enum_flags to_string

This commit introduces shared infrastructure that can be used to
implement enum_flags -> to_string functions.  With this, if we want to
support converting a given enum_flags specialization to string, we
just need to implement a function that provides the enumerator->string
mapping, like so:

 enum some_flag
   {
     SOME_FLAG1 = 1 << 0,
     SOME_FLAG2 = 1 << 1,
     SOME_FLAG3 = 1 << 2,
   };

 DEF_ENUM_FLAGS_TYPE (some_flag, some_flags);

 static std::string
 to_string (some_flags flags)
 {
   static constexpr some_flags::string_mapping mapping[] = {
     MAP_ENUM_FLAG (SOME_FLAG1),
     MAP_ENUM_FLAG (SOME_FLAG2),
     MAP_ENUM_FLAG (SOME_FLAG3),
   };
   return flags.to_string (mapping);
 }

.. and then to_string(SOME_FLAG2 | SOME_FLAG3) produces a string like
"0x6 [SOME_FLAG2 SOME_FLAG3]".

If we happen to forget to update the mapping array when we introduce a
new enumerator, then the string representation will pretty-print the
flags it knows about, and then the leftover flags in hex (one single
number).  For example, if we had missed mapping SOME_FLAG2 above, we'd
end up with:

  to_string(SOME_FLAG2 | SOME_FLAG3)  => "0x6 [SOME_FLAG2 0x4]");

Other than in the unit tests included, no actual usage of the
functionality is added in this commit.

Approved-By: Simon Marchi <simon.marchi@efficios.com>
Change-Id: I835de43c33d13bc0c95132f42c3f97318b875779

1 files changed, 63 insertions, 6 deletions

diff --git a/gdb/unittests/enum-flags-selftests.c b/gdb/unittests/enum-flags-selftests.c
index 0780fb8..2d3c555 100644
--- a/gdb/unittests/enum-flags-selftests.c
+++ b/gdb/unittests/enum-flags-selftests.c
@@ -359,21 +359,47 @@ CHECK_VALID (true,  bool, NF (1) == char (1))
 
 enum test_flag
   {
-    FLAG1 = 1 << 1,
-    FLAG2 = 1 << 2,
-    FLAG3 = 1 << 3,
+    FLAG1 = 1 << 0,
+    FLAG2 = 1 << 1,
+    FLAG3 = 1 << 2,
+    FLAG4 = 1 << 3,
   };
 
 enum test_uflag : unsigned
   {
-    UFLAG1 = 1 << 1,
-    UFLAG2 = 1 << 2,
-    UFLAG3 = 1 << 3,
+    UFLAG1 = 1 << 0,
+    UFLAG2 = 1 << 1,
+    UFLAG3 = 1 << 2,
+    UFLAG4 = 1 << 3,
   };
 
 DEF_ENUM_FLAGS_TYPE (test_flag, test_flags);
 DEF_ENUM_FLAGS_TYPE (test_uflag, test_uflags);
 
+/* to_string enumerator->string mapping functions used to test
+   enum_flags::to_string.  These intentionally miss mapping a couple
+   enumerators each (xFLAG2, xFLAG4).  */
+
+static std::string
+to_string_flags (test_flags flags)
+{
+  static constexpr test_flags::string_mapping mapping[] = {
+    MAP_ENUM_FLAG (FLAG1),
+    MAP_ENUM_FLAG (FLAG3),
+  };
+  return flags.to_string (mapping);
+}
+
+static std::string
+to_string_uflags (test_uflags flags)
+{
+  static constexpr test_uflags::string_mapping mapping[] = {
+    MAP_ENUM_FLAG (UFLAG1),
+    MAP_ENUM_FLAG (UFLAG3),
+  };
+  return flags.to_string (mapping);
+}
+
 static void
 self_test ()
 {
@@ -581,6 +607,37 @@ self_test ()
 
     SELF_CHECK (ok);
   }
+
+  /* Check string conversion.  */
+  {
+    SELF_CHECK (to_string_uflags (0)
+		== "0x0 []");
+    SELF_CHECK (to_string_uflags (UFLAG1)
+		== "0x1 [UFLAG1]");
+    SELF_CHECK (to_string_uflags (UFLAG1 | UFLAG3)
+		== "0x5 [UFLAG1 UFLAG3]");
+    SELF_CHECK (to_string_uflags (UFLAG1 | UFLAG2 | UFLAG3)
+		== "0x7 [UFLAG1 UFLAG3 0x2]");
+    SELF_CHECK (to_string_uflags (UFLAG2)
+		== "0x2 [0x2]");
+    /* Check that even with multiple unmapped flags, we only print one
+       unmapped hex number (0xa, in this case).  */
+    SELF_CHECK (to_string_uflags (UFLAG1 | UFLAG2 | UFLAG3 | UFLAG4)
+		== "0xf [UFLAG1 UFLAG3 0xa]");
+
+    SELF_CHECK (to_string_flags (0)
+		== "0x0 []");
+    SELF_CHECK (to_string_flags (FLAG1)
+		== "0x1 [FLAG1]");
+    SELF_CHECK (to_string_flags (FLAG1 | FLAG3)
+		== "0x5 [FLAG1 FLAG3]");
+    SELF_CHECK (to_string_flags (FLAG1 | FLAG2 | FLAG3)
+		== "0x7 [FLAG1 FLAG3 0x2]");
+    SELF_CHECK (to_string_flags (FLAG2)
+		== "0x2 [0x2]");
+    SELF_CHECK (to_string_flags (FLAG1 | FLAG2 | FLAG3 | FLAG4)
+		== "0xf [FLAG1 FLAG3 0xa]");
+  }
 }
 
 } /* namespace enum_flags_tests */