From d4f4c7d652a3647f0aa616f973a52f35d8b49f06 Mon Sep 17 00:00:00 2001
From: Charlie Gordon <github@chqrlie.org>
Date: Fri, 17 Apr 2026 23:05:13 +0200
Subject: [PATCH] C-Generator: fix nested function type output

* fix generated code for type definitions involving function that take
  function pointer arguments
* fix and extend bogus test (!)
---
 generator/c/c_generator.c2           | 59 +++++++++++++---------------
 test/functions/func_param_nested.c2t | 30 +++++++++++++-
 2 files changed, 57 insertions(+), 32 deletions(-)

diff --git a/generator/c/c_generator.c2 b/generator/c/c_generator.c2
index d4b65c1a8..fed8f063d 100644
--- a/generator/c/c_generator.c2
+++ b/generator/c/c_generator.c2
@@ -461,6 +461,30 @@ fn void Generator.emitStruct(Generator* gen, string_buffer.Buf* out, Decl* d, u3
     }
 }
 
+fn void Generator.emitFunctionParam(Generator* gen, string_buffer.Buf* out, QualType qt, u32 name_idx, u32 arg_num) {
+    char[16] temp;
+    const char* name;
+    if (name_idx) {
+        name = gen.idx2name(name_idx);
+    } else {
+        // some compilers do not accept unnamed arguments in function definitions
+        snprintf(temp, elemsof(temp), "_arg%d", arg_num);
+        name = temp;
+    }
+    if (qt.isFunction()) {
+        FunctionType* ft = qt.getFunctionType();
+        FunctionDecl* fd = ft.getDecl();
+        if (fd.isParam()) {
+            gen.gen_member_type_func(fd, out, name);
+            return;
+        }
+        // TODO: when to we get here?
+    }
+    gen.emitTypePre(out, qt);
+    out.space();
+    out.add(name);
+}
+
 fn void Generator.emitFunctionType(Generator* gen, string_buffer.Buf* out, Decl* d) {
     FunctionTypeDecl* ftd = (FunctionTypeDecl*)d;
     FunctionDecl* fd = ftd.getDecl();
@@ -474,15 +498,9 @@ fn void Generator.emitFunctionType(Generator* gen, string_buffer.Buf* out, Decl*
     u32 num_params = fd.getNumParams();
     VarDecl** params = fd.getParams();
     for (u32 i=0; i<num_params; i++) {
-        Decl* arg = (Decl*)params[i];
         if (i != 0) out.add(", ");
-        gen.emitTypePre(out, arg.getType());
-        out.space();
-        if (arg.getNameIdx()) {
-            gen.emitName(out, arg);
-        } else {
-            out.print("_arg%d", i);
-        }
+        Decl* arg = (Decl*)params[i];
+        gen.emitFunctionParam(out, arg.getType(), arg.getNameIdx(), i);
     }
     if (fd.isVariadic()) {
         if (num_params) out.add(", ");
@@ -900,30 +918,9 @@ fn void Generator.emitFuncParams(Generator* gen, FunctionDecl* fd, string_buffer
 
     VarDecl** params = fd.getParams();
     for (u32 i=0; i<num_params; i++) {
-        Decl* argx = (Decl*)params[i];
         if (i != 0) out.add(", ");
-        char[8] temp;
-        const char* name;
-        u32 name_idx = argx.getNameIdx();
-        if (name_idx) {
-            name = gen.idx2name(name_idx);
-        } else {
-            snprintf(temp, elemsof(temp), "_arg%d", i);
-            name = temp;
-        }
-        QualType qt = argx.getType();
-        if (qt.isFunction()) {
-            FunctionType* ft = qt.getFunctionType();
-            FunctionDecl* fd2 = ft.getDecl();
-            if (fd2.isParam()) {
-                gen.gen_member_type_func(fd2, out, name);
-                continue;
-            }
-        }
-
-        gen.emitTypePre(out, qt);
-        out.space();
-        out.add(name);
+        Decl* arg = (Decl*)params[i];
+        gen.emitFunctionParam(out, arg.getType(), arg.getNameIdx(), i);
     }
     if (fd.isVariadic()) {
         if (num_params) out.add(", ");
diff --git a/test/functions/func_param_nested.c2t b/test/functions/func_param_nested.c2t
index bf03ede62..8e29bc61c 100644
--- a/test/functions/func_param_nested.c2t
+++ b/test/functions/func_param_nested.c2t
@@ -5,6 +5,11 @@
 // @file{file1}
 module test;
 
+fn void foo() { foo1(foo); }
+fn void foo1(fn void()) { foo2(foo1); }
+fn void foo2(fn void(fn void())) { foo3(foo2); }
+fn void foo3(fn void(fn void(fn void()))) {}
+
 type Cb1 fn void(void*, fn bool(i32, i32), i32);
 type Cb2 fn bool(i32, i32);
 
@@ -30,16 +35,39 @@ fn void test2() {
     test1(nil, nil, nil, 10);
 }
 // @expect{atleast, cgen/build.c}
-typedef void (*test_Cb1)(void* _arg0,  _arg1, int _arg2);
+typedef void (*test_Cb1)(void* _arg0, bool (*_arg1)(int _arg0, int _arg1), int _arg2);
 typedef bool (*test_Cb2)(int _arg0, int _arg1);
 
 static void test_callback1(void* arg, bool (*_arg1)(int _arg0, int _arg1), int a);
 static test_Cb1 test_cb1 = test_callback1;
 static bool test_callback2(int a, int b);
 static test_Cb2 test_cb2 = test_callback2;
+static void test_foo(void);
+static void test_foo1(void (*_arg0)(void));
+static void test_foo2(void (*_arg0)(void (*_arg0)(void)));
+static void test_foo3(void (*_arg0)(void (*_arg0)(void (*_arg0)(void))));
 static void test_test1(void* arg, void (*cb)(void* arg, bool (*_arg1)(int _arg0, int _arg1), int a), bool (*inner)(int _arg0, int _arg1), int a);
 static void test_test2(void);
 
+static void test_foo(void)
+{
+   test_foo1(test_foo);
+}
+
+static void test_foo1(void (*_arg0)(void))
+{
+   test_foo2(test_foo1);
+}
+
+static void test_foo2(void (*_arg0)(void (*_arg0)(void)))
+{
+   test_foo3(test_foo2);
+}
+
+static void test_foo3(void (*_arg0)(void (*_arg0)(void (*_arg0)(void))))
+{
+}
+
 static void test_callback1(void* arg, bool (*_arg1)(int _arg0, int _arg1), int a)
 {
 }