fast-import: prevent producing bad delta

diff --git a/help.c b/help.c
index 7f4928e45954465d0401964289952aec4bd59e2a..7654f1bfd608d151a213937614449cc497bb638b 100644 (file)
--- a/help.c
+++ b/help.c
@@ -3,6 +3,7 @@
 #include "exec_cmd.h"
 #include "levenshtein.h"
 #include "help.h"
+#include "common-cmds.h"
 
 /* most GUI terminals set COLUMNS (although some don't export it) */
 static int term_columns(void)
@@ -298,7 +299,8 @@ static void add_cmd_list(struct cmdnames *cmds, struct cmdnames *old)
 }
 
 /* An empirically derived magic number */
-#define SIMILAR_ENOUGH(x) ((x) < 6)
+#define SIMILARITY_FLOOR 7
+#define SIMILAR_ENOUGH(x) ((x) < SIMILARITY_FLOOR)
 
 const char *help_unknown_cmd(const char *cmd)
 {
@@ -319,10 +321,28 @@ const char *help_unknown_cmd(const char *cmd)
              sizeof(main_cmds.names), cmdname_compare);
        uniq(&main_cmds);
 
-       /* This reuses cmdname->len for similarity index */
-       for (i = 0; i < main_cmds.cnt; ++i)
+       /* This abuses cmdname->len for levenshtein distance */
+       for (i = 0, n = 0; i < main_cmds.cnt; i++) {
+               int cmp = 0; /* avoid compiler stupidity */
+               const char *candidate = main_cmds.names[i]->name;
+
+               /* Does the candidate appear in common_cmds list? */
+               while (n < ARRAY_SIZE(common_cmds) &&
+                      (cmp = strcmp(common_cmds[n].name, candidate)) < 0)
+                       n++;
+               if ((n < ARRAY_SIZE(common_cmds)) && !cmp) {
+                       /* Yes, this is one of the common commands */
+                       n++; /* use the entry from common_cmds[] */
+                       if (!prefixcmp(candidate, cmd)) {
+                               /* Give prefix match a very good score */
+                               main_cmds.names[i]->len = 0;
+                               continue;
+                       }
+               }
+
                main_cmds.names[i]->len =
-                       levenshtein(cmd, main_cmds.names[i]->name, 0, 2, 1, 4);
+                       levenshtein(cmd, candidate, 0, 2, 1, 4) + 1;
+       }
 
        qsort(main_cmds.names, main_cmds.cnt,
              sizeof(*main_cmds.names), levenshtein_compare);
@@ -330,10 +350,21 @@ const char *help_unknown_cmd(const char *cmd)
        if (!main_cmds.cnt)
                die ("Uh oh. Your system reports no Git commands at all.");
 
-       best_similarity = main_cmds.names[0]->len;
-       n = 1;
-       while (n < main_cmds.cnt && best_similarity == main_cmds.names[n]->len)
-               ++n;
+       /* skip and count prefix matches */
+       for (n = 0; n < main_cmds.cnt && !main_cmds.names[n]->len; n++)
+               ; /* still counting */
+
+       if (main_cmds.cnt <= n) {
+               /* prefix matches with everything? that is too ambiguous */
+               best_similarity = SIMILARITY_FLOOR + 1;
+       } else {
+               /* count all the most similar ones */
+               for (best_similarity = main_cmds.names[n++]->len;
+                    (n < main_cmds.cnt &&
+                     best_similarity == main_cmds.names[n]->len);
+                    n++)
+                       ; /* still counting */
+       }
        if (autocorrect && n == 1 && SIMILAR_ENOUGH(best_similarity)) {
                const char *assumed = main_cmds.names[0]->name;
                main_cmds.names[0] = NULL;