notmuch: Support "notmuch part" as an alias for "notmuch show --format=raw"

We unifed the "notmuch part" functionality into "notmuch show" where
the implementation is both simpler and more powerful. But there's no
good reason to break users of the old interface.

Add support for aliases, which are undocumented means of getting at
functionality through deprecated names. The first such alias is
"notmuch part" as implemented here.

notmuch.c

@@ -32,6 +32,17 @@ typedef struct command {
     const char *documentation;
 } command_t;
 
+#define MAX_ALIAS_SUBSTITUTIONS 2
+
+typedef struct alias {
+    const char *name;
+    const char *substitutions[MAX_ALIAS_SUBSTITUTIONS];
+} alias_t;
+
+alias_t aliases[] = {
+    { "part", { "show", "--format=raw"}}
+};
+
 static int
 notmuch_help_command (void *ctx, int argc, char *argv[]);
 
@@ -115,7 +126,7 @@ static const char search_terms_help[] =
     "\n"
     "\t\t$(date +%%s -d 2009-10-01)..$(date +%%s)\n\n";
 
-command_t commands[] = {
+static command_t commands[] = {
     { "setup", notmuch_setup_command,
       NULL,
       "Interactively setup notmuch for first use.",
@@ -546,7 +557,9 @@ main (int argc, char *argv[])
 {
     void *local;
     command_t *command;
-    unsigned int i;
+    alias_t *alias;
+    unsigned int i, j;
+    const char **argv_local;
 
     talloc_enable_null_tracking ();
 
@@ -565,6 +578,40 @@ main (int argc, char *argv[])
 	return 0;
     }
 
+    for (i = 0; i < ARRAY_SIZE (aliases); i++) {
+	alias = &aliases[i];
+
+	if (strcmp (argv[1], alias->name) == 0)
+	{
+	    int substitutions;
+
+	    argv_local = talloc_size (local, sizeof (char *) *
+				      (argc + MAX_ALIAS_SUBSTITUTIONS - 1));
+	    if (argv_local == NULL) {
+		fprintf (stderr, "Out of memory.\n");
+		return 1;
+	    }
+
+	    /* Copy all substution arguments from the alias. */
+	    argv_local[0] = argv[0];
+	    for (j = 0; j < MAX_ALIAS_SUBSTITUTIONS; j++) {
+		if (alias->substitutions[j] == NULL)
+		    break;
+		argv_local[j+1] = alias->substitutions[j];
+	    }
+	    substitutions = j;
+
+	    /* And copy all original arguments (skipping the argument
+	     * that matched the alias of course. */
+	    for (j = 2; j < (unsigned) argc; j++) {
+		argv_local[substitutions+j-1] = argv[j];
+	    }
+
+	    argc += substitutions - 1;
+	    argv = (char **) argv_local;
+	}
+    }
+
     for (i = 0; i < ARRAY_SIZE (commands); i++) {
 	command = &commands[i];