Simplify jsonfuncs.c code by using strtoint() not strtol().

Explicitly testing for INT_MIN and INT_MAX isn't particularly good
style; it's tedious and may draw useless compiler warnings on
machines where int and long are the same width.  We invented
strtoint() precisely for this usage, so use that instead.

While here, remove gratuitous variations in the way the tests for
did-strtoint-succeed were spelled.  Also, avoid attempting to
negate INT_MIN; that would probably work given that the result
is implicitly cast to uint32, but I think it's nominally undefined
behavior.

Per gripe from Ranier Vilela, though this isn't his proposed patch.

Discussion: https://postgr.es/m/CAEudQAqge3QfzoBRhe59QrB_5g+NmQUj2QpzqZ9Nc7QepXGAEw@mail.gmail.com

src/backend/utils/adt/jsonfuncs.c

@@ -19,6 +19,7 @@
 #include "access/htup_details.h"
 #include "catalog/pg_type.h"
 #include "common/jsonapi.h"
+#include "common/string.h"
 #include "fmgr.h"
 #include "funcapi.h"
 #include "lib/stringinfo.h"
@@ -1026,15 +1027,15 @@ get_path_all(FunctionCallInfo fcinfo, bool as_text)
 		 */
 		if (*tpath[i] != '\0')
 		{
-			long		ind;
+			int			ind;
 			char	   *endptr;
 
 			errno = 0;
-			ind = strtol(tpath[i], &endptr, 10);
+			ind = strtoint(tpath[i], &endptr, 10);
-			if (*endptr == '\0' && errno == 0 && ind <= INT_MAX && ind >= INT_MIN)
+			if (endptr == tpath[i] || *endptr != '\0' || errno != 0)
-				ipath[i] = (int) ind;
-			else
 				ipath[i] = INT_MIN;
+			else
+				ipath[i] = ind;
 		}
 		else
 			ipath[i] = INT_MIN;
@@ -1533,15 +1534,14 @@ jsonb_get_element(Jsonb *jb, Datum *path, int npath, bool *isnull, bool as_text)
 		}
 		else if (have_array)
 		{
-			long		lindex;
+			int			lindex;
 			uint32		index;
 			char	   *indextext = TextDatumGetCString(path[i]);
 			char	   *endptr;
 
 			errno = 0;
-			lindex = strtol(indextext, &endptr, 10);
+			lindex = strtoint(indextext, &endptr, 10);
-			if (endptr == indextext || *endptr != '\0' || errno != 0 ||
+			if (endptr == indextext || *endptr != '\0' || errno != 0)
-				lindex > INT_MAX || lindex < INT_MIN)
 			{
 				*isnull = true;
 				return PointerGetDatum(NULL);
@@ -1562,7 +1562,7 @@ jsonb_get_element(Jsonb *jb, Datum *path, int npath, bool *isnull, bool as_text)
 
 				nelements = JsonContainerSize(container);
 
-				if (-lindex > nelements)
+				if (lindex == INT_MIN || -lindex > nelements)
 				{
 					*isnull = true;
 					return PointerGetDatum(NULL);
@@ -1675,7 +1675,6 @@ push_path(JsonbParseState **st, int level, Datum *path_elems,
 	 * end, the access index must be normalized by level.
 	 */
 	enum jbvType *tpath = palloc0((path_len - level) * sizeof(enum jbvType));
-	long		lindex;
 	JsonbValue	newkey;
 
 	/*
@@ -1687,6 +1686,7 @@ push_path(JsonbParseState **st, int level, Datum *path_elems,
 	{
 		char	   *c,
 				   *badp;
+		int			lindex;
 
 		if (path_nulls[i])
 			break;
@@ -1697,9 +1697,8 @@ push_path(JsonbParseState **st, int level, Datum *path_elems,
 		 */
 		c = TextDatumGetCString(path_elems[i]);
 		errno = 0;
-		lindex = strtol(c, &badp, 10);
+		lindex = strtoint(c, &badp, 10);
-		if (errno != 0 || badp == c || *badp != '\0' || lindex > INT_MAX ||
+		if (badp == c || *badp != '\0' || errno != 0)
-			lindex < INT_MIN)
 		{
 			/* text, an object is expected */
 			newkey.type = jbvString;
@@ -1720,7 +1719,6 @@ push_path(JsonbParseState **st, int level, Datum *path_elems,
 
 			tpath[i - level] = jbvArray;
 		}
-
 	}
 
 	/* Insert an actual value for either an object or array */
@@ -5138,18 +5136,15 @@ setPathArray(JsonbIterator **it, Datum *path_elems, bool *path_nulls,
 	if (level < path_len && !path_nulls[level])
 	{
 		char	   *c = TextDatumGetCString(path_elems[level]);
-		long		lindex;
 		char	   *badp;
 
 		errno = 0;
-		lindex = strtol(c, &badp, 10);
+		idx = strtoint(c, &badp, 10);
-		if (errno != 0 || badp == c || *badp != '\0' || lindex > INT_MAX ||
+		if (badp == c || *badp != '\0' || errno != 0)
-			lindex < INT_MIN)
 			ereport(ERROR,
 					(errcode(ERRCODE_INVALID_TEXT_REPRESENTATION),
 					 errmsg("path element at position %d is not an integer: \"%s\"",
 							level + 1, c)));
-		idx = lindex;
 	}
 	else
 		idx = nelems;