GDScript regression: Compiler bug: unresolved assign

[akien-mga]

Tested versions

• Reproducible in 4.3.dev6 and later, including latest master (f6c7b00) and PR GDScript: Fix common mismatched external parser errors (reverted) #94617
• Not reproducible in 4.3.dev5 and earlier, or 4.2.2.stable
• Bisected to GDScript: Fix uninitialized local variables not being reset #89990, CC @dalexeev

System information

Fedora Linux 40 (KDE Plasma) - Wayland - Vulkan (Forward+) - dedicated AMD Radeon RX 7600M XT (RADV NAVI33) - AMD Ryzen 7 7840HS w/ Radeon 780M Graphics (16 Threads)

Issue description

Moving one of the two regressions identified in #94244 to its own issue, as #94617 fixes the other one and will solve the original report from #94244.

The MRP (not really minimal, it's an empty project with Zylann's hterrain plugin installed), triggers the following error since #89990:

ERROR: Compiler bug: unresolved assign.
   at: write_assign_with_conversion (modules/gdscript/gdscript_byte_codegen.cpp:919)

This is still reproducible after #94617 too.

Steps to reproduce

• Open MRP, see console output

Minimal reproduction project (MRP)

Reproduction project (empty project with Zylann hterrain installed):
hterraintest.zip

[akien-mga]

I put a breakpoint to identify which scripts triggers the error, I'll see if I can make a smaller MRP:

Thread 1 "godot-git" hit Breakpoint 1, GDScriptByteCodeGenerator::write_assign_with_conversion (this=0x28adeae0, p_target=..., p_source=...) at ./modules/gdscript/gdscript_byte_codegen.cpp:919
919                             ERR_PRINT("Compiler bug: unresolved assign.");
Missing separate debuginfos, use: dnf debuginfo-install alsa-lib-1.2.12-1.fc40.x86_64 bzip2-libs-1.0.8-18.fc40.x86_64 dbus-libs-1.14.10-3.fc40.x86_64 elfutils-libelf-0.191-4.fc40.x86_64 expat-2.6.2-1.fc40.x86_64 flac-libs-1.4.3-4.fc40.x86_64 fontconfig-2.15.0-6.fc40.x86_64 freetype-2.13.2-5.fc40.x86_64 glib2-2.80.3-1.fc40.x86_64 glibc-2.39-17.fc40.x86_64 graphite2-1.3.14-15.fc40.x86_64 gsm-1.0.22-6.fc40.x86_64 harfbuzz-8.5.0-1.fc40.x86_64 lame-libs-3.100-17.fc40.x86_64 libX11-1.8.9-1.fc40.x86_64 libX11-xcb-1.8.9-1.fc40.x86_64 libXau-1.0.11-6.fc40.x86_64 libXcursor-1.2.1-7.fc40.x86_64 libXext-1.3.6-1.fc40.x86_64 libXfixes-6.0.1-3.fc40.x86_64 libXi-1.8.1-5.fc40.x86_64 libXinerama-1.1.5-6.fc40.x86_64 libXrender-0.9.11-6.fc40.x86_64 libbrotli-1.1.0-3.fc40.x86_64 libcap-2.69-8.fc40.x86_64 libdrm-2.4.121-1.fc40.x86_64 libffi-3.4.4-7.fc40.x86_64 libgcc-14.1.1-7.fc40.x86_64 libpng-1.6.40-3.fc40.x86_64 libsndfile-1.2.2-2.fc40.x86_64 libstdc++-14.1.1-7.fc40.x86_64 libvorbis-1.3.7-10.fc40.x86_64 libxcb-1.17.0-1.fc40.x86_64 libxkbcommon-1.6.0-2.fc40.x86_64 libxml2-2.12.8-1.fc40.x86_64 libzstd-1.5.6-1.fc40.x86_64 mesa-vulkan-drivers-24.1.4-2.fc40.x86_64 mpg123-libs-1.31.3-4.fc40.x86_64 ncurses-libs-6.4-12.20240127.fc40.x86_64 opus-1.5.1-1.fc40.x86_64 pcre2-10.44-1.fc40.x86_64 systemd-libs-255.8-1.fc40.x86_64 xz-libs-5.4.6-3.fc40.x86_64 zlib-ng-compat-2.1.7-1.fc40.x86_64
(gdb) bt
#0  GDScriptByteCodeGenerator::write_assign_with_conversion (this=0x28adeae0, p_target=..., p_source=...) at ./modules/gdscript/gdscript_byte_codegen.cpp:919
#1  0x00000000066ebdba in GDScriptCompiler::_parse_block (this=0x7fffffffa360, codegen=..., p_block=0x28b49c20, p_add_locals=false, p_clear_locals=true) at ./modules/gdscript/gdscript_compiler.cpp:2164
#2  0x00000000066eb5e5 in GDScriptCompiler::_parse_block (this=0x7fffffffa360, codegen=..., p_block=0x28b4a500, p_add_locals=false, p_clear_locals=true) at ./modules/gdscript/gdscript_compiler.cpp:2050
#3  0x00000000066eb5e5 in GDScriptCompiler::_parse_block (this=0x7fffffffa360, codegen=..., p_block=0x279c6460, p_add_locals=true, p_clear_locals=true) at ./modules/gdscript/gdscript_compiler.cpp:2050
#4  0x00000000066eb2dd in GDScriptCompiler::_parse_block (this=0x7fffffffa360, codegen=..., p_block=0x28b32b40, p_add_locals=true, p_clear_locals=false) at ./modules/gdscript/gdscript_compiler.cpp:2015
#5  0x00000000066ed0c2 in GDScriptCompiler::_parse_function (this=0x7fffffffa360, r_error=@0x7fffffffa034: OK, p_script=0x2763d9b0, p_class=0x2875d710, p_func=0x2861c4e0, p_for_ready=false, p_for_lambda=false)
    at ./modules/gdscript/gdscript_compiler.cpp:2384
#6  0x00000000066f04e5 in GDScriptCompiler::_compile_class (this=0x7fffffffa360, p_script=0x2763d9b0, p_class=0x2875d710, p_keep_state=true) at ./modules/gdscript/gdscript_compiler.cpp:2905
#7  0x00000000066f1e09 in GDScriptCompiler::compile (this=0x7fffffffa360, p_parser=0x7fffffffa450, p_script=0x2763d9b0, p_keep_state=true) at ./modules/gdscript/gdscript_compiler.cpp:3231
#8  0x00000000066a2957 in GDScript::reload (this=0x2763d9b0, p_keep_state=true) at ./modules/gdscript/gdscript.cpp:839
#9  0x00000000066de825 in GDScriptCache::get_full_script (p_path=..., r_error=@0x7fffffffaf9c: OK, p_owner=..., p_update_from_disk=false) at ./modules/gdscript/gdscript_cache.cpp:359
#10 0x00000000066deae0 in GDScriptCache::finish_compiling (p_owner=...) at ./modules/gdscript/gdscript_cache.cpp:399
#11 0x00000000066f1ef5 in GDScriptCompiler::compile (this=0x7fffffffb2a0, p_parser=0x7fffffffb390, p_script=0x264ae720, p_keep_state=true) at ./modules/gdscript/gdscript_compiler.cpp:3246
#12 0x00000000066a2957 in GDScript::reload (this=0x264ae720, p_keep_state=true) at ./modules/gdscript/gdscript.cpp:839
#13 0x00000000066de825 in GDScriptCache::get_full_script (p_path=..., r_error=@0x7fffffffbf04: OK, p_owner=..., p_update_from_disk=true) at ./modules/gdscript/gdscript_cache.cpp:359
#14 0x00000000066af4aa in ResourceFormatLoaderGDScript::load (this=0xbac5340, p_path=..., p_original_path=..., r_error=0x7fffffffc0b4, p_use_sub_threads=false, r_progress=0x7fffffffc270, 
    p_cache_mode=ResourceFormatLoader::CACHE_MODE_IGNORE) at ./modules/gdscript/gdscript.cpp:2932
#15 0x000000000a76f64f in ResourceLoader::_load (p_path=..., p_original_path=..., p_type_hint=..., p_cache_mode=ResourceFormatLoader::CACHE_MODE_IGNORE, r_error=0x7fffffffc0b4, p_use_sub_threads=false, 
    r_progress=0x7fffffffc270) at ./core/io/resource_loader.cpp:269
#16 0x000000000a76fcec in ResourceLoader::_thread_load_function (p_userdata=0x7fffffffc230) at ./core/io/resource_loader.cpp:323
#17 0x000000000a770bce in ResourceLoader::_load_start (p_path=..., p_type_hint=..., p_thread_mode=ResourceLoader::LOAD_THREAD_FROM_CURRENT, p_cache_mode=ResourceFormatLoader::CACHE_MODE_IGNORE)
    at ./core/io/resource_loader.cpp:526
#18 0x000000000a77067f in ResourceLoader::load (p_path=..., p_type_hint=..., p_cache_mode=ResourceFormatLoader::CACHE_MODE_IGNORE, r_error=0x0) at ./core/io/resource_loader.cpp:444
#19 0x000000000796cad2 in EditorNode::set_addon_plugin_enabled (this=0xe886af0, p_addon=..., p_enabled=true, p_config_changed=false) at ./editor/editor_node.cpp:3662
--Type <RET> for more, q to quit, c to continue without paging--c
#20 0x0000000007956f04 in EditorNode::init_plugins (this=0xe886af0) at ./editor/editor_node.cpp:852
#21 0x000000000776a3db in EditorFileSystem::_first_scan_filesystem (this=0xe1a5320) at ./editor/editor_file_system.cpp:249
#22 0x000000000776e438 in EditorFileSystem::scan (this=0xe1a5320) at ./editor/editor_file_system.cpp:827
#23 0x00000000079558c0 in EditorNode::_notification (this=0xe886af0, p_what=17) at ./editor/editor_node.cpp:639
#24 0x0000000007a47244 in EditorNode::_notificationv (this=0xe886af0, p_notification=17, p_reversed=false) at ./editor/editor_node.h:126
#25 0x000000000abf03dc in Object::notification (this=0xe886af0, p_notification=17, p_reversed=false) at ./core/object/object.cpp:870
#26 0x00000000086ff244 in SceneTree::_process_group (this=0xe0565f0, p_group=0xe056848, p_physics=false) at ./scene/main/scene_tree.cpp:962
#27 0x00000000086ff7bd in SceneTree::_process (this=0xe0565f0, p_physics=false) at ./scene/main/scene_tree.cpp:1039
#28 0x00000000086fd7df in SceneTree::process (this=0xe0565f0, p_time=0.14999999999999947) at ./scene/main/scene_tree.cpp:526
#29 0x0000000005c02d17 in Main::iteration () at main/main.cpp:4103
#30 0x0000000005b4888e in OS_LinuxBSD::run (this=0x7fffffffd090) at platform/linuxbsd/os_linuxbsd.cpp:962
#31 0x0000000005b410b1 in main (argc=2, argv=0x7fffffffd6f8) at platform/linuxbsd/godot_linuxbsd.cpp:85
(gdb) frame 9
#9  0x00000000066de825 in GDScriptCache::get_full_script (p_path=..., r_error=@0x7fffffffaf9c: OK, p_owner=..., p_update_from_disk=false) at ./modules/gdscript/gdscript_cache.cpp:359
359             r_error = script->reload(true);
(gdb) print p_path
$1 = (const String &) @0x28375dd8: {_cowdata = {static MAX_INT = <optimized out>, static REF_COUNT_OFFSET = <optimized out>, static SIZE_OFFSET = <optimized out>, static DATA_OFFSET = <optimized out>, 
    _ptr = 0x274d60b0 U"res://addons/zylann.hterrain/tools/texture_editor/set_editor/texture_set_import_editor.gd"}, static _null = 0 U'\000', static _replacement_char = 65533 U'�'}

[akien-mga]

MRP:

func _ready():
	var _slots_data := []

	var slot_index = 0
	while slot_index < 2:
		var slot = Node.new()
		_slots_data.append(slot)
		slot_index += 1

	var slot : Node = _slots_data[slot_index]

The problem seems to come from the local slot in the while loop which somehow conflicts with the slot local in the parent scope.

If I rename either of them, the bug is resolved.

Edit: Even more minimal. The while seems to be needed too, but the condition doesn't have to make sense.

func _ready():
	var _slots_data := []

	while false:
		var slot = 42
		_slots_data.append(slot)

	var slot : int = _slots_data[0]