run-command config experiment

This used to take a repo option, but it gets tricky: if we are called
from start_command(), how do we know which repository struct to use?

Instead, this just punts and does not respect in-repo config at all.

Signed-off-by: Jeff King <peff@peff.net>

Author: peff

run-command.c

@@ -680,6 +680,9 @@ int start_command(struct child_process *cmd)
 	int failed_errno;
 	const char *str;
 
+	if (cmd->git_cmd)
+		trace_config_for(NULL, cmd->args.v[0], &cmd->env);
+
 	/*
 	 * In case of errors we must keep the promise to close FDs
 	 * that have been passed in via ->in and ->out.

trace.c

@@ -29,6 +29,8 @@
 #include "quote.h"
 #include "setup.h"
 #include "trace.h"
+#include "strvec.h"
+#include "config.h"
 
 struct trace_key trace_default_key = { "GIT_TRACE", 0, 0, 0 };
 struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
@@ -442,3 +444,47 @@ void trace_command_performance(const char **argv)
 	sq_quote_argv_pretty(&command_line, argv);
 	trace_performance_enter();
 }
+
+struct trace_config_data {
+	const char *want_cmd;
+	struct strvec *out;
+};
+
+static int trace_config_cb(const char *var, const char *value,
+			   const struct config_context *ctx UNUSED, void *vdata)
+{
+	struct trace_config_data *data = vdata;
+	const char *have_cmd, *key;
+	size_t have_len;
+
+	if (!parse_config_key(var, "trace", &have_cmd, &have_len, &key) &&
+	    have_cmd &&
+	    !strncmp(data->want_cmd, have_cmd, have_len) &&
+	    data->want_cmd[have_len] == '\0') {
+		struct strbuf buf = STRBUF_INIT;
+
+		strbuf_addstr(&buf, "GIT_TRACE_");
+		while (*key)
+			strbuf_addch(&buf, toupper(*key++));
+
+		/*
+		 * Environment always takes precedence over config, so do not
+		 * override existing variables. We cannot rely on setenv()'s
+		 * overwrite flag here, because we may pass the list off to
+		 * a spawn() implementation, which always overwrites.
+		 */
+		if (!getenv(buf.buf))
+			strvec_pushf(data->out, "%s=%s", buf.buf, value);
+
+		strbuf_release(&buf);
+	}
+	return 0;
+}
+
+void trace_config_for(struct repository *r, const char *cmd, struct strvec *out)
+{
+	struct trace_config_data data;
+	data.want_cmd = cmd;
+	data.out = out;
+	repo_config(r, trace_config_cb, &data);
+}

trace.h

@@ -3,6 +3,9 @@
 
 #include "strbuf.h"
 
+struct repository;
+struct strvec;
+
 /**
  * The trace API can be used to print debug messages to stderr or a file. Trace
  * code is inactive unless explicitly enabled by setting `GIT_TRACE*` environment
@@ -127,6 +130,13 @@ void trace_command_performance(const char **argv);
 void trace_verbatim(struct trace_key *key, const void *buf, unsigned len);
 uint64_t trace_performance_enter(void);
 
+/**
+ * Load any trace-related config for git command "cmd", and insert the matching
+ * environment variables into "out", which is suitable for use by run-command
+ * and friends.
+ */
+void trace_config_for(struct repository *r, const char *cmd, struct strvec *out);
+
 /*
  * TRACE_CONTEXT may be set to __FUNCTION__ if the compiler supports it. The
  * default is __FILE__, as it is consistent with assert(), and static function