ccanlint: create reduce-feature config.h

A common mistake is not to try compiling with features disabled in
config.h.  The ideal case would determine how features interact and
test all combinations of them: this simply disables any features
mentioned in the code which were previously enabled.

tools/ccanlint/tests/reduce_features.c

+#include <tools/ccanlint/ccanlint.h>
+#include <tools/tools.h>
+#include <ccan/htable/htable_type.h>
+#include <ccan/foreach/foreach.h>
+#include <ccan/talloc/talloc.h>
+#include <ccan/grab_file/grab_file.h>
+#include <ccan/str/str.h>
+#include <ccan/str_talloc/str_talloc.h>
+#include <ccan/hash/hash.h>
+#include <ccan/read_write_all/read_write_all.h>
+#include <errno.h>
+#include <err.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include "reduce_features.h"
+
+bool features_were_reduced;
+
+static const char *can_run(struct manifest *m)
+{
+	if (!config_header)
+		return talloc_strdup(m, "Could not read config.h");
+	return NULL;
+}
+
+static size_t option_hash(const char *name)
+{
+	return hash(name, strlen(name), 0);
+}
+
+static const char *option_name(const char *name)
+{
+	return name;
+}
+
+static bool option_cmp(const char *name1, const char *name2)
+{
+	return streq(name1, name2);
+}
+
+HTABLE_DEFINE_TYPE(char, option_name, option_hash, option_cmp, option);
+
+static unsigned int add_options(struct htable_option *opts,
+				struct pp_conditions *cond)
+{
+	unsigned int num = 0;
+	if (cond->parent)
+		num += add_options(opts, cond->parent);
+	if (cond->type == PP_COND_IF || cond->type == PP_COND_IFDEF) {
+		if (strstarts(cond->symbol, "HAVE_")) {
+			if (!htable_option_get(opts, cond->symbol)) {
+				htable_option_add(opts, cond->symbol);
+				num++;
+			}
+		}
+	}
+	return num;
+}
+
+static struct htable_option *get_used_options(struct manifest *m)
+{
+	struct list_head *list;
+	struct ccan_file *f;
+	unsigned int i, num;
+	struct htable_option *opts = htable_option_new();
+	struct line_info *info;
+
+	num = 0;
+	foreach_ptr(list, &m->c_files, &m->h_files) {
+		list_for_each(list, f, list) {
+			info = get_ccan_line_info(f);
+			struct pp_conditions *prev = NULL;
+
+			for (i = 0; i < f->num_lines; i++) {
+				if (info[i].cond && info[i].cond != prev) {
+					num += add_options(opts, info[i].cond);
+					prev = info[i].cond;
+				}
+			}
+		}
+	}
+
+	if (!num) {
+		htable_option_free(opts);
+		opts = NULL;
+	}
+	return opts;
+}
+
+static struct htable_option *get_config_options(struct manifest *m)
+{
+	const char **lines = (const char **)strsplit(m, config_header, "\n");
+	unsigned int i;
+	struct htable_option *opts = htable_option_new();
+
+	for (i = 0; i < talloc_array_length(lines) - 1; i++) {
+		char *sym;
+
+		if (!get_token(&lines[i], "#"))
+			continue;
+		if (!get_token(&lines[i], "define"))
+			continue;
+		sym = get_symbol_token(lines, &lines[i]);
+		if (!strstarts(sym, "HAVE_"))
+			continue;
+		/* Don't override endian... */
+		if (strends(sym, "_ENDIAN"))
+			continue;
+		if (!get_token(&lines[i], "1"))
+			continue;
+		htable_option_add(opts, sym);
+	}
+	return opts;
+}
+
+static void do_reduce_features(struct manifest *m,
+			       bool keep,
+			       unsigned int *timeleft, struct score *score)
+{
+	struct htable_option *options_used, *options_avail, *options;
+	struct htable_option_iter i;
+	int fd;
+	const char *sym;
+	char *hdr;
+
+	/* This isn't really a test, as such. */
+	score->total = 0;
+	score->pass = true;
+
+	options_used = get_used_options(m);
+	if (!options_used) {
+		return;
+	}
+	options_avail = get_config_options(m);
+
+	options = NULL;
+	for (sym = htable_option_first(options_used, &i);
+	     sym;
+	     sym = htable_option_next(options_used, &i)) {
+		if (htable_option_get(options_avail, sym)) {
+			if (!options)
+				options = htable_option_new();
+			htable_option_add(options, sym);
+		}
+	}
+	htable_option_free(options_avail);
+	htable_option_free(options_used);
+
+	if (!options)
+		return;
+
+	/* Now make our own config.h variant, with our own options. */
+	hdr = talloc_strdup(m, "/* Modified by reduce_features */\n");
+	hdr = talloc_append_string(hdr, config_header);
+	for (sym = htable_option_first(options, &i);
+	     sym;
+	     sym = htable_option_next(options, &i)) {
+		hdr = talloc_asprintf_append
+			(hdr, "#undef %s\n#define %s 0\n", sym, sym);
+	}
+	fd = open("config.h", O_EXCL|O_CREAT|O_RDWR, 0600);
+	if (fd < 0)
+		err(1, "Creating config.h");
+	if (!write_all(fd, hdr, strlen(hdr)))
+		err(1, "Writing config.h");
+	close(fd);
+	features_were_reduced = true;
+}
+
+struct ccanlint reduce_features = {
+	.key = "reduce_features",
+	.name = "Produce config.h with reduced features",
+	.can_run = can_run,
+	.check = do_reduce_features,
+	.needs = "tests_compile"
+};
+REGISTER_TEST(reduce_features);

tools/ccanlint/tests/reduce_features.h

+#ifndef CCANLINT_REDUCE_FEATURES_H
+#define CCANLINT_REDUCE_FEATURES_H
+extern bool features_were_reduced;
+#endif /* CCANLINT_REDUCE_FEATURES_H */