Fix Segfault and UX of the c3c project add-target subcommand (#1729)

* Fix UX of the `c3c project add-target` subcommand

- Fix segfault on `project.json` containing empty map `{}`
- Enable `add-target` to operate on non-existing project files
- Extend `add-target` syntax to accept source through CLI args

This enables the following workflow without friction and needless
crashes:

```console
$ cat > main.c3 <<END
import std::io;

fn void main() {
    io::printfn("Hello, World");
}
END
$ c3c project add-target main executable main.c3
$ c3c run
```

* Fix read_project() call in fetch_project()

* Keep the style of curlies consistent

Author: rexim

src/build/build.h

@@ -453,6 +453,7 @@ typedef struct BuildOptions_
 		ProjectSubcommand command;
 		const char *target_name;
 		TargetType target_type;
+		const char **sources;
 	} project_options;
 	CompileOption compile_option;
 	TrustLevel trust_level;

src/build/build_options.c

@@ -198,8 +198,8 @@ static void project_usage()
 	PRINTF("Usage: %s [<options>] project <subcommand> [<args>]", args[0]);
 	PRINTF("");
 	PRINTF("Project Subcommands:");
-	PRINTF("  view                                          view the current projects structure");
-	PRINTF("  add-target <name>  <target_type>              add a new target to the project");
+	PRINTF("  view                                            view the current projects structure");
+	PRINTF("  add-target <name>  <target_type>  [sources...]  add a new target to the project");
 	#if FETCH_AVAILABLE
 		PRINTF("  fetch              							fetch missing project libraries");
 	#endif
@@ -222,6 +222,11 @@ static void parse_project_subcommand(BuildOptions *options)
 		if (at_end() || next_is_opt()) error_exit("Expected a target type like 'executable' or 'static-lib'");
 		options->project_options.target_type = (TargetType)get_valid_enum_from_string(next_arg(), "type", targets, ELEMENTLEN(targets), "a target type like 'executable' or 'static-lib'");
 
+		while (!at_end() && !next_is_opt())
+		{
+			vec_add(options->project_options.sources, next_arg());
+		}
+
 		return;
 	}
 	if (arg_match("fetch"))

src/build/project_manipulation.c

@@ -3,12 +3,24 @@
 #define PRINTFN(string, ...) fprintf(stdout, string "\n", ##__VA_ARGS__) // NOLINT
 #define PRINTF(string, ...) fprintf(stdout, string, ##__VA_ARGS__) // NOLINT
 
-static JSONObject *read_project(const char **file_used)
+static JSONObject *read_project(const char **file_used, bool assume_empty_if_not_exists)
 {
 	size_t size;
 	const char *project_filename = file_exists(PROJECT_JSON5) ? PROJECT_JSON5 : PROJECT_JSON;
 	*file_used = project_filename;
-	char *read = file_read_all(project_filename, &size);
+	char *read;
+	if (assume_empty_if_not_exists)
+	{
+		// If project file does not exist assume the project simply being empty instead of
+		// failing. This is useful for such commands as `project add-target`. It enables
+		// them to update otherwise non-existing project files reducing the friction.
+		read = "{}";
+		if (file_exists(project_filename)) read = file_read_all(project_filename, &size);
+	}
+	else
+	{
+		read = file_read_all(project_filename, &size);
+	}
 	JsonParser parser;
 	json_init_string(&parser, read);
 	JSONObject *json = json_parse(&parser);
@@ -26,7 +38,7 @@ static JSONObject *read_project(const char **file_used)
 const char** get_project_dependency_directories()
 {
 	const char *filename;
-	JSONObject *json = read_project(&filename);
+	JSONObject *json = read_project(&filename, false);
 
 	const char *target = NULL;
 	const char **deps_dirs = NULL;
@@ -57,7 +69,7 @@ const char** get_project_dependencies()
 	const char *filename;
 	const char** dependencies = NULL;
 
-	JSONObject *project_json = read_project(&filename);
+	JSONObject *project_json = read_project(&filename, false);
 	JSONObject *dependencies_json = json_map_get(project_json, "dependencies");
 
 	FOREACH(JSONObject *, element, dependencies_json->elements)
@@ -290,7 +302,7 @@ void fetch_project(BuildOptions* options)
 	const char **libdirs = get_project_dependency_directories();
 	const char **deps = get_project_dependencies();
 	const char *filename;
-	JSONObject *project_json = read_project(&filename);
+	JSONObject *project_json = read_project(&filename, false);
 
 	JSONObject *targets_json = json_map_get(project_json, "targets");
 
@@ -359,7 +371,7 @@ void add_libraries_to_project_file(const char** libs, const char* target_name) {
 	//TODO! Target name option not implemented
 
 	const char *filename;
-	JSONObject *project_json = read_project(&filename);
+	JSONObject *project_json = read_project(&filename, false);
 
 	// TODO! check if target is specified and exists (NULL at the moment)
 	JSONObject *libraries_json = json_map_get(project_json, "dependencies");
@@ -396,9 +408,15 @@ void add_libraries_to_project_file(const char** libs, const char* target_name) {
 void add_target_project(BuildOptions *build_options)
 {
 	const char *filename;
-	JSONObject *project_json = read_project(&filename);
+	JSONObject *project_json = read_project(&filename, true);
 	JSONObject *targets_json = json_map_get(project_json, "targets");
 
+	if (targets_json == NULL)
+	{
+		targets_json = json_new_object(J_OBJECT);
+		json_map_set(project_json, "targets", targets_json);
+	}
+
 	if (json_map_get(targets_json, build_options->project_options.target_name) != NULL)
 	{
 		error_exit("Target with name '%s' already exists", build_options->project_options.target_name);
@@ -408,6 +426,12 @@ void add_target_project(BuildOptions *build_options)
 
 	JSONObject *new_target = json_new_map();
 	json_map_set(new_target, "type", target_type_obj);
+	JSONObject *target_sources = json_new_object(J_ARRAY);
+	FOREACH(const char *, source, build_options->project_options.sources)
+	{
+		vec_add(target_sources->elements, json_new_string(source));
+	}
+	json_map_set(new_target, "sources", target_sources);
 
 	json_map_set(targets_json, build_options->project_options.target_name, new_target);
 
@@ -419,7 +443,7 @@ void add_target_project(BuildOptions *build_options)
 void view_project(BuildOptions *build_options)
 {
 	const char *filename;
-	JSONObject *project_json = read_project(&filename);
+	JSONObject *project_json = read_project(&filename, false);
 
 	/* General information */
 	VIEW_MANDATORY_STRING_ARRAY("Authors", "authors");