realpath: support the -E option required by POSIX

* src/realpath.c (longopts): Add the option.
(main): Likewise.
(usage): Add the option to the --help message.
* tests/misc/realpath.sh: Add a simple test.
* doc/coreutils.texi (realpath invocation): Mention the new option.
* NEWS: Likewise.

NEWS

@@ -80,6 +80,10 @@ GNU coreutils NEWS                                    -*- outline -*-
   basenc supports the --base58 option to encode and decode
   the visually unambiguous Base58 encoding.
 
+  realpath supports the -E option as required by POSIX.  The behavior is
+  the same as realpath with no options.  The corresponding long option
+  is --canonicalize.
+
 ** Improvements
 
   'factor' is now much faster at identifying large prime numbers,

doc/coreutils.texi

@@ -15006,8 +15006,7 @@ Exit status:
 @findex realpath
 
 @command{realpath} expands all symbolic links and resolves references to
-@samp{/./}, @samp{/../} and extra @samp{/} characters.  By default,
-all but the last component of the specified files must exist.  Synopsis:
+@samp{/./}, @samp{/../} and extra @samp{/} characters.  Synopsis:
 
 @example
 realpath [@var{option}]@dots{} @var{file}@dots{}
@@ -15022,6 +15021,17 @@ The program accepts the following options.  Also see @ref{Common options}.
 
 @table @samp
 
+@item -E
+@itemx --canonicalize
+@opindex -E
+@opindex --canonicalize
+
+Ensure all but the last component of the specified file name exist.
+Otherwise, @command{realpath} will output a diagnostic unless the
+@option{-q} option is specified, and exit with a nonzero exit code.  A
+trailing slash is ignored.  This option is the default behavior, but is
+included for POSIX compatibility.
+
 @item -e
 @itemx --canonicalize-existing
 @opindex -e

src/realpath.c

@@ -44,6 +44,7 @@ static char const *can_relative_base;
 
 static struct option const longopts[] =
 {
+  {"canonicalize", no_argument, nullptr, 'E'},
   {"canonicalize-existing", no_argument, nullptr, 'e'},
   {"canonicalize-missing", no_argument, nullptr, 'm'},
   {"relative-to", required_argument, nullptr, RELATIVE_TO_OPTION},
@@ -68,11 +69,11 @@ usage (int status)
     {
       printf (_("Usage: %s [OPTION]... FILE...\n"), program_name);
       fputs (_("\
-Print the resolved absolute file name;\n\
-all but the last component must exist\n\
-\n\
+Print the resolved absolute file name.\n\
 "), stdout);
       fputs (_("\
+  -E, --canonicalize           all but the last component must exist (default)\
+\n\
   -e, --canonicalize-existing  all components of the path must exist\n\
   -m, --canonicalize-missing   no path components need exist or be a directory\
 \n\
@@ -186,11 +187,15 @@ main (int argc, char **argv)
 
   while (true)
     {
-      int c = getopt_long (argc, argv, "eLmPqsz", longopts, nullptr);
+      int c = getopt_long (argc, argv, "EeLmPqsz", longopts, nullptr);
       if (c == -1)
         break;
       switch (c)
         {
+        case 'E':
+          can_mode &= ~CAN_MODE_MASK;
+          can_mode |= CAN_ALL_BUT_LAST;
+          break;
         case 'e':
           can_mode &= ~CAN_MODE_MASK;
           can_mode |= CAN_EXISTING;

tests/misc/realpath.sh

@@ -50,6 +50,9 @@ returns_ 1 realpath --relative-base . || fail=1
 returns_ 1 realpath -e --relative-to=dir1/f --relative-base=. . || fail=1
 realpath -e --relative-to=dir1/  --relative-base=. . || fail=1
 
+# Check that using -E after -e uses -E as specified by POSIX.
+realpath -e -E --relative-to=dir1/f --relative-base=. . || fail=1
+
 # Note NUL params are unconditionally rejected by canonicalize_filename_mode
 returns_ 1 realpath -m '' || fail=1
 returns_ 1 realpath --relative-base= --relative-to=. . || fail=1