Re: guc: make dereference style consistent in check_backtrace_functions

> On Feb 26, 2026, at 20:37, Álvaro Herrera <alvherre@kurilemu.de> wrote:
> 
> There is at least one more place in the code where this is done.
> 

I did a search with the command: grep -RInE '\*[[:space:]]*[A-Za-z_][A-Za-z0-9_]*\[0\]' src contrib --include='*.c'

Excluding irrelevant results, there are 3 more occurrences:

1 - contrib/basic_archive/basic_archive.c line 105
```
	if (*newval == NULL || *newval[0] == '\0')
		return true;
```

Here, the code checks *newval first, which implies that the subsequent *newval[0] is unintentional syntax.

2 - src/interfaces/ecpg/pgtypeslib/interval.c line 62
```
int
DecodeInterval(char **field, int *ftype, int nf,	/* int range, */
			   int *dtype, struct /* pg_ */ tm *tm, fsec_t *fsec)
{
  ...
	if (IntervalStyle == INTSTYLE_SQL_STANDARD && *field[0] == '-')
	{
		/* Check for additional explicit signs */
		bool		more_signs = false;

		for (i = 1; i < nf; i++)
		{
			if (*field[i] == '-' || *field[i] == '+')
			{
				more_signs = true;
				break;
			}
		}
```

3 - src/backend/utils/adt/datatime.c line 3522
```
int
DecodeInterval(char **field, int *ftype, int nf, int range,
			   int *dtype, struct pg_itm_in *itm_in)
{
 ...
	if (IntervalStyle == INTSTYLE_SQL_STANDARD && nf > 0 && *field[0] == '-')
	{
		force_negative = true;
		/* Check for additional explicit signs */
		for (i = 1; i < nf; i++)
		{
			if (*field[i] == '-' || *field[i] == '+')
			{
				force_negative = false;
				break;
			}
		}
	}
```

Where 2&3 makes this patch more interesting.

Both occurrences are inside functions named DecodeInterval. For non-zero i, the code also performs *field[i]:

Given this code has been there for years, I don’t believe it is a bug. I checked the callers of DecodeInterval in both files and found that field is defined as:
```
    char *field[MAXDATEFIELDS];
```

This explains why *field[i] works; it is doing the intended thing by getting the first character of the string at array position i.

However, since the precedence between the [] and * operators frequently confuses people, I suggest adding parentheses to make the intention explicit as *(field[i]). Furthermore, I think we should change the function signatures to use the type char *field[] to reflect the actual type the functions expect. If a caller were to pass a true char ** typed field to DecodeInterval, the current logic would result in a bug.

See the attached diff for my suggested changes.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/