[clang][BoundsSafety] Extend `-Wvla-potential-size-confusion` for struct fields and bounds annotations

[rapidsna]

#129772

-Wvla-potential-size-confusion diagnoses when n references the file scope variable and not the parameter.

int n;
void func(int array[n], int n);

We may want to extend it to diagnose on situations mentioned in the PR:

• Diagnosing a similar situation in structures. e.g.,

int n;
struct S {
  int n;
  int array[sizeof(n)]; // Refers to outer n, not member n
};

• Diagnosing with constant-size arrays (requires tracking the expression for the constant-size array in the QualType) e.g.,

constexpr int n = 12;
void func(int array[n], int n);

• Potentially, also diagnosing with any ambiguous situations with bounds annotations like below (with or without the -fexperimental-late-parse-attributes flag:

constexpr int n;
struct foo {
  int * ptr __counted_by(n);
  int n;
};

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Yeoul Na (rapidsna)

https://github.com//pull/129772

-Wvla-potential-size-confusion diagnoses when n references the file scope variable and not the parameter.

int n;
void func(int array[n], int n);

We may want to extend it to diagnose on situations mentioned in the PR:

• Diagnosing a similar situation in structures. e.g.,

int n;
struct S {
  int n;
  int array[sizeof(n)]; // Refers to outer n, not member n
};

• Diagnosing with constant-size arrays (requires tracking the expression for the constant-size array in the QualType) e.g.,

constexpr int n = 12;
void func(int array[n], int n);

• Potentially, also diagnosing with any ambiguous situations with bounds annotations like below (with or without the -fexperimental-late-parse-attributes flag:

constexpr int n;
struct foo {
  int * ptr __counted_by(n);
  int n;
};

[cor3ntin]

@AaronBallman