Update from gnulib

This incorporates:
2020-05-11 careadlinkat: fix GCC 10 workaround
2020-05-10 careadlinkat: limit GCC workaround
2020-05-10 attribute: clarify list of attributes
2020-05-10 string: fix compilation error in C++ mode
2020-05-09 manywarnings: port to GCC 10.1
2020-05-09 careadlinkat: pacify -Wreturn-local-addr
2020-05-09 attribute: remove ATTRIBUTE_DEPRECATED
2020-05-09 attribute: Add comments
* lib/attribute.h, lib/careadlinkat.c, lib/string.in.h:
* lib/warn-on-use.h, m4/manywarnings.m4: Copy from Gnulib.

4 files changed, 234 insertions, 54 deletions

diff --git a/lib/attribute.h b/lib/attribute.h
index c5919d97005..2836b99dad0 100644
--- a/lib/attribute.h
+++ b/lib/attribute.h
@@ -20,39 +20,196 @@
 /* Provide public ATTRIBUTE_* names for the private _GL_ATTRIBUTE_*
    macros used within Gnulib.  */
 
+/* These attributes can be placed in two ways:
+     - At the start of a declaration (i.e. even before storage-class
+       specifiers!); then they apply to all entities that are declared
+       by the declaration.
+     - Immediately after the name of an entity being declared by the
+       declaration; then they apply to that entity only.  */
+
 #ifndef _GL_ATTRIBUTE_H
 #define _GL_ATTRIBUTE_H
 
-/* C2X standard attributes have macro names that do not begin with
-   'ATTRIBUTE_'.  */
+
+/* This file defines two types of attributes:
+   * C2X standard attributes.  These have macro names that do not begin with
+     'ATTRIBUTE_'.
+   * Selected GCC attributes; see:
+     https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
+     https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html
+     https://gcc.gnu.org/onlinedocs/gcc/Common-Type-Attributes.html
+     These names begin with 'ATTRIBUTE_' to avoid name clashes.  */
+
+
+/* =============== Attributes for specific kinds of functions =============== */
+
+/* Attributes for functions that should not be used.  */
+
+/* Warn if the entity is used.  */
+/* Applies to:
+     - function, variable,
+     - struct, union, struct/union member,
+     - enumeration, enumeration item,
+     - typedef,
+   in C++ also: namespace, class, template specialization.  */
 #define DEPRECATED _GL_ATTRIBUTE_DEPRECATED
-#define FALLTHROUGH _GL_ATTRIBUTE_FALLTHROUGH
-#define MAYBE_UNUSED _GL_ATTRIBUTE_MAYBE_UNUSED
-#define NODISCARD _GL_ATTRIBUTE_NODISCARD
 
-/* Selected GCC attributes; see:
-   https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
-   These names begin with 'ATTRIBUTE_' to avoid name clashes.  */
-#define ATTRIBUTE_ALLOC_SIZE(args) _GL_ATTRIBUTE_ALLOC_SIZE (args)
-#define ATTRIBUTE_ALWAYS_INLINE _GL_ATTRIBUTE_ALWAYS_INLINE
-#define ATTRIBUTE_ARTIFICIAL _GL_ATTRIBUTE_ARTIFICIAL
-#define ATTRIBUTE_COLD _GL_ATTRIBUTE_COLD
-#define ATTRIBUTE_CONST _GL_ATTRIBUTE_CONST
-#define ATTRIBUTE_DEPRECATED _GL_ATTRIBUTE_DEPRECATED
+/* If a function call is not optimized way, warn with MSG.  */
+/* Applies to: functions.  */
+#define ATTRIBUTE_WARNING(msg) _GL_ATTRIBUTE_WARNING (msg)
+
+/* If a function call is not optimized way, report an error with MSG.  */
+/* Applies to: functions.  */
 #define ATTRIBUTE_ERROR(msg) _GL_ATTRIBUTE_ERROR (msg)
-#define ATTRIBUTE_EXTERNALLY_VISIBLE _GL_ATTRIBUTE_EXTERNALLY_VISIBLE
-#define ATTRIBUTE_FORMAT(spec) _GL_ATTRIBUTE_FORMAT (spec)
-#define ATTRIBUTE_LEAF _GL_ATTRIBUTE_LEAF
-#define ATTRIBUTE_MAY_ALIAS _GL_ATTRIBUTE_MAY_ALIAS
+
+
+/* Attributes for memory-allocating functions.  */
+
+/* The function returns a pointer to freshly allocated memory.  */
+/* Applies to: functions.  */
 #define ATTRIBUTE_MALLOC _GL_ATTRIBUTE_MALLOC
-#define ATTRIBUTE_NOINLINE _GL_ATTRIBUTE_NOINLINE
+
+/* ATTRIBUTE_ALLOC_SIZE ((N)) - The Nth argument of the function
+   is the size of the returned memory block.
+   ATTRIBUTE_ALLOC_SIZE ((M, N)) - Multiply the Mth and Nth arguments
+   to determine the size of the returned memory block.  */
+/* Applies to: function, pointer to function, function types.  */
+#define ATTRIBUTE_ALLOC_SIZE(args) _GL_ATTRIBUTE_ALLOC_SIZE (args)
+
+
+/* Attributes for variadic functions.  */
+
+/* The variadic function expects a trailing NULL argument.
+   ATTRIBUTE_SENTINEL () - The last argument is NULL.
+   ATTRIBUTE_SENTINEL ((N)) - The (N+1)st argument from the end is NULL.  */
+/* Applies to: functions.  */
+#define ATTRIBUTE_SENTINEL(pos) _GL_ATTRIBUTE_SENTINEL (pos)
+
+
+/* ================== Attributes for compiler diagnostics ================== */
+
+/* Attributes that help the compiler diagnose programmer mistakes.
+   Some of them may also help for some compiler optimizations.  */
+
+/* ATTRIBUTE_FORMAT ((ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)) -
+   The STRING-INDEXth function argument is a format string of style
+   ARCHETYPE, which is one of:
+     printf, gnu_printf
+     scanf, gnu_scanf,
+     strftime, gnu_strftime,
+     strfmon,
+   or the same thing prefixed and suffixed with '__'.
+   If FIRST-TO-CHECK is not 0, arguments starting at FIRST-TO_CHECK
+   are suitable for the format string.  */
+/* Applies to: functions.  */
+#define ATTRIBUTE_FORMAT(spec) _GL_ATTRIBUTE_FORMAT (spec)
+
+/* ATTRIBUTE_NONNULL ((N1, N2,...)) - Arguments N1, N2,... must not be NULL.
+   ATTRIBUTE_NONNULL () - All pointer arguments must not be null.  */
+/* Applies to: functions.  */
 #define ATTRIBUTE_NONNULL(args) _GL_ATTRIBUTE_NONNULL (args)
+
+/* The function's return value is a non-NULL pointer.  */
+/* Applies to: functions.  */
+#define ATTRIBUTE_RETURNS_NONNULL _GL_ATTRIBUTE_RETURNS_NONNULL
+
+/* Warn if the caller does not use the return value,
+   unless the caller uses something like ignore_value.  */
+/* Applies to: function, enumeration, class.  */
+#define NODISCARD _GL_ATTRIBUTE_NODISCARD
+
+
+/* Attributes that disable false alarms when the compiler diagnoses
+   programmer "mistakes".  */
+
+/* Do not warn if the entity is not used.  */
+/* Applies to:
+     - function, variable,
+     - struct, union, struct/union member,
+     - enumeration, enumeration item,
+     - typedef,
+   in C++ also: class.  */
+#define MAYBE_UNUSED _GL_ATTRIBUTE_MAYBE_UNUSED
+
+/* The contents of a character array is not meant to be NUL-terminated.  */
+/* Applies to: struct/union members and variables that are arrays of element
+   type '[[un]signed] char'.  */
 #define ATTRIBUTE_NONSTRING _GL_ATTRIBUTE_NONSTRING
+
+/* Do not warn if control flow falls through to the immediately
+   following 'case' or 'default' label.  */
+/* Applies to: Empty statement (;), inside a 'switch' statement.  */
+#define FALLTHROUGH _GL_ATTRIBUTE_FALLTHROUGH
+
+
+/* ================== Attributes for debugging information ================== */
+
+/* Attributes regarding debugging information emitted by the compiler.  */
+
+/* Omit the function from stack traces when debugging.  */
+/* Applies to: function.  */
+#define ATTRIBUTE_ARTIFICIAL _GL_ATTRIBUTE_ARTIFICIAL
+
+/* Make the entity visible to debuggers etc., even with '-fwhole-program'.  */
+/* Applies to: functions, variables.  */
+#define ATTRIBUTE_EXTERNALLY_VISIBLE _GL_ATTRIBUTE_EXTERNALLY_VISIBLE
+
+
+/* ========== Attributes that mainly direct compiler optimizations ========== */
+
+/* The function does not throw exceptions.  */
+/* Applies to: functions.  */
 #define ATTRIBUTE_NOTHROW _GL_ATTRIBUTE_NOTHROW
-#define ATTRIBUTE_PACKED _GL_ATTRIBUTE_PACKED
+
+/* Do not inline the function.  */
+/* Applies to: functions.  */
+#define ATTRIBUTE_NOINLINE _GL_ATTRIBUTE_NOINLINE
+
+/* Always inline the function, and report an error if the compiler
+   cannot inline.  */
+/* Applies to: function.  */
+#define ATTRIBUTE_ALWAYS_INLINE _GL_ATTRIBUTE_ALWAYS_INLINE
+
+/* The function does not affect observable state, and always returns a value.
+   Compilers can omit duplicate calls with the same arguments if
+   observable state is not changed between calls.  (This attribute is
+   looser than ATTRIBUTE_CONST.)  */
+/* Applies to: functions.  */
 #define ATTRIBUTE_PURE _GL_ATTRIBUTE_PURE
-#define ATTRIBUTE_RETURNS_NONNULL _GL_ATTRIBUTE_RETURNS_NONNULL
-#define ATTRIBUTE_SENTINEL(pos) _GL_ATTRIBUTE_SENTINEL (pos)
-#define ATTRIBUTE_WARNING(msg) _GL_ATTRIBUTE_WARNING (msg)
+
+/* The function neither depends on nor affects observable state,
+   and always returns a value.  Compilers can omit duplicate calls with
+   the same arguments.  (This attribute is stricter than ATTRIBUTE_PURE.)  */
+/* Applies to: functions.  */
+#define ATTRIBUTE_CONST _GL_ATTRIBUTE_CONST
+
+/* The function is rarely executed.  */
+/* Applies to: functions.  */
+#define ATTRIBUTE_COLD _GL_ATTRIBUTE_COLD
+
+/* If called from some other compilation unit, the function executes
+   code from that unit only by return or by exception handling,
+   letting the compiler optimize that unit more aggressively.  */
+/* Applies to: functions.  */
+#define ATTRIBUTE_LEAF _GL_ATTRIBUTE_LEAF
+
+/* For struct members: The member has the smallest possible alignment.
+   For struct, union, class: All members have the smallest possible alignment,
+   minimizing the memory required.  */
+/* Applies to: struct members, struct, union,
+   in C++ also: class.  */
+#define ATTRIBUTE_PACKED _GL_ATTRIBUTE_PACKED
+
+
+/* ================ Attributes that make invalid code valid ================ */
+
+/* Attributes that prevent fatal compiler optimizations for code that is not
+   fully ISO C compliant.  */
+
+/* Pointers to the type may point to the same storage as pointers to
+   other types, thus disabling strict aliasing optimization.  */
+/* Applies to: types.  */
+#define ATTRIBUTE_MAY_ALIAS _GL_ATTRIBUTE_MAY_ALIAS
+
 
 #endif /* _GL_ATTRIBUTE_H */
diff --git a/lib/careadlinkat.c b/lib/careadlinkat.c
index 1effdb78451..1aa04363dac 100644
--- a/lib/careadlinkat.c
+++ b/lib/careadlinkat.c
@@ -72,23 +72,38 @@ careadlinkat (int fd, char const *filename,
     SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX;
   char stack_buf[1024];
 
+#if (defined GCC_LINT || defined lint) && _GL_GNUC_PREREQ (10, 1)
+  /* Pacify preadlinkat without creating a pointer to the stack
+     that a broken gcc -Wreturn-local-addr would cry wolf about.  See:
+     https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95044
+     This workaround differs from the mainline code, but
+     no other way to pacify GCC 10.1.0 is known; even an explicit
+     #pragma does not pacify GCC.  When the GCC bug is fixed this
+     workaround should be limited to the broken GCC versions.  */
+# define WORK_AROUND_GCC_BUG_95044
+#endif
+
   if (! alloc)
     alloc = &stdlib_allocator;
 
-  if (! buffer_size)
+  if (!buffer)
     {
+#ifdef WORK_AROUND_GCC_BUG_95044
+      buffer = alloc->allocate (sizeof stack_buf);
+#else
       /* Allocate the initial buffer on the stack.  This way, in the
          common case of a symlink of small size, we get away with a
          single small malloc() instead of a big malloc() followed by a
          shrinking realloc().  */
       buffer = stack_buf;
+#endif
       buffer_size = sizeof stack_buf;
     }
 
   buf = buffer;
   buf_size = buffer_size;
 
-  do
+  while (buf)
     {
       /* Attempt to read the link into the current buffer.  */
       ssize_t link_length = preadlinkat (fd, filename, buf, buf_size);
@@ -117,19 +132,19 @@ careadlinkat (int fd, char const *filename,
 
           if (buf == stack_buf)
             {
-              char *b = (char *) alloc->allocate (link_size);
+              char *b = alloc->allocate (link_size);
               buf_size = link_size;
               if (! b)
                 break;
-              memcpy (b, buf, link_size);
-              buf = b;
+              return memcpy (b, buf, link_size);
             }
-          else if (link_size < buf_size && buf != buffer && alloc->reallocate)
+
+          if (link_size < buf_size && buf != buffer && alloc->reallocate)
             {
               /* Shrink BUF before returning it.  */
-              char *b = (char *) alloc->reallocate (buf, link_size);
+              char *b = alloc->reallocate (buf, link_size);
               if (b)
-                buf = b;
+                return b;
             }
 
           return buf;
@@ -138,8 +153,8 @@ careadlinkat (int fd, char const *filename,
       if (buf != buffer)
         alloc->free (buf);
 
-      if (buf_size <= buf_size_max / 2)
-        buf_size *= 2;
+      if (buf_size < buf_size_max / 2)
+        buf_size = 2 * buf_size + 1;
       else if (buf_size < buf_size_max)
         buf_size = buf_size_max;
       else if (buf_size_max < SIZE_MAX)
@@ -149,9 +164,8 @@ careadlinkat (int fd, char const *filename,
         }
       else
         break;
-      buf = (char *) alloc->allocate (buf_size);
+      buf = alloc->allocate (buf_size);
     }
-  while (buf);
 
   if (alloc->die)
     alloc->die (buf_size);
diff --git a/lib/string.in.h b/lib/string.in.h
index 96e132f37d7..a08e7057fbd 100644
--- a/lib/string.in.h
+++ b/lib/string.in.h
@@ -334,9 +334,10 @@ _GL_WARN_ON_USE (stpncpy, "stpncpy is unportable - "
    GB18030 and the character to be searched is a digit.  */
 # undef strchr
 /* Assume strchr is always declared.  */
-_GL_WARN_ON_USE (strchr, "strchr cannot work correctly on character strings "
-                 "in some multibyte locales - "
-                 "use mbschr if you care about internationalization");
+_GL_WARN_ON_USE_CXX (strchr, const char *, (const char *, int),
+                     "strchr cannot work correctly on character strings "
+                     "in some multibyte locales - "
+                     "use mbschr if you care about internationalization");
 #endif
 
 /* Find the first occurrence of C in S or the final NUL byte.  */
@@ -528,15 +529,17 @@ _GL_CXXALIASWARN (strpbrk);
    locale encoding is GB18030 and one of the characters to be searched is a
    digit.  */
 #  undef strpbrk
-_GL_WARN_ON_USE (strpbrk, "strpbrk cannot work correctly on character strings "
-                 "in multibyte locales - "
-                 "use mbspbrk if you care about internationalization");
+_GL_WARN_ON_USE_CXX (strpbrk, const char *, (const char *, const char *),
+                     "strpbrk cannot work correctly on character strings "
+                     "in multibyte locales - "
+                     "use mbspbrk if you care about internationalization");
 # endif
 #elif defined GNULIB_POSIXCHECK
 # undef strpbrk
 # if HAVE_RAW_DECL_STRPBRK
-_GL_WARN_ON_USE (strpbrk, "strpbrk is unportable - "
-                 "use gnulib module strpbrk for portability");
+_GL_WARN_ON_USE_CXX (strpbrk, const char *, (const char *, const char *),
+                     "strpbrk is unportable - "
+                     "use gnulib module strpbrk for portability");
 # endif
 #endif
 
@@ -555,9 +558,10 @@ _GL_WARN_ON_USE (strspn, "strspn cannot work correctly on character strings "
    GB18030 and the character to be searched is a digit.  */
 # undef strrchr
 /* Assume strrchr is always declared.  */
-_GL_WARN_ON_USE (strrchr, "strrchr cannot work correctly on character strings "
-                 "in some multibyte locales - "
-                 "use mbsrchr if you care about internationalization");
+_GL_WARN_ON_USE_CXX (strrchr, const char *, (const char *, int),
+                     "strrchr cannot work correctly on character strings "
+                     "in some multibyte locales - "
+                     "use mbsrchr if you care about internationalization");
 #endif
 
 /* Search the next delimiter (char listed in DELIM) starting at *STRINGP.
diff --git a/lib/warn-on-use.h b/lib/warn-on-use.h
index 1be2cbb9570..23c10fdd122 100644
--- a/lib/warn-on-use.h
+++ b/lib/warn-on-use.h
@@ -100,23 +100,28 @@ _GL_WARN_EXTERN_C int _gl_warn_on_use
 #endif
 
 /* _GL_WARN_ON_USE_CXX (function, rettype, parameters_and_attributes, "string")
-   is like _GL_WARN_ON_USE (function, "string"), except that the function is
-   declared with the given prototype, consisting of return type, parameters,
-   and attributes.
+   is like _GL_WARN_ON_USE (function, "string"), except that in C++ mode the
+   function is declared with the given prototype, consisting of return type,
+   parameters, and attributes.
    This variant is useful for overloaded functions in C++. _GL_WARN_ON_USE does
    not work in this case.  */
 #ifndef _GL_WARN_ON_USE_CXX
-# if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
+# if !defined __cplusplus
 #  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
+     _GL_WARN_ON_USE (function, msg)
+# else
+#  if 4 < __GNUC__ || (__GNUC__ == 4 && 3 <= __GNUC_MINOR__)
+#   define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
 extern rettype function parameters_and_attributes \
      __attribute__ ((__warning__ (msg)))
-# elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
+#  elif __GNUC__ >= 3 && GNULIB_STRICT_CHECKING
 /* Verify the existence of the function.  */
-#  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
+#   define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
 extern rettype function parameters_and_attributes
-# else /* Unsupported.  */
-#  define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
+#  else /* Unsupported.  */
+#   define _GL_WARN_ON_USE_CXX(function,rettype,parameters_and_attributes,msg) \
 _GL_WARN_EXTERN_C int _gl_warn_on_use
+#  endif
 # endif
 #endif