fix(parser): 支持判断 if/else 终止的 switch case

src/Parser/SwitchTrait.php

@@ -87,12 +87,8 @@ trait SwitchTrait
                 $stmts = $stmts[0]->stmts;
             }
             $lastExpr = end($stmts);
-            if (!$this->isReturnExpr($lastExpr)
-                and !$this->isExitExpr($lastExpr)
-                and !$this->isBreakExpr($lastExpr)
-                and !$this->isThrowExpr($lastExpr)
-            ) {
-                $this->fatalError($case, 'switch case must end with return/break/exit/throw, ' . $lastExpr->getType() . ' given');
+            if (!$this->caseBodyTerminates($stmts)) {
+                $this->fatalError($case, 'switch case must end with return/break/exit/throw or a fully terminating if/else, ' . $lastExpr->getType() . ' given');
             }
             $target = count($caseGroups);
             if ($hasDefault) {
@@ -162,4 +158,66 @@ trait SwitchTrait
         return $var_def . $code;
     }
 
+    /**
+     * 判断一组语句是否总是终止（所有控制流路径都以 return/break/continue/exit/throw 结束）。
+     *
+     * 在 switch 降级为 if 链时，每个 case 必须是终止的，否则原本的穿透（fall-through）
+     * 语义无法在「每个 case 独立成 if 块」的实现中表达，会产生错误行为。
+     */
+    private function caseBodyTerminates(array $stmts): bool
+    {
+        if (empty($stmts)) {
+            return false;
+        }
+
+        return $this->stmtAlwaysTerminates(end($stmts));
+    }
+
+    /**
+     * 判断单条语句是否总是终止控制流。
+     */
+    private function stmtAlwaysTerminates(Node $stmt): bool
+    {
+        if ($stmt instanceof Node\Stmt\Return_
+            or $stmt instanceof Node\Stmt\Break_
+            or $stmt instanceof Node\Stmt\Continue_
+            or $stmt instanceof Node\Expr\Exit_
+            or $stmt instanceof Node\Expr\Throw_
+        ) {
+            return true;
+        }
+
+        // Stmt_Expression 包裹的 exit/die/throw
+        if ($stmt instanceof Node\Stmt\Expression) {
+            $expr = $stmt->expr;
+            if ($expr instanceof Node\Expr\Exit_ or $expr instanceof Node\Expr\Throw_) {
+                return true;
+            }
+        }
+
+        if ($stmt instanceof Node\Stmt\Block) {
+            return $this->caseBodyTerminates($stmt->stmts);
+        }
+
+        if ($stmt instanceof Node\Stmt\If_) {
+            // 必须有 else 分支覆盖所有路径，且 if / 每个 elseif / else 分支都终止
+            if ($stmt->else === null) {
+                return false;
+            }
+            if (!$this->caseBodyTerminates($stmt->stmts)) {
+                return false;
+            }
+            foreach ($stmt->elseifs as $elseif) {
+                if (!$this->caseBodyTerminates($elseif->stmts)) {
+                    return false;
+                }
+            }
+
+            return $this->caseBodyTerminates($stmt->else->stmts);
+        }
+
+        // 循环、try/catch、嵌套 switch 等结构保守认为不终止
+        return false;
+    }
+
 }

tests/compiler/switch/default-before-matching-case-ifelse.phpt

@@ -0,0 +1,20 @@
+--TEST--
+default placed before a later matching case, both using if/else return
+--FILE--
+<?php
+function main()
+{
+    $a = 2;
+    switch ($a)
+    {
+        default:
+            if (true) { echo "D\n"; return; } else { echo "De\n"; return; }
+        case 1:
+            if (true) { echo "1\n"; return; } else { echo "1e\n"; return; }
+        case 2:
+            if (true) { echo "2\n"; return; } else { echo "2e\n"; return; }
+    }
+}
+?>
+--EXPECT--
+2

tests/compiler/switch/if-else-return-001.phpt

@@ -0,0 +1,36 @@
+--TEST--
+switch case ending with if/else where both branches return (regression)
+--FILE--
+<?php
+function main()
+{
+    $a = 1;
+    switch ($a)
+    {
+        case 0:
+            if (true)
+            {
+                var_dump('a');
+                return;
+            }
+            else
+            {
+                var_dump('b');
+                return;
+            }
+        default:
+            if (true)
+            {
+                var_dump('c');
+                return;
+            }
+            else
+            {
+                var_dump('d');
+                return;
+            }
+    }
+}
+?>
+--EXPECT--
+string(1) "c"

tests/compiler/switch/if-else-return-002.phpt

@@ -0,0 +1,36 @@
+--TEST--
+switch case matching with if/else return, default not taken
+--FILE--
+<?php
+function main()
+{
+    $a = 0;
+    switch ($a)
+    {
+        case 0:
+            if (true)
+            {
+                var_dump('a');
+                return;
+            }
+            else
+            {
+                var_dump('b');
+                return;
+            }
+        default:
+            if (true)
+            {
+                var_dump('c');
+                return;
+            }
+            else
+            {
+                var_dump('d');
+                return;
+            }
+    }
+}
+?>
+--EXPECT--
+string(1) "a"

tests/compiler/switch/if-else-return-no-default.phpt

@@ -0,0 +1,19 @@
+--TEST--
+switch without default, if/else return case, non-matching value falls through
+--FILE--
+<?php
+function main()
+{
+    $a = 9;
+    switch ($a)
+    {
+        case 1:
+            if (true) { echo "1\n"; return; } else { echo "1e\n"; return; }
+        case 2:
+            if (true) { echo "2\n"; return; } else { echo "2e\n"; return; }
+    }
+    echo "after\n";
+}
+?>
+--EXPECT--
+after

tests/compiler/switch/if-elseif-else-return.phpt

@@ -0,0 +1,20 @@
+--TEST--
+switch case ending with if/elseif/else where every branch returns
+--FILE--
+<?php
+function main()
+{
+    $a = 2;
+    switch ($a)
+    {
+        case 1:
+            if (true) { echo "1\n"; return; } else { echo "1e\n"; return; }
+        case 2:
+            if ($a === 2) { echo "two\n"; return; } elseif ($a === 3) { echo "three\n"; return; } else { echo "other\n"; return; }
+        default:
+            if (true) { echo "D\n"; return; } else { echo "De\n"; return; }
+    }
+}
+?>
+--EXPECT--
+two

tests/compiler/switch/mixed-return-ifelse.phpt

@@ -0,0 +1,20 @@
+--TEST--
+switch mixing plain return case with if/else return case
+--FILE--
+<?php
+function main()
+{
+    $a = 2;
+    switch ($a)
+    {
+        case 1:
+            echo "1\n"; return;
+        case 2:
+            if (true) { echo "2if\n"; return; } else { echo "2else\n"; return; }
+        default:
+            echo "D\n"; return;
+    }
+}
+?>
+--EXPECT--
+2if

tests/compiler/switch/nested-if-else-return.phpt

@@ -0,0 +1,22 @@
+--TEST--
+switch case ending with nested if/else where all paths return
+--FILE--
+<?php
+function main()
+{
+    $a = 5;
+    switch ($a)
+    {
+        case 5:
+            if (true) {
+                if ($a > 0) { echo "inner\n"; return; } else { echo "inner-else\n"; return; }
+            } else {
+                echo "outer-else\n"; return;
+            }
+        default:
+            if (true) { echo "D\n"; return; } else { echo "De\n"; return; }
+    }
+}
+?>
+--EXPECT--
+inner

tests/compiler/switch/shared-case-if-else-return.phpt

@@ -0,0 +1,19 @@
+--TEST--
+multiple case labels sharing an if/else return body
+--FILE--
+<?php
+function main()
+{
+    $a = 1;
+    switch ($a)
+    {
+        case 1:
+        case 2:
+            if (true) { echo "one-or-two\n"; return; } else { echo "never\n"; return; }
+        default:
+            if (true) { echo "D\n"; return; } else { echo "De\n"; return; }
+    }
+}
+?>
+--EXPECT--
+one-or-two

tests/compiler/switch/string-if-else-return.phpt

@@ -0,0 +1,20 @@
+--TEST--
+string switch with if/else return cases and default
+--FILE--
+<?php
+function main()
+{
+    $v = 'x';
+    switch ($v)
+    {
+        case 'a':
+            if (true) { echo "A\n"; return; } else { echo "a\n"; return; }
+        case 'b':
+            if (true) { echo "B\n"; return; } else { echo "b\n"; return; }
+        default:
+            if (true) { echo "DEFAULT\n"; return; } else { echo "default\n"; return; }
+    }
+}
+?>
+--EXPECT--
+DEFAULT