illegal declarations should give error at declaration time, not later at instantiation time

[arnetheduck]

In the following snippet, context on line 3 has a bad type, but instead the compiler complains that line 9 is wrong: test.nim(9, 18) Error: invalid type: 'object' in this context: 'proc (): Value' - this is obviously very confusing! if Value is not used in the function declaration, no error at all is given!

type
  Type = ref object 
    context: ref object

type
  Value = ref object
    typ: Type

proc x(): Value =
  nil

[Araq]

Yeah we know, duplicate of some other bug.

[Araq]

BigBoneDaddy: Nope.

[rayman22201]

Bug #3011 maybe? I tried to fix #3011 but it's nasty... It's not clear what is allowed and what not until it's used as a parameter/variable/etc.

@Araq, @timotheecour,

As Araq points out, it seems the way the compiler is designed makes this difficult to catch at declaration time.

As a compromise, maybe it's ok to have it detected at instantiation time, but create a better error message with more context information / better line numbers?
Similar to what I did in the PR: #10354

This is not perfect, because a bad type declaration that is never used will never be caught, but that seems much less harmful than a bad type declaration that is used but the programmer is unable to debug.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. If you think it is still a valid issue, write a comment below; otherwise it will be closed. Thank you for your contributions.

[ringabout]

Now it is even worse. It compiles since Nim v1.0

[bung87]

it compiles and the proc x return type is void.
Nim Compiler Version 1.7.1

[bung87]

!nim c

type
  Type = ref object 
    context: ref object

type
  Value = ref object
    typ: Type

proc x(): Value =
  nil

[github-actions]

@bung87 (collaborator)

devel 👍 $\color{green}\textbf{\large OK}$

Output

Stats

• Started 2023-08-28T05:41:43
• Finished 2023-08-28T05:41:44
• Duration

stable 👍 $\color{green}\textbf{\large OK}$

Output

Stats

• Started 2023-08-28T05:41:44
• Finished 2023-08-28T05:41:45
• Duration

2.0.0 👍 $\color{green}\textbf{\large OK}$

Output

Stats

• Started 2023-08-28T05:41:45
• Finished 2023-08-28T05:41:46
• Duration

1.6.0 👍 $\color{green}\textbf{\large OK}$

Output

Stats

• Started 2023-08-28T05:41:48
• Finished 2023-08-28T05:41:48
• Duration

1.4.0 👍 $\color{green}\textbf{\large OK}$

Output

Stats

• Started 2023-08-28T05:41:51
• Finished 2023-08-28T05:41:51
• Duration

1.2.0 👍 $\color{green}\textbf{\large OK}$

Output

Stats

• Started 2023-08-28T05:42:05
• Finished 2023-08-28T05:42:06
• Duration

1.0.0 👍 $\color{green}\textbf{\large OK}$

Output

Stats

• Started 2023-08-28T05:42:19
• Finished 2023-08-28T05:42:19
• Duration

0.20.2 👎 FAIL

Output

Error: Command failed: nim c --run  -d:nimDebugDlOpen -d:ssl -d:nimDisableCertificateValidation --forceBuild:on --colors:off --verbosity:0 --hints:off --warnings:off --lineTrace:off --nimcache:/home/runner/work/Nim/Nim --out:/home/runner/work/Nim/Nim/temp /home/runner/work/Nim/Nim/temp.nim
/home/runner/work/Nim/Nim/temp.nim(7, 7) Error: invalid type: 'object' in this context: 'proc (): Value' for proc

Stats

• Started 2023-08-28T05:42:28
• Finished 2023-08-28T05:42:28
• Duration

IR

Compiled filesize 81.94 Kb (83,904 bytes)

#define NIM_INTBITS 64
#include "nimbase.h"
#undef LANGUAGE_C
#undef MIPSEB
#undef MIPSEL
#undef PPC
#undef R3000
#undef R4000
#undef i386
#undef linux
#undef mips
#undef near
#undef far
#undef powerpc
#undef unix
#define nimfr_(x, y)
#define nimln_(x, y)
static N_INLINE(void, initStackBottomWith)(void* locals);
N_NOINLINE(void, nimGC_setStackBottom)(void* theStackBottom);
N_LIB_PRIVATE N_NIMCALL(void, systemDatInit000)(void);
N_LIB_PRIVATE N_NIMCALL(void, systemInit000)(void);
N_LIB_PRIVATE N_NIMCALL(void, NimMainModule)(void);
static N_INLINE(void, initStackBottomWith)(void* locals) {
	nimGC_setStackBottom(locals);
}
void PreMainInner(void) {
}
int cmdCount;
char** cmdLine;
char** gEnv;
void PreMain(void) {
	void (*volatile inner)(void);
	inner = PreMainInner;
	systemDatInit000();
	initStackBottomWith((void *)&inner);
	systemInit000();
	(*inner)();
}
N_CDECL(void, NimMainInner)(void) {
	NimMainModule();
}
N_CDECL(void, NimMain)(void) {
	void (*volatile inner)(void);
	PreMain();
	inner = NimMainInner;
	initStackBottomWith((void *)&inner);
	(*inner)();
}
int main(int argc, char** args, char** env) {
	cmdLine = args;
	cmdCount = argc;
	gEnv = env;
	NimMain();
	return nim_program_result;
}
N_LIB_PRIVATE N_NIMCALL(void, NimMainModule)(void) {
{
}
}

AST

nnkStmtList.newTree(
  nnkTypeSection.newTree(
    nnkTypeDef.newTree(
      newIdentNode("Type"),
      newEmptyNode(),
      nnkRefTy.newTree(
        nnkObjectTy.newTree(
          newEmptyNode(),
          newEmptyNode(),
          nnkRecList.newTree(
            nnkIdentDefs.newTree(
              newIdentNode("context"),
              nnkRefTy.newTree(
                nnkObjectTy.newTree(
                )
              ),
              newEmptyNode()
            )
          )
        )
      )
    )
  ),
  nnkTypeSection.newTree(
    nnkTypeDef.newTree(
      newIdentNode("Value"),
      newEmptyNode(),
      nnkRefTy.newTree(
        nnkObjectTy.newTree(
          newEmptyNode(),
          newEmptyNode(),
          nnkRecList.newTree(
            nnkIdentDefs.newTree(
              newIdentNode("typ"),
              newIdentNode("Type"),
              newEmptyNode()
            )
          )
        )
      )
    )
  ),
  nnkProcDef.newTree(
    newIdentNode("x"),
    newEmptyNode(),
    newEmptyNode(),
    nnkFormalParams.newTree(
      newIdentNode("Value")
    ),
    newEmptyNode(),
    newEmptyNode(),
    nnkStmtList.newTree(
      newNilLit()
    )
  )
)

??? ➡️ 🐛

Diagnostics

The commit that introduced the bug can not be found, but the bug is in the commits:

• #05d647398
• #4c8a02165
• #7e6c3f368
• #65a2b3bb6
• #8dfebb328
• #de2c27129
• #022cd2c14

(Can not find the commit because Nim can not be re-built commit-by-commit to bisect).

Stats

• GCC 11.4.0
• LibC 2.35
• Valgrind 3.18.1
• NodeJS 17.1
• Linux 5.15.0
• Created 2023-08-28T05:41:12Z
• Comments 7
• Commands nim c --run -d:nimDebugDlOpen -d:ssl -d:nimDisableCertificateValidation --forceBuild:on --colors:off --verbosity:0 --hints:off --warnings:off --lineTrace:off --nimcache:/home/runner/work/Nim/Nim --out:/home/runner/work/Nim/Nim/temp /home/runner/work/Nim/Nim/temp.nim

🤖 Bug found in 44 minutes bisecting 232 commits at 5 commits per second.