Enhance function parsing

[DrXiao]

Since the previous parser incorrectly handles a function with a forward declaration before implementation, the code generator may produce wrong instructions due to the incorrect information provided by the frontend.

For example, consider the following example:

int func(char *a);

int func(char *a)
{
    return *a;
}

int main(void)
{
    char a = 10;
    return func(&a);
}

After parsing the forward declaration of func, it is added to the function list, and its parameter a is recorded with the type char *. When the function implementation is later parsed, the parser processes the declaration again, but the pointer level of a is accumulated, causing the type of a to become char **.

This can be observed when using shecc to compile and output the IRs:

==<START OF INSN DUMP>==
def int @func(char** %a) {
	%.t0 = (%a), 4
	ret %.t0
}
...

---

Additionally, if a function with a forward declaration differs from the later declaration, shecc still continues to parse the source instead of reporting an error:

void func(void);

int **func(void)
{
    return 3;
}

int main()
{
    func();
    return 0;
}

In the above case, shecc considers func to be a function of type int **(void).

---

Therefore, the proposed changes enhance the implementation of the parser to resolve the above issues.

• Reset the pointer level of a parsed variable if it is a function parameter.
• When parsing the function that already exists in the function list, validate that its return type and the data types of all parameters match the previous declaration.

---

Summary by cubic

Fix function parsing for forward-declared functions to keep parameter types correct and to error on conflicting declarations, preventing incorrect IR generation.

• Bug Fixes
  • Reset parameter pointer level during parsing to stop pointer accumulation (e.g., char* incorrectly becoming char**).
  • Validate redeclarations against the first declaration: return type and pointer level, parameter count and types, and variadic flag. Abort with clear “before/after” signatures on mismatch.
  • Added tests covering the normal case and conflicts (return type, parameter count/type, variadic).

[DrXiao]

For the second example, the improved shecc will report an error message as follows due to conflicting types for func:

$ qemu-arm out/shecc-stage2.elf --no-libc -o example2 example2.c
Error: conflicting types for the function func.
before: void func()
after: int **func()

Other examples:

Error: confilcting number of arguments for the function func.
before: void func(void *a)
after: void func(void *a, int x)

Error: confilcting types for the function func.
before: void func(void *a, char x)
after: void func(void *a, int x)

Error: conflicting types for the function func.
before: void func(void *a)
after: void func(void *a, ...)

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (all 1 issues)

Understand the root cause of the following 1 issues and fix them.


<file name="tests/driver.sh">

<violation number="1" location="tests/driver.sh:5590">
The new compile-error tests return values from `void`/pointer functions (e.g., `return 3;`), so they will always trigger diagnostics unrelated to the prototype mismatch, meaning the tests won’t catch the regression they target.</violation>
</file>

_{React with 👍 or 👎 to teach cubic. Mention @cubic-dev-ai to give feedback, ask questions, or re-run the review.}

[DrXiao]

Add handling for const keyword:

Error: confilcting types for the function func.
before: void func(int *a, char x)
after: void func(const int *a, char x)

Error: conflicting types for the function func.
before: void *func(int *a, char x)
after: const void *func(int *a, char x)

[jserv]

Thank @DrXiao for contributing!