From 6bec8adf160fb40ee1101fbbfe8d852bb61f72c7 Mon Sep 17 00:00:00 2001
From: Rob23oba <152706811+Rob23oba@users.noreply.github.com>
Date: Wed, 21 Jan 2026 21:38:29 +0100
Subject: [PATCH] fix: symbol name for native boxed declarations in the
 interpreter (#12095)

This PR fixes the procedure for finding the mangled symbol name of boxed
variants of native functions. Previously, the wrong symbol name has been
used for names ending in `_`: For example `test_` mangles to `l_test__`
but `test_._boxed` mangles to `l_test___00__boxed`, not
`l_test_____boxed` which the compiler would previously wrongly use.
This probably didn't affect anybody though since the failure condition
is pretty rare: the name of a native function that the interpreter tries
to execute would've had to end in `_`.
---
 src/Lean/Compiler/ModPkgExt.lean    |  6 +++---
 src/Lean/Compiler/NameMangling.lean | 14 +++++++++++++-
 src/library/ir_interpreter.cpp      | 14 ++++++++------
 tests/lean/run/mangling.lean        |  7 ++++++-
 4 files changed, 30 insertions(+), 11 deletions(-)

diff --git a/src/Lean/Compiler/ModPkgExt.lean b/src/Lean/Compiler/ModPkgExt.lean
index f96d5bbb74..29ede4dfc6 100644
--- a/src/Lean/Compiler/ModPkgExt.lean
+++ b/src/Lean/Compiler/ModPkgExt.lean
@@ -56,9 +56,9 @@ public def Environment.getModulePackageByIdx? (env : Environment) (idx : ModuleI
 Returns the standard base of the native symbol for the compiled constant {lean}`declName`.
 
 For many constants, this is the full symbol. However, initializers have an additional prefix
-(i.e., {lit}`_init_`) and boxed functions have an additional suffix (i.e., {lit}`___boxed`).
-Furthermore, some constants do not use this stem at all (e.g., {lit}`main` and definitions
-with {lit}`@[export]`).
+(i.e., {lit}`_init_`) and boxed functions have an additional suffix
+(see {name}`mkMangledBoxedName`). Furthermore, some constants do not use this stem at all
+(e.g., {lit}`main` and definitions with {lit}`@[export]`).
 -/
 @[export lean_get_symbol_stem]
 public def getSymbolStem (env : Environment) (declName : Name) : String :=
diff --git a/src/Lean/Compiler/NameMangling.lean b/src/Lean/Compiler/NameMangling.lean
index cac708aac9..d5ae148fe9 100644
--- a/src/Lean/Compiler/NameMangling.lean
+++ b/src/Lean/Compiler/NameMangling.lean
@@ -7,7 +7,7 @@ module
 
 prelude
 public import Lean.Setup
-import Init.Data.String.Termination
+import Init.Data.String.TakeDrop
 
 namespace String
 
@@ -133,6 +133,18 @@ def Name.mangleAux : Name → String
 public def Name.mangle (n : Name) (pre : String := "l_") : String :=
   pre ++ Name.mangleAux n
 
+/--
+Given `s = nm.mangle pre` for some `nm : Name` and `pre : String` with `nm != Name.anonymous`,
+returns `(mkBoxedName nm).mangle pre`. This is used in the interpreter to find names of boxed
+IR declarations.
+-/
+@[export lean_mk_mangled_boxed_name]
+public def mkMangledBoxedName (s : String) : String :=
+  if s.endsWith "__" then
+    s ++ "_00__boxed"
+  else
+    s ++ "___boxed"
+
 /--
 The mangled name of the name used to create the module initialization function.
 
diff --git a/src/library/ir_interpreter.cpp b/src/library/ir_interpreter.cpp
index 9766c2dd79..8a79a50e03 100644
--- a/src/library/ir_interpreter.cpp
+++ b/src/library/ir_interpreter.cpp
@@ -200,7 +200,6 @@ option_ref<decl> find_ir_decl_boxed(elab_environment const & env, name const & n
 extern "C" double lean_float_of_nat(lean_obj_arg a);
 extern "C" float lean_float32_of_nat(lean_obj_arg a);
 
-static string_ref * g_boxed_mangled_suffix = nullptr;
 static name * g_interpreter_prefer_native = nullptr;
 DEBUG_CODE(static name * g_interpreter_step = nullptr;)
 DEBUG_CODE(static name * g_interpreter_call = nullptr;)
@@ -216,6 +215,12 @@ string_ref get_symbol_stem(elab_environment const & env, name const & fn) {
     return string_ref(lean_get_symbol_stem(env.to_obj_arg(), fn.to_obj_arg()));
 }
 
+extern "C" obj_res lean_mk_mangled_boxed_name(obj_arg str);
+
+string_ref mk_mangled_boxed_name(string_ref const & str) {
+    return string_ref(lean_mk_mangled_boxed_name(str.to_obj_arg()));
+}
+
 extern "C" object * lean_ir_format_fn_body_head(object * b);
 std::string format_fn_body_head(fn_body const & b) {
     object_ref s(lean_ir_format_fn_body_head(b.to_obj_arg()));
@@ -843,7 +848,7 @@ private:
         symbol_cache_entry e_new { get_decl(fn), {nullptr, false} };
         if (m_prefer_native || decl_tag(e_new.m_decl) == decl_kind::Extern || has_init_attribute(m_env, fn)) {
             string_ref mangled = get_symbol_stem(m_env, fn);
-            string_ref boxed_mangled(string_append(mangled.to_obj_arg(), g_boxed_mangled_suffix->raw()));
+            string_ref boxed_mangled = mk_mangled_boxed_name(mangled);
             // check for boxed version first
             if (void *p_boxed = lookup_symbol_in_cur_exe(boxed_mangled.data())) {
                 e_new.m_native.m_addr = p_boxed;
@@ -965,7 +970,7 @@ private:
         } else {
             if (decl_tag(e.m_decl) == decl_kind::Extern) {
                 string_ref mangled = get_symbol_stem(m_env, fn);
-                string_ref boxed_mangled(string_append(mangled.to_obj_arg(), g_boxed_mangled_suffix->raw()));
+                string_ref boxed_mangled = mk_mangled_boxed_name(mangled);
                 throw exception(sstream() << "Could not find native implementation of external declaration '" << fn
                                           << "' (symbols '" << boxed_mangled.data() << "' or '" << mangled.data() << "').\n"
                                           << "For declarations from `Init`, `Std`, or `Lean`, you need to set `supportInterpreter := true` "
@@ -1212,8 +1217,6 @@ extern "C" LEAN_EXPORT object * lean_run_init(object * env, object * opts, objec
 }
 
 void initialize_ir_interpreter() {
-    ir::g_boxed_mangled_suffix = new string_ref("___boxed");
-    mark_persistent(ir::g_boxed_mangled_suffix->raw());
     ir::g_interpreter_prefer_native = new name({"interpreter", "prefer_native"});
     ir::g_init_globals = new name_hash_map<object *>();
     register_bool_option(*ir::g_interpreter_prefer_native, LEAN_DEFAULT_INTERPRETER_PREFER_NATIVE, "(interpreter) whether to use precompiled code where available");
@@ -1236,6 +1239,5 @@ void finalize_ir_interpreter() {
     });
     delete ir::g_init_globals;
     delete ir::g_interpreter_prefer_native;
-    delete ir::g_boxed_mangled_suffix;
 }
 }
diff --git a/tests/lean/run/mangling.lean b/tests/lean/run/mangling.lean
index b1286eb8d0..3ca056dd49 100644
--- a/tests/lean/run/mangling.lean
+++ b/tests/lean/run/mangling.lean
@@ -1,15 +1,20 @@
 module
+import Lean.Compiler.IR.CompilerM
 import Lean.Compiler.NameMangling
 
 /-!
 # Test behavior of name mangling
 -/
 
-def checkMangle (n : Lean.Name) (s : String) : IO Unit := do
+open Lean IR ExplicitBoxing
+def checkMangle (n : Name) (s : String) : IO Unit := do
   if n.mangle "" ≠ s then
     throw <| .userError s!"failed: {n} mangles to {n.mangle ""} but expected {s}"
   if .demangle s ≠ n then
     throw <| .userError s!"failed: {s} demangles to {Lean.Name.demangle s} but expected {n}"
+  if n ≠ .anonymous ∧ mkMangledBoxedName s ≠ (mkBoxedName n).mangle "" then
+    throw <| .userError s!"failed: {mkBoxedName n} mangles to {(mkBoxedName n).mangle ""} but \
+      mkMangledBoxedName produced {mkMangledBoxedName s}"
 
 /-!
 Mangling simple identifiers with optional number components and preceding underscores.