string(3) "bar"
 
 Warning: Undefined property: Foo::$baz in %s.php on line 29
 NULL
 string(3) "qux"
-Error: Call to undefined method Foo::quux()
+Error: Call to undefined method Foo::quux() (did you mean qux?)

Zend/tests/nullsafe_operator/033.phpt

@@ -48,7 +48,7 @@ string(3) "bar"
 Warning: Undefined property: Foo::$baz in %s.php on line 20
 string(0) ""
 string(3) "qux"
-Error: Call to undefined method Foo::quux()
+Error: Call to undefined method Foo::quux() (did you mean qux?)
 string(3) "bar"
 
 Warning: Undefined property: Foo::$baz in %s.php on line 29

Zend/zend_ast.c

@@ -18,6 +18,7 @@
 
 #include "zend_ast.h"
 #include "zend_API.h"
+#include "zend_execute.h"
 #include "zend_operators.h"
 #include "zend_language_parser.h"
 #include "zend_smart_str.h"
@@ -1259,7 +1260,20 @@ static zend_result ZEND_FASTCALL zend_ast_evaluate_inner(
 						}
 
 						if (!fptr) {
-							zend_throw_error(NULL, "Call to undefined function %s()", ZSTR_VAL(function_name));
+							zend_string *lc_name = zend_string_tolower(function_name);
+							zend_string *suggestion = zend_find_similar_function(ZSTR_VAL(lc_name), ZSTR_LEN(lc_name));
+							if (!suggestion && ast->child[0]->attr != ZEND_NAME_FQ) {
+								const char *backslash = zend_memrchr(ZSTR_VAL(lc_name), '\\', ZSTR_LEN(lc_name));
+								if (backslash) {
+									suggestion = zend_find_similar_function(backslash + 1, ZSTR_LEN(lc_name) - (backslash - ZSTR_VAL(lc_name) + 1));
+								}
+							}
+							if (suggestion) {
+								zend_throw_error(NULL, "Call to undefined function %s() (did you mean %s?)", ZSTR_VAL(function_name), ZSTR_VAL(suggestion));
+							} else {
+								zend_throw_error(NULL, "Call to undefined function %s()", ZSTR_VAL(function_name));
+							}
+							zend_string_release(lc_name);
 							return FAILURE;
 						}
 

Zend/zend_execute.c

@@ -2582,9 +2582,80 @@ ZEND_API ZEND_COLD zval* ZEND_FASTCALL zend_undefined_index_write(HashTable *ht,
 	return retval;
 }
 
+static zval *zend_find_similar_entry(const HashTable *ht, const char *lcname, size_t lcname_len)
+{
+	if (lcname_len < 3) {
+		return NULL;
+	}
+
+	size_t threshold = lcname_len >= 8 ? 2 : 1;
+	zend_long best_dist = threshold + 1;
+	zval *best = NULL;
+
+	ZEND_HASH_MAP_FOREACH_STR_KEY_VAL(ht, zend_string *key, zval *val) {
+		if (!key || ZSTR_VAL(key)[0] == '\0' || Z_TYPE_P(val) == IS_ALIAS_PTR) {
+			continue;
+		}
+		if (ZSTR_LEN(key) > lcname_len + threshold || lcname_len > ZSTR_LEN(key) + threshold) {
+			continue;
+		}
+		zend_long dist = zend_levenshtein(lcname, lcname_len, ZSTR_VAL(key), ZSTR_LEN(key), 1, 1, 1);
+		if (dist > 0 && dist < best_dist) {
+			best_dist = dist;
+			best = val;
+		}
+	} ZEND_HASH_FOREACH_END();
+
+	return best;
+}
+
+zend_string *zend_find_similar_function(const char *lcname, size_t lcname_len)
+{
+	const zval *zv = zend_find_similar_entry(EG(function_table), lcname, lcname_len);
+	return zv ? Z_FUNC_P(zv)->common.function_name : NULL;
+}
+
+zend_string *zend_find_similar_class(const zend_string *class_name)
+{
+	zend_string *lc_name = zend_string_alloc(ZSTR_LEN(class_name), 0);
+	zend_str_tolower_copy(ZSTR_VAL(lc_name), ZSTR_VAL(class_name), ZSTR_LEN(class_name));
+	const zval *zv = zend_find_similar_entry(EG(class_table), ZSTR_VAL(lc_name), ZSTR_LEN(lc_name));
+	zend_string_release(lc_name);
+	return zv ? Z_CE_P(zv)->name : NULL;
+}
+
+static zend_string *zend_find_similar_method(const zend_class_entry *ce, const zend_string *method)
+{
+	zend_string *lc_method = zend_string_alloc(ZSTR_LEN(method), 0);
+	zend_str_tolower_copy(ZSTR_VAL(lc_method), ZSTR_VAL(method), ZSTR_LEN(method));
+	const zval *zv = zend_find_similar_entry(&ce->function_table, ZSTR_VAL(lc_method), ZSTR_LEN(lc_method));
+	zend_string_release(lc_method);
+	return zv ? Z_FUNC_P(zv)->common.function_name : NULL;
+}
+
 ZEND_API zend_never_inline ZEND_COLD void ZEND_FASTCALL zend_undefined_method(const zend_class_entry *ce, const zend_string *method)
 {
-	zend_throw_error(NULL, "Call to undefined method %s::%s()", ZSTR_VAL(ce->name), ZSTR_VAL(method));
+	zend_string *suggestion = zend_find_similar_method(ce, method);
+	if (suggestion) {
+		zend_throw_error(NULL, "Call to undefined method %s::%s() (did you mean %s?)", ZSTR_VAL(ce->name), ZSTR_VAL(method), ZSTR_VAL(suggestion));
+	} else {
+		zend_throw_error(NULL, "Call to undefined method %s::%s()", ZSTR_VAL(ce->name), ZSTR_VAL(method));
+	}
+}
+
+/* op2 is followed by the lowercased name and, for INIT_NS_FCALL_BY_NAME, the global fallback */
+ZEND_API zend_never_inline ZEND_COLD void ZEND_FASTCALL zend_undefined_function_error(const zend_op *opline)
+{
+	const zval *function_name = RT_CONSTANT(opline, opline->op2);
+	zend_string *suggestion = zend_find_similar_function(Z_STRVAL_P(function_name + 1), Z_STRLEN_P(function_name + 1));
+	if (!suggestion && opline->opcode == ZEND_INIT_NS_FCALL_BY_NAME) {
+		suggestion = zend_find_similar_function(Z_STRVAL_P(function_name + 2), Z_STRLEN_P(function_name + 2));
+	}
+	if (suggestion) {
+		zend_throw_error(NULL, "Call to undefined function %s() (did you mean %s?)", Z_STRVAL_P(function_name), ZSTR_VAL(suggestion));
+	} else {
+		zend_throw_error(NULL, "Call to undefined function %s()", Z_STRVAL_P(function_name));
+	}
 }
 
 static zend_never_inline ZEND_COLD void ZEND_FASTCALL zend_invalid_method_call(const zval *object, const zval *function_name)
@@ -5185,7 +5256,19 @@ static zend_never_inline zend_execute_data *zend_init_dynamic_call_string(zend_s
 	} else {
 		fbc = zend_fetch_function(function);
 		if (UNEXPECTED(fbc == NULL)) {
-			zend_throw_error(NULL, "Call to undefined function %s()", ZSTR_VAL(function));
+			if (ZSTR_VAL(function)[0] == '\\') {
+				lcname = zend_string_alloc(ZSTR_LEN(function) - 1, 0);
+				zend_str_tolower_copy(ZSTR_VAL(lcname), ZSTR_VAL(function) + 1, ZSTR_LEN(function) - 1);
+			} else {
+				lcname = zend_string_tolower(function);
+			}
+			zend_string *suggestion = zend_find_similar_function(ZSTR_VAL(lcname), ZSTR_LEN(lcname));
+			if (suggestion) {
+				zend_throw_error(NULL, "Call to undefined function %s() (did you mean %s?)", ZSTR_VAL(function), ZSTR_VAL(suggestion));
+			} else {
+				zend_throw_error(NULL, "Call to undefined function %s()", ZSTR_VAL(function));
+			}
+			zend_string_release_ex(lcname, 0);
 			return NULL;
 		}
 		called_scope = NULL;

Zend/zend_execute.h

@@ -559,6 +559,9 @@ ZEND_API ZEND_ATTRIBUTE_DEPRECATED HashTable *zend_unfinished_execution_gc(zend_
 ZEND_API HashTable *zend_unfinished_execution_gc_ex(zend_execute_data *execute_data, zend_execute_data *call, zend_get_gc_buffer *gc_buffer, bool suspended_by_yield);
 ZEND_API zval* ZEND_FASTCALL zend_fetch_static_property(zend_execute_data *ex, int fetch_type);
 ZEND_API zend_never_inline ZEND_COLD void ZEND_FASTCALL zend_undefined_method(const zend_class_entry *ce, const zend_string *method);
+ZEND_API zend_never_inline ZEND_COLD void ZEND_FASTCALL zend_undefined_function_error(const zend_op *opline);
+zend_string *zend_find_similar_function(const char *lcname, size_t lcname_len);
+zend_string *zend_find_similar_class(const zend_string *class_name);
 ZEND_API zend_never_inline ZEND_COLD void ZEND_FASTCALL zend_non_static_method_call(const zend_function *fbc);
 
 ZEND_API void zend_frameless_observed_call(zend_execute_data *execute_data);

Zend/zend_execute_API.c

@@ -1752,12 +1752,15 @@ static ZEND_COLD void report_class_fetch_error(const zend_string *class_name, ui
 		return;
 	}
 
-	if ((fetch_type & ZEND_FETCH_CLASS_MASK) == ZEND_FETCH_CLASS_INTERFACE) {
-		zend_throw_or_error(fetch_type, NULL, "Interface \"%s\" not found", ZSTR_VAL(class_name));
-	} else if ((fetch_type & ZEND_FETCH_CLASS_MASK) == ZEND_FETCH_CLASS_TRAIT) {
-		zend_throw_or_error(fetch_type, NULL, "Trait \"%s\" not found", ZSTR_VAL(class_name));
+	uint32_t mask = fetch_type & ZEND_FETCH_CLASS_MASK;
+	const char *kind = mask == ZEND_FETCH_CLASS_INTERFACE ? "Interface"
+	                 : mask == ZEND_FETCH_CLASS_TRAIT     ? "Trait"
+	                 :                                      "Class";
+	zend_string *suggestion = zend_find_similar_class(class_name);
+	if (suggestion) {
+		zend_throw_or_error(fetch_type, NULL, "%s \"%s\" not found (did you mean \"%s\"?)", kind, ZSTR_VAL(class_name), ZSTR_VAL(suggestion));
 	} else {
-		zend_throw_or_error(fetch_type, NULL, "Class \"%s\" not found", ZSTR_VAL(class_name));
+		zend_throw_or_error(fetch_type, NULL, "%s \"%s\" not found", kind, ZSTR_VAL(class_name));
 	}
 }