[warnings 3/7] Suppress warnings about conversions between char * and unsigned char *.

[Ben Pfaff]

For some time PSPP has used "unsigned char *" for string data and "Char *"
for most other strings.  Transforming between these properly generally
involves recoding, and there are some places where this is possibly
missing.  The usual way to "fix" these warnings would be to insert casts,
but this would not fix the problem, just suppress the warnings, and it is
difficult to "grep" for casts so they would be hard to find for fixing
later.

This commit doesn't actually fix the problems, but it does suppress the
warnings while making them easy to find later: just grep for CHAR_CAST_BUG.
---
 src/language/expressions/operations.def |    9 ++++++---
 src/language/lexer/value-parser.c       |   27 ++++++++++++++++-----------
 src/language/xforms/compute.c           |   12 +++++++-----
 src/language/xforms/recode.c            |   10 ++++++----
 src/libpspp/cast.h                      |   25 ++++++++++++++++++++++++-
 src/ui/syntax-gen.c                     |   22 +++++++++++++---------
 6 files changed, 72 insertions(+), 33 deletions(-)

diff --git a/src/language/expressions/operations.def 
b/src/language/expressions/operations.def
index 844cab7..c25f113 100644
--- a/src/language/expressions/operations.def
+++ b/src/language/expressions/operations.def
@@ -961,7 +961,8 @@ absorb_miss no_opt string operator VEC_ELEM_STR (idx)
   if (idx >= 1 && idx <= vector_get_var_cnt (v))
     {
       struct variable *var = vector_get_var (v, (size_t) idx - 1);
-      return copy_string (e, case_str (c, var), var_get_width (var));
+      return copy_string (e, CHAR_CAST_BUG (char *, case_str (c, var)),
+                          var_get_width (var));
     }
   else
     {
@@ -1029,7 +1030,8 @@ no_opt perm_only string function LAG (str_var v, pos_int 
n_before)
 {
   const struct ccase *c = lagged_case (ds, n_before);
   if (c != NULL)
-    return copy_string (e, case_str (c, v), var_get_width (v));
+    return copy_string (e, CHAR_CAST_BUG (char *, case_str (c, v)),
+                        var_get_width (v));
   else
     return empty_string;
 }
@@ -1040,7 +1042,8 @@ no_opt perm_only string function LAG (str_var v)
 {
   const struct ccase *c = lagged_case (ds, 1);
   if (c != NULL)
-    return copy_string (e, case_str (c, v), var_get_width (v));
+    return copy_string (e, CHAR_CAST_BUG (char *, case_str (c, v)),
+                        var_get_width (v));
   else
     return empty_string;
 }
diff --git a/src/language/lexer/value-parser.c 
b/src/language/lexer/value-parser.c
index c780d86..c492658 100644
--- a/src/language/lexer/value-parser.c
+++ b/src/language/lexer/value-parser.c
@@ -1,5 +1,5 @@
 /* PSPP - a program for statistical analysis.
-   Copyright (C) 2005, 2006, 2009 Free Software Foundation, Inc.
+   Copyright (C) 2005, 2006, 2009, 2010 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -15,14 +15,18 @@
    along with this program.  If not, see <http://www.gnu.org/licenses/>. */
 
 #include <config.h>
+
 #include "value-parser.h"
+
 #include <stdbool.h>
-#include <data/data-in.h>
-#include <libpspp/message.h>
-#include "lexer.h"
-#include <libpspp/str.h>
-#include <data/value.h>
-#include <data/format.h>
+
+#include "data/data-in.h"
+#include "data/format.h"
+#include "data/value.h"
+#include "language/lexer/lexer.h"
+#include "libpspp/cast.h"
+#include "libpspp/message.h"
+#include "libpspp/str.h"
 
 #include "gettext.h"
 #define _(msgid) gettext (msgid)
@@ -133,12 +137,13 @@ parse_value (struct lexer *lexer, union value *v, int 
width)
        return false;
       v->f = lex_tokval (lexer);
     }
-  else
+  else if (lex_force_string (lexer))
     {
-      if (!lex_force_string (lexer))
-       return false;
-      value_copy_str_rpad (v, width, ds_cstr (lex_tokstr (lexer)), ' ');
+      const char *s = ds_cstr (lex_tokstr (lexer));
+      value_copy_str_rpad (v, width, CHAR_CAST_BUG (const uint8_t *, s), ' ');
     }
+  else
+    return false;
 
   lex_get (lexer);
 
diff --git a/src/language/xforms/compute.c b/src/language/xforms/compute.c
index 09fc215..a508933 100644
--- a/src/language/xforms/compute.c
+++ b/src/language/xforms/compute.c
@@ -1,5 +1,5 @@
 /* PSPP - a program for statistical analysis.
-   Copyright (C) 1997-9, 2000, 2009 Free Software Foundation, Inc.
+   Copyright (C) 1997-9, 2000, 2009, 2010 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -173,10 +173,11 @@ compute_str (void *compute_, struct ccase **c, casenumber 
case_num)
   if (compute->test == NULL
       || expr_evaluate_num (compute->test, *c, case_num) == 1.0)
     {
+      char *s;
+
       *c = case_unshare (*c);
-      expr_evaluate_str (compute->rvalue, *c, case_num,
-                         case_str_rw (*c, compute->variable),
-                         compute->width);
+      s = CHAR_CAST_BUG (char *, case_str_rw (*c, compute->variable));
+      expr_evaluate_str (compute->rvalue, *c, case_num, s, compute->width);
     }
 
   return TRNS_CONTINUE;
@@ -216,7 +217,8 @@ compute_str_vec (void *compute_, struct ccase **c, 
casenumber case_num)
       vr = vector_get_var (compute->vector, rindx - 1);
       *c = case_unshare (*c);
       expr_evaluate_str (compute->rvalue, *c, case_num,
-                         case_str_rw (*c, vr), var_get_width (vr));
+                         CHAR_CAST_BUG (char *, case_str_rw (*c, vr)),
+                         var_get_width (vr));
     }
 
   return TRNS_CONTINUE;
diff --git a/src/language/xforms/recode.c b/src/language/xforms/recode.c
index 424e0af..fff74f7 100644
--- a/src/language/xforms/recode.c
+++ b/src/language/xforms/recode.c
@@ -1,5 +1,5 @@
 /* PSPP - a program for statistical analysis.
-   Copyright (C) 1997-9, 2000, 2009 Free Software Foundation, Inc.
+   Copyright (C) 1997-9, 2000, 2009, 2010 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -373,7 +373,8 @@ set_map_in_str (struct map_in *in, struct pool *pool,
   in->type = MAP_SINGLE;
   value_init_pool (pool, &in->x, width);
   value_copy_buf_rpad (&in->x, width,
-                       ds_data (string), ds_length (string), ' ');
+                       CHAR_CAST_BUG (uint8_t *, ds_data (string)),
+                       ds_length (string), ' ');
 }
 
 /* Parses a mapping output value into OUT, allocating memory from
@@ -629,8 +630,9 @@ find_src_string (struct recode_trns *trns, const uint8_t 
*value,
             union value uv;
 
             msg_disable ();
-            match = data_in (ss_buffer (value, width), LEGACY_NATIVE,
-                             FMT_F, 0, 0, 0, trns->dst_dict,  &uv, 0);
+            match = data_in (ss_buffer (CHAR_CAST_BUG (char *, value), width),
+                             LEGACY_NATIVE, FMT_F, 0, 0, 0, trns->dst_dict,
+                             &uv, 0);
             msg_enable ();
             out->value.f = uv.f;
             break;
diff --git a/src/libpspp/cast.h b/src/libpspp/cast.h
index 1e33857..5c64fac 100644
--- a/src/libpspp/cast.h
+++ b/src/libpspp/cast.h
@@ -1,5 +1,5 @@
 /* PSPP - a program for statistical analysis.
-   Copyright (C) 2009 Free Software Foundation, Inc.
+   Copyright (C) 2009, 2010 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -18,6 +18,7 @@
 #define LIBPSPP_CAST_H 1
 
 #include <stddef.h>
+#include "gl/verify.h"
 
 /* Expands to a void expression that checks that POINTER is an
    expression whose type is a qualified or unqualified version of
@@ -83,6 +84,28 @@
         (CHECK_POINTER_HAS_TYPE (POINTER, TYPE),        \
          (TYPE) (POINTER))
 
+/* Casts POINTER to TYPE.  Yields a compiler diagnostic if either TYPE or
+   POINTER is not a pointer to character type.
+
+   PSPP uses "unsigned char" (actually uint8_t) in "union value" and "char"
+   elsewhere to emphasize that data in union value usually requires reencoding
+   when transferred to and from other string types.  These macros suppress the
+   warning when implicitly converting between pointers to different character
+   types, so their use normally marks a bug that should eventually be fixed.
+   However, until these bugs are fixed, suppressing the warnings is much less
+   annoying.
+
+   Use CHAR_CAST_BUG if you think there is a bug to be fixed, or if you have
+   not yet carefully examined the situation, or if you are not sure.
+   Use CHAR_CAST if you are convinced that this is actually a correct cast. */
+#define CHAR_CAST(TYPE, POINTER)                                \
+        ((void) verify_true (sizeof (*(POINTER)) == 1),         \
+         (void) (sizeof (*(POINTER) + 1)),                      \
+         (void) verify_true (sizeof (*(TYPE) NULL) == 1),       \
+         (void) (sizeof (*(TYPE) NULL + 1)),                    \
+         (TYPE) (POINTER))
+#define CHAR_CAST_BUG(TYPE, POINTER) CHAR_CAST(TYPE, POINTER)
+
 /* Given POINTER, a pointer to the given MEMBER within structure
    STRUCT, returns the address of the STRUCT. */
 #define UP_CAST(POINTER, STRUCT, MEMBER)                                \
diff --git a/src/ui/syntax-gen.c b/src/ui/syntax-gen.c
index 22e717a..229e478 100644
--- a/src/ui/syntax-gen.c
+++ b/src/ui/syntax-gen.c
@@ -1,5 +1,5 @@
 /* PSPPIRE - a graphical user interface for PSPP.
-   Copyright (C) 2008 Free Software Foundation, Inc.
+   Copyright (C) 2008, 2010 Free Software Foundation, Inc.
 
    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -21,13 +21,14 @@
 #include <ctype.h>
 #include <mbchar.h>
 
-#include <data/data-in.h>
-#include <data/data-out.h>
-#include <data/format.h>
-#include <data/value.h>
-#include <libpspp/assertion.h>
-#include <libpspp/message.h>
-#include <libpspp/str.h>
+#include "data/data-in.h"
+#include "data/data-out.h"
+#include "data/format.h"
+#include "data/value.h"
+#include "libpspp/assertion.h"
+#include "libpspp/cast.h"
+#include "libpspp/message.h"
+#include "libpspp/str.h"
 
 /* Appends to OUTPUT a pair of hex digits for each byte in IN. */
 static void
@@ -197,7 +198,10 @@ syntax_gen_value (struct string *output, const union value 
*value, int width,
   if (width == 0)
     syntax_gen_number (output, value->f, format);
   else
-    syntax_gen_string (output, ss_buffer (value_str (value, width), width));
+    {
+      char *s = CHAR_CAST_BUG (char *, value_str (value, width));
+      syntax_gen_string (output, ss_buffer (s, width));
+    }
 }
 
 /* Appends <low> THRU <high> to OUTPUT.  If LOW is LOWEST, then
-- 
1.7.1