argmatch: accept perfect matches in documented arglists

[Akim Demaille]

Bison has been using for years a trick with argmatch: exploit
the support for partial matches to have a simple documentation
system:

$ bison --trace=help
bison: invalid argument ‘help’ for ‘--trace’
Valid arguments are:
  - ‘none        - no traces’
  - ‘scan        - grammar scanner traces’
  - ‘parse       - grammar parser traces’
  - ‘parse-stats - grammar parser stats’
  - ‘automaton   - construction of the automaton’
  - ‘bitsets     - use of bitsets’
  - ‘closure     - input/output of closure’
  - ‘grammar     - reading, reducing the grammar’
  - ‘resource    - memory consumption (where available)’
  - ‘sets        - grammar sets: firsts, nullable etc.’
  - ‘muscles     - m4 definitions passed to the skeleton’
  - ‘tools       - m4 invocation’
  - ‘m4          - m4 traces’
  - ‘skeleton    - skeleton postprocessing’
  - ‘time        - time consumption’
  - ‘ielr        - IELR conversion’
  - ‘all         - all of the above’

This is a low profile feature, meant for Bison developers and
contributors, not end users, so i18n is not an issue here.

However, I just introduced the parse-stats category, and as a
consequence "--trace=parse" no longer matches the corresponding
item, since "parse" is a prefix for both
"parse       - grammar parser traces" and
"parse-stats - grammar parser stats".

I don't think people are using arguments with spaces, so I propose
to acknowledge this use of argmatch by accepting as a perfect match
the first option, since "parse" is a prefix followed by a space.

WDYT?


commit 7fc1d6af473b6572bc643e0481ac0e04f9150cd1
Author: Akim Demaille <address@hidden>
Date:   Thu Apr 18 22:48:29 2019 +0200

    argmatch: accept perfect matches in documented arglists
    
    * lib/argmatch.c (argmatch): Consider effective arguments that are
    prefix of one of the arglist followed by a space to be perfect
    matches.

diff --git a/ChangeLog b/ChangeLog
index 7d6cb0b0a..0ce1de17d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2019-04-18  Akim Demaille  <address@hidden>
+
+       argmatch: accept perfect matches in documented arglists.
+       * lib/argmatch.c (argmatch): Consider effective arguments that are
+       prefix of one of the arglist followed by a space to be perfect
+       matches.
+
 2019-04-18  Akim Demaille  <address@hidden>
 
        argmatch: use void* for raw memory pointers
diff --git a/lib/argmatch.c b/lib/argmatch.c
index 7666ef414..79512125c 100644
--- a/lib/argmatch.c
+++ b/lib/argmatch.c
@@ -78,7 +78,17 @@ argmatch_exit_fn argmatch_die = __argmatch_die;
    synonyms, i.e., for
      "yes", "yop" -> 0
      "no", "nope" -> 1
-   "y" is a valid argument, for 0, and "n" for 1.  */
+   "y" is a valid argument, for 0, and "n" for 1.
+
+   Accept arguments with a documentation string, such as:
+     "foo - a first feature" -> 0
+     "bar - a second feature" -> 1
+     "barest - a better second feature" -> 2
+   In this case, "ba" is ambiguous, but accept "bar" as a perfect
+   match of 1, even though technically it is also a prefix for 2.
+   This is because "bar" is followed by a space in the argument list
+   ("bar - a second feature").
+  */
 
 ptrdiff_t
 argmatch (const char *arg, const char *const *arglist,
@@ -96,7 +106,8 @@ argmatch (const char *arg, const char *const *arglist,
     {
       if (!strncmp (arglist[i], arg, arglen))
         {
-          if (strlen (arglist[i]) == arglen)
+          if (strlen (arglist[i]) == arglen
+              || (arglen < strlen (arglist[i]) && arglist[i][arglen] == ' '))
             /* Exact match found.  */
             return i;
           else if (matchind == -1)