[PATCH] support: Increase usability of TEST_COMPARE

[fweimer at redhat dot com (Florian Weimer)]

The previous implementation of the TEST_COMPARE macro would fail
to compile code like this:

  int ret = res_send (query, sizeof (query), buf, sizeof (buf));
  TEST_COMPARE (ret,
                sizeof (query)
                + 2             /* Compression reference.  */
                + 2 + 2 + 4 + 2 /* Type, class, TTL, RDATA length.  */
                + 1             /* Pascal-style string length.  */
                + strlen (expected_name));

This resulted in a failed static assertion, "integer conversions
may alter sign of operands".  A user of the TEST_COMPARE would have
to add a cast to fix this.

This patch reverts to the original proposed solution of a run-time
check, making TEST_COMPARE usable for comparisons of numbers with
types with different signedness in more contexts.

2018-01-08  Florian Weimer  <fweimer@redhat.com>

	* support/check.h (TEST_COMPARE): Allow sign mismatch at compile
	time.  Pass positive flag instead of negative flag to
	support_test_compare_failure.
	(support_test_compare_failure): Change negative parameter to
	positive.
	* support/support_test_compare_failure.c (report)
	(support_test_compare_failure): Likewise.
	* support/tst-test_compare.c (return_ssize_t, return_int): New.
	(do_test): Check int/size_t, ssize_t/size_t comparisons.

diff --git a/support/check.h b/support/check.h
index de8fce0dc1..2ac25a187c 100644
--- a/support/check.h
+++ b/support/check.h
@@ -95,7 +95,9 @@ void support_record_failure (void);
     typedef __typeof__ (+ (right)) __right_type;                        \
     __left_type __left_value = (left);                                  \
     __right_type __right_value = (right);                               \
-    /* Prevent use with floating-point and boolean types.  */           \
+    int __left_is_positive = __left_value > 0;                          \
+    int __right_is_positive = __right_value > 0;                        \
+    /* Prevent use with floating-point types.  */                       \
     _Static_assert ((__left_type) 1.0 == (__left_type) 1.5,             \
                     "left value has floating-point type");              \
     _Static_assert ((__right_type) 1.0 == (__right_type) 1.5,           \
@@ -105,33 +107,18 @@ void support_record_failure (void);
                     "left value fits into long long");                  \
     _Static_assert (sizeof (__right_value) <= sizeof (long long),       \
                     "right value fits into long long");                 \
-    /* Make sure that integer conversions does not alter the sign.   */ \
-    enum                                                                \
-    {                                                                   \
-      __left_is_unsigned = (__left_type) -1 > 0,                        \
-      __right_is_unsigned = (__right_type) -1 > 0,                      \
-      __unsigned_left_converts_to_wider = (__left_is_unsigned           \
-                                           && (sizeof (__left_value)    \
-                                               < sizeof (__right_value))), \
-      __unsigned_right_converts_to_wider = (__right_is_unsigned         \
-                                            && (sizeof (__right_value)  \
-                                                < sizeof (__left_value))) \
-    };                                                                  \
-    _Static_assert (__left_is_unsigned == __right_is_unsigned           \
-                    || __unsigned_left_converts_to_wider                \
-                    || __unsigned_right_converts_to_wider,              \
-                    "integer conversions may alter sign of operands");  \
     /* Compare the value.  */                                           \
-    if (__left_value != __right_value)                                  \
+    if (__left_value != __right_value                                   \
+        || __left_is_positive != __right_is_positive)                   \
       /* Pass the sign for printing the correct value.  */              \
       support_test_compare_failure                                      \
         (__FILE__, __LINE__,                                            \
-         #left, __left_value, __left_value < 0, sizeof (__left_type),   \
-         #right, __right_value, __right_value < 0, sizeof (__right_type)); \
+         #left, __left_value, __left_is_positive, sizeof (__left_type), \
+         #right, __right_value, __right_is_positive, sizeof (__right_type)); \
   })
 
-/* Internal implementation of TEST_COMPARE.  LEFT_NEGATIVE and
-   RIGHT_NEGATIVE are used to store the sign separately, so that both
+/* Internal implementation of TEST_COMPARE.  LEFT_POSITIVE and
+   RIGHT_POSITIVE are used to store the sign separately, so that both
    unsigned long long and long long arguments fit into LEFT_VALUE and
    RIGHT_VALUE, and the function can still print the original value.
    LEFT_SIZE and RIGHT_SIZE specify the size of the argument in bytes,
@@ -139,11 +126,11 @@ void support_record_failure (void);
 void support_test_compare_failure (const char *file, int line,
                                    const char *left_expr,
                                    long long left_value,
-                                   int left_negative,
+                                   int left_positive,
                                    int left_size,
                                    const char *right_expr,
                                    long long right_value,
-                                   int right_negative,
+                                   int right_positive,
                                    int right_size);
 
 
diff --git a/support/support_test_compare_failure.c b/support/support_test_compare_failure.c
index a789283f86..e5596fd121 100644
--- a/support/support_test_compare_failure.c
+++ b/support/support_test_compare_failure.c
@@ -20,14 +20,14 @@
 #include <support/check.h>
 
 static void
-report (const char *which, const char *expr, long long value, int negative,
+report (const char *which, const char *expr, long long value, int positive,
         int size)
 {
   printf ("  %s: ", which);
-  if (negative)
-    printf ("%lld", value);
-  else
+  if (positive)
     printf ("%llu", (unsigned long long) value);
+  else
+    printf ("%lld", value);
   unsigned long long mask
     = (~0ULL) >> (8 * (sizeof (unsigned long long) - size));
   printf (" (0x%llx); from: %s\n", (unsigned long long) value & mask, expr);
@@ -37,11 +37,11 @@ void
 support_test_compare_failure (const char *file, int line,
                               const char *left_expr,
                               long long left_value,
-                              int left_negative,
+                              int left_positive,
                               int left_size,
                               const char *right_expr,
                               long long right_value,
-                              int right_negative,
+                              int right_positive,
                               int right_size)
 {
   support_record_failure ();
@@ -50,6 +50,6 @@ support_test_compare_failure (const char *file, int line,
             file, line, left_size * 8, right_size * 8);
   else
     printf ("%s:%d: numeric comparison failure\n", file, line);
-  report (" left", left_expr, left_value, left_negative, left_size);
-  report ("right", right_expr, right_value, right_negative, right_size);
+  report (" left", left_expr, left_value, left_positive, left_size);
+  report ("right", right_expr, right_value, right_positive, right_size);
 }
diff --git a/support/tst-test_compare.c b/support/tst-test_compare.c
index 340268fadf..123ba1bc3c 100644
--- a/support/tst-test_compare.c
+++ b/support/tst-test_compare.c
@@ -42,6 +42,22 @@ struct bitfield
   unsigned long long int u63 : 63;
 };
 
+/* Functions which return signed sizes are common, so test that these
+   results can readily checked using TEST_COMPARE.  */
+
+static int
+return_ssize_t (void)
+{
+  return 4;
+}
+
+static int
+return_int (void)
+{
+  return 4;
+}
+
+
 static int
 do_test (void)
 {
@@ -53,6 +69,8 @@ do_test (void)
     unsigned short u16 = 3;
     TEST_COMPARE (i8, u16);
   }
+  TEST_COMPARE (return_ssize_t (), sizeof (char[4]));
+  TEST_COMPARE (return_int (), sizeof (char[4]));
 
   struct bitfield bitfield = { 0 };
   TEST_COMPARE (bitfield.i2, bitfield.i3);