Compiler error when trying to infer generics with a nested map

[hungrybluedev]

V doctor:

V full version: V 0.4.9 7b9b3dd
OS: macos, macOS, 15.1.1, 24B91
Processor: 10 cpus, 64bit, little endian, Apple M1 Pro

getwd: /Users/subhomoyhaldar/Documents/GitHub/VProjects/Consultation/vhammll
vexe: /Users/subhomoyhaldar/Documents/GitHub/v-main/v
vexe mtime: 2025-01-01 10:54:25

vroot: OK, value: /Users/subhomoyhaldar/Documents/GitHub/v-main
VMODULES: OK, value: /Users/subhomoyhaldar/.vmodules
VTMP: OK, value: /tmp/v_501

Git version: git version 2.39.5 (Apple Git-154)
Git vroot status: weekly.2024.53
.git/config present: true

CC version: Apple clang version 16.0.0 (clang-1600.0.26.6)
emcc version: N/A
thirdparty/tcc status: thirdparty-macos-arm64 713692d4

What did you do?
./v -g -o vdbg cmd/v && ./vdbg scratch/error.v

import x.json2

struct CrossVerifyResult {
	confusion_matrix_map map[string]map[string]f64
}

fn main() {
	x := json2.decode[CrossVerifyResult]('')!
	dump(x)
}

What did you expect to see?

I was expecting a compilation error or success.

What did you see instead?

================ V panic ================
   module: v.ast
 function: default_table_panic_handler()
  message: table.sym: invalid type (typ=ast.Type(0x0 = 0) idx=0). Compiler bug. This should never happen. Please report the bug using `v bug file.v`.

     file: /Users/subhomoyhaldar/Documents/GitHub/v-main/vlib/v/ast/table.v:131
   v hash: 7b9b3dd
=========================================
0   vdbg                                0x0000000102bfcdac v__ast__Table_panic + 0
1   vdbg                                0x0000000102bfcdf4 v__ast__Table_panic + 72
2   vdbg                                0x0000000102bf0edc v__ast__Table_sym + 312
3   vdbg                                0x0000000102c67274 v__checker__Checker_infer_fn_generic_types + 4904
4   vdbg                                0x0000000102ceb2b8 v__checker__Checker_fn_call + 42136
5   vdbg                                0x0000000102cacd90 v__checker__Checker_call_expr + 496
6   vdbg                                0x0000000102c51398 v__checker__Checker_expr + 3544
7   vdbg                                0x0000000102c47b9c v__checker__Checker_assign_stmt + 1052
8   vdbg                                0x0000000102c6af6c v__checker__Checker_stmt + 396
9   vdbg                                0x0000000102c7a278 v__checker__Checker_stmts_ending_with_expression + 612
10  vdbg                                0x0000000102c93a00 v__checker__Checker_stmts + 60
11  vdbg                                0x0000000102cb7f00 v__checker__Checker_if_expr + 9920
12  vdbg                                0x0000000102c520e8 v__checker__Checker_expr + 6952
13  vdbg                                0x0000000102c6b520 v__checker__Checker_stmt + 1856
14  vdbg                                0x0000000102c7a278 v__checker__Checker_stmts_ending_with_expression + 612
15  vdbg                                0x0000000102c93a00 v__checker__Checker_stmts + 60
16  vdbg                                0x0000000102c9be90 v__checker__Checker_for_in_stmt + 8876
17  vdbg                                0x0000000102c6b884 v__checker__Checker_stmt + 2724
18  vdbg                                0x0000000102c7a278 v__checker__Checker_stmts_ending_with_expression + 612
19  vdbg                                0x0000000102c93a00 v__checker__Checker_stmts + 60
20  vdbg                                0x0000000102c98b78 v__checker__Checker_fn_decl + 20832
21  vdbg                                0x0000000102c6e0cc v__checker__Checker_post_process_generic_fns + 972
22  vdbg                                0x0000000102c6d03c v__checker__Checker_check_files + 3008
23  vdbg                                0x0000000102e7ddec v__builder__Builder_middle_stages + 208
24  vdbg                                0x0000000102e7faec v__builder__Builder_front_and_middle_stages + 120
25  vdbg                                0x0000000102e93fe4 v__builder__cbuilder__gen_c + 84
26  vdbg                                0x0000000102e93d9c v__builder__cbuilder__build_c + 288
27  vdbg                                0x0000000102e93c24 v__builder__cbuilder__compile_c + 568
28  vdbg                                0x0000000102e8dcf8 v__builder__Builder_rebuild + 108
29  vdbg                                0x0000000102e8d6e4 v__builder__compile + 92
30  vdbg                                0x0000000102e97228 main__rebuild + 164
31  vdbg                                0x0000000102e96e14 main__main + 3780
32  vdbg                                0x0000000102e9aa40 main + 76
33  dyld                                0x00000001941b4274 start + 2840

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_{Huly®: V_0.6-21760}