join: with --check-order print offending file name, line number and data

* src/join (g_names): New global (was main's "names").
(main): Update all uses of "names".
(line_no[2]): New globals.
(get_line): Increment after reading each line.
(check_order): Print the standard "file name:line_no: " prefix
as well as the offending line when reporting disorder.
Here is a sample old/new comparison:
  -join: file 1 is not in sorted order
  +join: in:4: is not sorted: contents-of-line-4
* tests/misc/join: Change the two affected tests to expect
the new diagnostic.
Add new tests for more coverage: mismatch in file 2,
two diagnostics, zero-length out-of-order line.
* NEWS (Improvements): Mention it.
Suggested by David Gast in http://debbugs.gnu.org/9236

1 files changed, 30 insertions, 13 deletions

diff --git a/src/join.c b/src/join.c
index 99d918fd1..694fb5573 100644
--- a/src/join.c
+++ b/src/join.c
@@ -86,9 +86,15 @@ struct seq
     struct line **lines;
   };
 
-/* The previous line read from each file. */
+/* The previous line read from each file.  */
 static struct line *prevline[2] = {NULL, NULL};
 
+/* The number of lines read from each file.  */
+static uintmax_t line_no[2] = {0, 0};
+
+/* The input file names.  */
+static char *g_names[2];
+
 /* This provides an extra line buffer for each file.  We need these if we
    try to read two consecutive lines into the same buffer, since we don't
    want to overwrite the previous buffer before we check order. */
@@ -384,12 +390,23 @@ check_order (const struct line *prev,
           size_t join_field = whatfile == 1 ? join_field_1 : join_field_2;
           if (keycmp (prev, current, join_field, join_field) > 0)
             {
+              /* Exclude any trailing newline. */
+              size_t len = current->buf.length;
+              if (0 < len && current->buf.buffer[len - 1] == '\n')
+                --len;
+
+              /* If the offending line is longer than INT_MAX, output
+                 only the first INT_MAX bytes in this diagnostic.  */
+              len = MIN (INT_MAX, len);
+
               error ((check_input_order == CHECK_ORDER_ENABLED
                       ? EXIT_FAILURE : 0),
-                     0, _("file %d is not in sorted order"), whatfile);
+                     0, _("%s:%ju: is not sorted: %.*s"),
+                     g_names[whatfile - 1], line_no[whatfile - 1],
+                     (int) len, current->buf.buffer);
 
-              /* If we get to here, the message was just a warning, but we
-                 want only to issue it once. */
+              /* If we get to here, the message was merely a warning.
+                 Arrange to issue it only once per file.  */
               issued_disorder_warning[whatfile-1] = true;
             }
         }
@@ -436,6 +453,7 @@ get_line (FILE *fp, struct line **linep, int which)
       freeline (line);
       return false;
     }
+  ++line_no[which - 1];
 
   xfields (line);
 
@@ -980,7 +998,6 @@ main (int argc, char **argv)
   int prev_optc_status = MUST_BE_OPERAND;
   int operand_status[2];
   int joption_count[2] = { 0, 0 };
-  char *names[2];
   FILE *fp1, *fp2;
   int optc;
   int nfiles = 0;
@@ -1100,7 +1117,7 @@ main (int argc, char **argv)
           break;
 
         case 1:		/* Non-option argument.  */
-          add_file_name (optarg, names, operand_status, joption_count,
+          add_file_name (optarg, g_names, operand_status, joption_count,
                          &nfiles, &prev_optc_status, &optc_status);
           break;
 
@@ -1122,7 +1139,7 @@ main (int argc, char **argv)
   /* Process any operands after "--".  */
   prev_optc_status = MUST_BE_OPERAND;
   while (optind < argc)
-    add_file_name (argv[optind++], names, operand_status, joption_count,
+    add_file_name (argv[optind++], g_names, operand_status, joption_count,
                    &nfiles, &prev_optc_status, &optc_status);
 
   if (nfiles != 2)
@@ -1148,20 +1165,20 @@ main (int argc, char **argv)
   if (join_field_2 == SIZE_MAX)
     join_field_2 = 0;
 
-  fp1 = STREQ (names[0], "-") ? stdin : fopen (names[0], "r");
+  fp1 = STREQ (g_names[0], "-") ? stdin : fopen (g_names[0], "r");
   if (!fp1)
-    error (EXIT_FAILURE, errno, "%s", names[0]);
-  fp2 = STREQ (names[1], "-") ? stdin : fopen (names[1], "r");
+    error (EXIT_FAILURE, errno, "%s", g_names[0]);
+  fp2 = STREQ (g_names[1], "-") ? stdin : fopen (g_names[1], "r");
   if (!fp2)
-    error (EXIT_FAILURE, errno, "%s", names[1]);
+    error (EXIT_FAILURE, errno, "%s", g_names[1]);
   if (fp1 == fp2)
     error (EXIT_FAILURE, errno, _("both files cannot be standard input"));
   join (fp1, fp2);
 
   if (fclose (fp1) != 0)
-    error (EXIT_FAILURE, errno, "%s", names[0]);
+    error (EXIT_FAILURE, errno, "%s", g_names[0]);
   if (fclose (fp2) != 0)
-    error (EXIT_FAILURE, errno, "%s", names[1]);
+    error (EXIT_FAILURE, errno, "%s", g_names[1]);
 
   if (issued_disorder_warning[0] || issued_disorder_warning[1])
     exit (EXIT_FAILURE);