Re: [PATCH v2 2/3] parse-options: add early_scan_options()

diff --git a/parse-options.c b/parse-options.c
index a132c1ea12..559dad9061 100644
--- a/parse-options.c
+++ b/parse-options.c

[ snip ]

+int early_scan_options(int argc, const char **argv,
+		       const struct option *option,
+		       enum early_scan_flags flags,
+		       early_scan_fn *fn, void *data)
+{
+	for (int i = 0; i < argc; i++) {
+		const char *arg = argv[i];
+		const char *value;
+		const struct option *opt;
+		int pos = i;
+
+		/*
+		 * parse_options() always stops parsing options at these,
+		 * whatever its flags, so nothing after them is an option.
+		 */
+		if (!strcmp(arg, "--") || !strcmp(arg, "--end-of-options"))
+			return i;
+
+		opt = find_early_scan_option(arg, option, &value);
+		if (!opt) {
+			if ((flags & EARLY_SCAN_STOP_AT_NON_OPTION) &&
+			    (*arg != '-' || !arg[1]))
+				return i;
+			continue;
+		}
+
+		/*
+		 * When an option takes a value, but that value is not
+		 * stuck to it with '=', then the next argument is the
+		 * value and it has to be skipped so that it isn't
+		 * taken for an option itself.
+		 */
+		if (parse_options_takes_argument(opt) && !value && i + 1 < argc)
+			value = argv[++i];
+

+		if (opt->flags & PARSE_OPT_EARLY && fn(opt, value, pos, data))
+			return i;
+	}
+
+	return argc;
+}
+
  static int usage_argh(const struct option *opts, FILE *outfile)
  {
  	const char *s;

diff --git a/parse-options.h b/parse-options.h
index f29e73f85c..3ef64744a4 100644
--- a/parse-options.h
+++ b/parse-options.h

[ snip ]

+/*
+ * Scan `argv` for the options described by `option`, calling `fn` for
+ * each of those that have PARSE_OPT_EARLY set. `argv` is not
+ * modified.
+ *
+ * `fn` may be NULL when no option has PARSE_OPT_EARLY set, which is
+ * useful to only find out where the scan stops.
+ *
+ * The scan always stops at "--" and at "--end-of-options", as
+ * parse_options() always stops parsing options there too, whatever its
+ * flags. PARSE_OPT_KEEP_DASHDASH and PARSE_OPT_KEEP_UNKNOWN_OPT only
+ * decide if the terminator is left in argv, not if it terminates.
+ *
+ * Returns the index at which the scan stopped, which is `argc` when the
+ * whole array was scanned.
+ *

+ * This scan is for now deliberately much simpler than
+ * parse_options(), so it differs from it in the following ways:
+ *
+ *  - Only the long form of an option is matched, and it has to be
+ *    spelled in full: short options and abbreviations are ignored.
+ *
+ *  - Negated forms ("--no-<name>") are not matched. This is harmless,
+ *    as they never take a value to skip.
+ *
+ *  - Options with PARSE_OPT_OPTARG or PARSE_OPT_LASTARG_DEFAULT are
+ *    treated as not taking a separate value.
+ *
+ *  - OPTION_SUBCOMMAND entries are skipped.
+ *
+ *  - OPTION_ALIAS entries are not resolved to the option they stand
+ *    for.
+ *
+ * So the scan can fail to see an option that parse_options() would
+ * accept, and callers have to cope with that, typically by erring on
+ * the safe side.
+ */
+int early_scan_options(int argc, const char **argv,
+		       const struct option *option,
+		       enum early_scan_flags flags,
+		       early_scan_fn *fn, void *data);

[ snip ]>

diff --git a/t/t0040-parse-options.sh b/t/t0040-parse-options.sh
index 449fff4d34..b796d96b9a 100755

[ snip ]> +
+test_expect_success 'early_scan_options() takes values from struct option' '
+	test-tool early-scan-options --number --wanted >actual &&
+	cat >expect <<-\EOF &&
+	stopped at: 2 of 2
+	EOF
+	test_cmp expect actual &&
+	test-tool early-scan-options --number=5 --wanted >actual &&
+	cat >expect <<-\EOF &&
+	found: wanted at 1
+	stopped at: 2 of 2
+	EOF
+	test_cmp expect actual
+'

+test_expect_success 'early_scan_options() does not skip an optional value' '
+	test-tool early-scan-options --optarg --wanted >actual &&
+	cat >expect <<-\EOF &&
+	found: wanted at 1
+	stopped at: 2 of 2
+	EOF
+	test_cmp expect actual &&
+	test-tool early-scan-options --lastarg --wanted >actual &&
+	cat >expect <<-\EOF &&
+	found: wanted at 1
+	stopped at: 2 of 2
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'early_scan_options() matches a stuck optional value' '
+	test-tool early-scan-options --early-optarg=one >actual &&
+	cat >expect <<-\EOF &&
+	found: early-optarg at 0 value: one
+	stopped at: 1 of 1
+	EOF
+	test_cmp expect actual &&
+	test-tool early-scan-options --early-lastarg=two >actual &&
+	cat >expect <<-\EOF &&
+	found: early-lastarg at 0 value: two
+	stopped at: 1 of 1
+	EOF
+	test_cmp expect actual
+'