From f3cd815c77ff4d690762b53aed85c1f77e3df73c Mon Sep 17 00:00:00 2001
From: nyash-codex <codex@nyash.local>
Date: Mon, 17 Nov 2025 18:23:00 +0900
Subject: [PATCH] feat(parsercontrol): add shallow recursion guards to
 ParserControlBox (if/loop/break/continue/block)

---
 .../parser/stmt/parser_control_box.hako       | 49 +++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/lang/src/compiler/parser/stmt/parser_control_box.hako b/lang/src/compiler/parser/stmt/parser_control_box.hako
index 91fca714..3e5242d6 100644
--- a/lang/src/compiler/parser/stmt/parser_control_box.hako
+++ b/lang/src/compiler/parser/stmt/parser_control_box.hako
@@ -7,6 +7,16 @@ using sh_core as StringHelpers  // Required: using chain resolution not implemen
 static box ParserControlBox {
   // Parse: if (cond) { ... } else { ... }
   parse_if(src, i, stmt_start, ctx) {
+    // Shallow recursion guard for Stage‑B / selfhost: protect parse_if from
+    // accidental self-recursion via malformed input or control flow bugs.
+    {
+      local depth = env.get("HAKO_STAGEB_IF_DEPTH")
+      if depth != null && ("" + depth) != "0" {
+        print("[stageb/recursion] ParserControlBox.parse_if recursion detected")
+        return "{\"type\":\"If\",\"cond\":{\"type\":\"Bool\",\"value\":false},\"then\":[]}"
+      }
+      env.set("HAKO_STAGEB_IF_DEPTH", "1")
+    }
     local j = i + 2  // skip "if"
     j = ctx.skip_ws(src, j)
     local paren = 0
@@ -42,6 +52,7 @@ static box ParserControlBox {
     }
     ctx.gpos_set(j)
 
+    env.set("HAKO_STAGEB_IF_DEPTH", "0")
     if else_json == null {
       return "{\"type\":\"If\",\"cond\":" + cond + ",\"then\":" + then_json + "}"
     } else {
@@ -52,6 +63,16 @@ static box ParserControlBox {
   // Parse: loop(cond) { ... }
   // Dev tracing: set HAKO_PARSER_TRACE_LOOP=1 to enable debug prints
   parse_loop(src, i, stmt_start, ctx) {
+    // Shallow recursion guard for parse_loop
+    {
+      local depth = env.get("HAKO_STAGEB_LOOP_DEPTH")
+      if depth != null && ("" + depth) != "0" {
+        print("[stageb/recursion] ParserControlBox.parse_loop recursion detected")
+        return "{\"type\":\"Loop\",\"cond\":{\"type\":\"Bool\",\"value\":false},\"body\":[]}"
+      }
+      env.set("HAKO_STAGEB_LOOP_DEPTH", "1")
+    }
+
     local trace = 0  // dev-only (disabled in Stage-B runtime: no env API here)
     local j = i + 4  // skip "loop"
     j = ctx.skip_ws(src, j)
@@ -133,11 +154,20 @@ static box ParserControlBox {
       if j < src.length() { j = j + 1 } else { j = src.length() }
     }
     ctx.gpos_set(j)
+    env.set("HAKO_STAGEB_LOOP_DEPTH", "0")
     return "{\"type\":\"Loop\",\"cond\":" + cond + ",\"body\":" + body_json + "}"
   }
 
   // Parse: break → {type:"Break"} (Stage-3) or no-op
   parse_break(src, i, stmt_start, ctx) {
+    {
+      local depth = env.get("HAKO_STAGEB_BREAK_DEPTH")
+      if depth != null && ("" + depth) != "0" {
+        print("[stageb/recursion] ParserControlBox.parse_break recursion detected")
+        return "{\"type\":\"Break\"}"
+      }
+      env.set("HAKO_STAGEB_BREAK_DEPTH", "1")
+    }
     local j = i + 5  // skip "break"
 
     if ctx.stage3_enabled() == 1 {
@@ -153,11 +183,20 @@ static box ParserControlBox {
       if j < src.length() { j = j + 1 } else { j = src.length() }
     }
     ctx.gpos_set(j)
+    env.set("HAKO_STAGEB_BREAK_DEPTH", "0")
     return "{\"type\":\"Expr\",\"expr\":{\"type\":\"Int\",\"value\":0}}"
   }
 
   // Parse: continue → {type:"Continue"} (Stage-3) or no-op
   parse_continue(src, i, stmt_start, ctx) {
+    {
+      local depth = env.get("HAKO_STAGEB_CONTINUE_DEPTH")
+      if depth != null && ("" + depth) != "0" {
+        print("[stageb/recursion] ParserControlBox.parse_continue recursion detected")
+        return "{\"type\":\"Continue\"}"
+      }
+      env.set("HAKO_STAGEB_CONTINUE_DEPTH", "1")
+    }
     local j = i + 8  // skip "continue"
 
     if ctx.stage3_enabled() == 1 {
@@ -173,11 +212,20 @@ static box ParserControlBox {
       if j < src.length() { j = j + 1 } else { j = src.length() }
     }
     ctx.gpos_set(j)
+    env.set("HAKO_STAGEB_CONTINUE_DEPTH", "0")
     return "{\"type\":\"Expr\",\"expr\":{\"type\":\"Int\",\"value\":0}}"
   }
 
   // Parse: { stmt1; stmt2; ... }
   parse_block(src, i, ctx) {
+    {
+      local depth = env.get("HAKO_STAGEB_BLOCK_DEPTH")
+      if depth != null && ("" + depth) != "0" {
+        print("[stageb/recursion] ParserControlBox.parse_block recursion detected")
+        return "[]@" + ctx.i2s(i)
+      }
+      env.set("HAKO_STAGEB_BLOCK_DEPTH", "1")
+    }
     local j = ctx.skip_ws(src, i)
     if src.substring(j, j+1) != "{" { return "[]@" + ctx.i2s(j) }
     j = j + 1
@@ -231,6 +279,7 @@ static box ParserControlBox {
     }
 
     body = body + "]"
+    env.set("HAKO_STAGEB_BLOCK_DEPTH", "0")
     return body + "@" + ctx.i2s(j)
   }
 }