process: provide cmdline-handling and execv style

Provide both cmdline-style handling (passing it to the shell on POSIX,
or directly to CreateProcess on win32) and execv style (passing it
directly to execv on POSIX, and mangling it into a single command-line
on win32).

src/util/process.h

@@ -43,7 +43,8 @@ typedef struct {
 
 /**
  * Create a new process.  The command to run should be specified as the
- * element of the `arg` array.
+ * element of the `arg` array, execv-style. This should be the full path
+ * to the command to run, the PATH is not obeyed.
  *
  * This function will add the given environment variables (in `env`)
  * to the current environment.  Operations on environment variables
@@ -67,8 +68,36 @@ extern int git_process_new(
 	size_t env_len,
 	git_process_options *opts);
 
+/**
+ * Create a new process. The command to run should be specified as the
+ * `cmdline` option - which is the full text of the command line as it
+ * would be specified or run by a user. The command to run will be
+ * looked up in the PATH.
+ *
+ * On Unix, this will be executed by the system's shell (`/bin/sh`)
+ * and may contain _Bourne-style_ shell quoting rules. On Windows,
+ * this will be passed to `CreateProcess`, and similarly, may
+ * contain _Windows-style_ shell quoting rules.
+ *
+ * This function will add the given environment variables (in `env`)
+ * to the current environment.  Operations on environment variables
+ * are not thread safe, so you may not modify the environment during
+ * this call.  You can avoid this by setting `exclude_env` in the
+ * options and providing the entire environment yourself.
+ */
+extern int git_process_new_from_cmdline(
+	git_process **out,
+	const char *cmdline,
+	const char **env,
+	size_t env_len,
+	git_process_options *opts);
+
 #ifdef GIT_WIN32
 
+extern int git_process__appname(
+	git_str *out,
+	const char *cmdline);
+
 /* Windows path parsing is tricky; this helper function is for testing. */
 extern int git_process__cmdline(
 	git_str *out,

src/util/unix/process.c

@@ -146,6 +146,19 @@ int git_process_new(
 	return 0;
 }
 
+extern int git_process_new_from_cmdline(
+	git_process **out,
+	const char *cmdline,
+	const char **env,
+	size_t env_len,
+	git_process_options *opts)
+{
+	const char *args[] = { "/bin/sh", "-c", cmdline };
+
+	return git_process_new(out,
+		args, ARRAY_SIZE(args), env, env_len, opts);
+}
+
 #define CLOSE_FD(fd) \
 	if (fd >= 0) {     \
 		close(fd); \

src/util/win32/process.c

@@ -162,30 +162,29 @@ done:
 	return ret < 0 ? -1 : 0;
 }
 
-int git_process_new(
+static int process_new(
 	git_process **out,
-	const char **args,
-	size_t args_len,
+	const char *appname,
+	const char *cmdline,
 	const char **env,
 	size_t env_len,
 	git_process_options *opts)
 {
 	git_process *process;
-	git_str cmdline = GIT_STR_INIT;
-	int error;
-
-	GIT_ASSERT_ARG(out && args && args_len > 0);
+	int error = 0;
 
 	*out = NULL;
 
 	process = git__calloc(1, sizeof(git_process));
 	GIT_ERROR_CHECK_ALLOC(process);
 
-	if ((error = git_process__cmdline(&cmdline, args, args_len)) < 0)
+	if (appname &&
+	    git_utf8_to_16_alloc(&process->appname, appname) < 0) {
+		error = -1;
 		goto done;
+	}
 
-	if (git_utf8_to_16_alloc(&process->appname, args[0]) < 0 ||
-	    git_utf8_to_16_alloc(&process->cmdline, cmdline.ptr) < 0) {
+	if (git_utf8_to_16_alloc(&process->cmdline, cmdline) < 0) {
 		error = -1;
 		goto done;
 	}
@@ -211,6 +210,40 @@ done:
 	else
 		*out = process;
 
+	return error;
+}
+
+int git_process_new_from_cmdline(
+	git_process **out,
+	const char *cmdline,
+	const char **env,
+	size_t env_len,
+	git_process_options *opts)
+{
+	GIT_ASSERT_ARG(out && cmdline);
+
+	return process_new(out, NULL, cmdline, env, env_len, opts);
+}
+
+int git_process_new(
+	git_process **out,
+	const char **args,
+	size_t args_len,
+	const char **env,
+	size_t env_len,
+	git_process_options *opts)
+{
+	git_str cmdline = GIT_STR_INIT;
+	int error;
+
+	GIT_ASSERT_ARG(out && args && args_len > 0);
+
+	if ((error = git_process__cmdline(&cmdline, args, args_len)) < 0)
+		goto done;
+
+	error = process_new(out, args[0], cmdline.ptr, env, env_len, opts);
+
+done:
 	git_str_dispose(&cmdline);
 	return error;
 }

tests/util/process/win32.c

@@ -10,8 +10,10 @@ static git_str result;
 		cl_assert_equal_s(expected, result.ptr); \
 		git_str_dispose(&result); \
 	} while(0)
+
 #endif
 
+
 void test_process_win32__cmdline_is_whitespace_delimited(void)
 {
 #ifdef GIT_WIN32