Shell: Implement simple tab completion for commands and files

userspace/programs/Shell/main.cpp

@@ -1,9 +1,11 @@
 #include <BAN/HashMap.h>
 #include <BAN/Optional.h>
+#include <BAN/Sort.h>
 #include <BAN/String.h>
 #include <BAN/Vector.h>
 
 #include <ctype.h>
+#include <dirent.h>
 #include <limits.h>
 #include <pwd.h>
 #include <stdio.h>
@@ -834,6 +836,169 @@ static int source_shellrc()
 	return 0;
 }
 
+static BAN::Vector<BAN::String> list_matching_entries(BAN::StringView path, BAN::StringView start, bool require_executable)
+{
+	ASSERT(path.size() < PATH_MAX);
+
+	char path_cstr[PATH_MAX];
+	memcpy(path_cstr, path.data(), path.size());
+	path_cstr[path.size()] = '\0';
+
+	DIR* dirp = opendir(path_cstr);
+	if (dirp == nullptr)
+		return {};
+
+	BAN::Vector<BAN::String> result;
+
+	dirent* entry;
+	while ((entry = readdir(dirp)))
+	{
+		if (entry->d_name[0] == '.' && !start.starts_with("."_sv))
+			continue;
+		if (strncmp(entry->d_name, start.data(), start.size()))
+			continue;
+
+		struct stat st;
+		if (fstatat(dirfd(dirp), entry->d_name, &st, 0))
+			continue;
+
+		if (require_executable)
+		{
+			if (S_ISDIR(st.st_mode))
+				continue;
+			if (!(st.st_mode & (S_IXUSR | S_IXGRP | S_IXUSR)))
+				continue;
+		}
+
+		MUST(result.emplace_back(entry->d_name + start.size()));
+		if (S_ISDIR(st.st_mode))
+			MUST(result.back().push_back('/'));
+	}
+
+	closedir(dirp);
+
+	return BAN::move(result);
+}
+
+struct TabCompletion
+{
+	bool should_escape_spaces;
+	BAN::StringView prefix;
+	BAN::Vector<BAN::String> completions;
+};
+
+static TabCompletion list_tab_completion_entries(BAN::StringView command)
+{
+	enum class CompletionType
+	{
+		Command,
+		File,
+	};
+
+	BAN::StringView prefix = command;
+	BAN::String last_argument;
+	CompletionType completion_type = CompletionType::Command;
+
+	bool should_escape_spaces = true;
+	for (size_t i = 0; i < command.size(); i++)
+	{
+		if (command[i] == '\\')
+		{
+			i++;
+			if (i < command.size())
+				MUST(last_argument.push_back(command[i]));
+		}
+		else if (isspace(command[i]) || command[i] == ';' || command[i] == '|' || command.substring(i).starts_with("&&"_sv))
+		{
+			if (!isspace(command[i]))
+				completion_type = CompletionType::Command;
+			else if (!last_argument.empty())
+				completion_type = CompletionType::File;
+			if (auto rest = command.substring(i); rest.starts_with("||"_sv) || rest.starts_with("&&"_sv))
+				i++;
+			prefix = command.substring(i + 1);
+			last_argument.clear();
+			should_escape_spaces = true;
+		}
+		else if (command[i] == '\'' || command[i] == '"')
+		{
+			const char quote_type = command[i++];
+			while (i < command.size() && command[i] != quote_type)
+				MUST(last_argument.push_back(command[i++]));
+			should_escape_spaces = false;
+		}
+		else
+		{
+			MUST(last_argument.push_back(command[i]));
+		}
+	}
+
+	if (last_argument.sv().contains('/'))
+		completion_type = CompletionType::File;
+
+	BAN::Vector<BAN::String> result;
+	switch (completion_type)
+	{
+		case CompletionType::Command:
+		{
+			const char* path_env = getenv("PATH");
+			if (path_env)
+			{
+				auto splitted_path_env = MUST(BAN::StringView(path_env).split(':'));
+				for (auto path : splitted_path_env)
+				{
+					auto matching_entries = list_matching_entries(path, last_argument, true);
+					MUST(result.reserve(result.size() + matching_entries.size()));
+					for (auto&& entry : matching_entries)
+						MUST(result.push_back(BAN::move(entry)));
+				}
+			}
+
+			for (const auto& [builtin_name, _] : s_builtin_commands)
+			{
+				if (!builtin_name.sv().starts_with(last_argument))
+					continue;
+				MUST(result.emplace_back(builtin_name.sv().substring(last_argument.size())));
+			}
+
+			// TODO: match aliases when added
+
+			break;
+		}
+		case CompletionType::File:
+		{
+			BAN::String dir_path;
+			if (last_argument.sv().starts_with("/"_sv))
+				MUST(dir_path.push_back('/'));
+			else
+			{
+				char cwd_buffer[PATH_MAX];
+				if (getcwd(cwd_buffer, sizeof(cwd_buffer)) == nullptr)
+					return {};
+				MUST(dir_path.reserve(strlen(cwd_buffer) + 1));
+				MUST(dir_path.append(cwd_buffer));
+				MUST(dir_path.push_back('/'));
+			}
+
+			auto match_against = last_argument.sv();
+			if (auto idx = match_against.rfind('/'); idx.has_value())
+			{
+				MUST(dir_path.append(match_against.substring(0, idx.value())));
+				match_against = match_against.substring(idx.value() + 1);
+			}
+
+			result = list_matching_entries(dir_path, match_against, false);
+
+			break;
+		}
+	}
+
+	if (auto idx = prefix.rfind('/'); idx.has_value())
+		prefix = prefix.substring(idx.value() + 1);
+
+	return { should_escape_spaces, prefix, BAN::move(result) };
+}
+
 static int character_length(BAN::StringView prompt)
 {
 	int length { 0 };
@@ -1018,6 +1183,10 @@ int main(int argc, char** argv)
 	size_t index = 0;
 	size_t col = 0;
 
+	BAN::Optional<ssize_t> tab_index;
+	BAN::Optional<BAN::Vector<BAN::String>> tab_completions;
+	size_t tab_completion_keep = 0;
+
 	int waiting_utf8 = 0;
 
 	print_prompt();
@@ -1043,6 +1212,11 @@ int main(int argc, char** argv)
 		}
 
 		uint8_t ch = chi;
+		if (ch != '\t')
+		{
+			tab_completions.clear();
+			tab_index.clear();
+		}
 
 		if (waiting_utf8 > 0)
 		{
@@ -1168,8 +1342,114 @@ int main(int argc, char** argv)
 			col = 0;
 			break;
 		case '\t':
-			// FIXME: Implement tab completion or something
+		{
+			if (col != buffers[index].size())
+				continue;
+
+			if (tab_completions.has_value())
+			{
+				ASSERT(tab_completions->size() >= 2);
+
+				if (!tab_index.has_value())
+					tab_index = 0;
+				else
+				{
+					MUST(buffers[index].resize(tab_completion_keep));
+					col = tab_completion_keep;
+					*tab_index = (*tab_index + 1) % tab_completions->size();
+				}
+
+				MUST(buffers[index].append(tab_completions.value()[*tab_index]));
+				col += tab_completions.value()[*tab_index].size();
+
+				printf("\e[%dG%s\e[K", prompt_length() + 1, buffers[index].data());
+				fflush(stdout);
+
 				break;
+			}
+
+			tab_completion_keep = col;
+			auto [should_escape_spaces, prefix, completions] = list_tab_completion_entries(buffers[index].sv().substring(0, tab_completion_keep));
+
+			if (completions.empty())
+				break;
+
+			size_t all_match_len = 0;
+			for (;;)
+			{
+				if (completions.front().size() <= all_match_len)
+					break;
+				const char target = completions.front()[all_match_len];
+
+				bool all_matched = true;
+				for (const auto& completion : completions)
+				{
+					if (completion.size() > all_match_len && completion[all_match_len] == target)
+						continue;
+					all_matched = false;
+					break;
+				}
+
+				if (!all_matched)
+					break;
+				all_match_len++;
+			}
+
+			if (all_match_len)
+			{
+				col += all_match_len;
+				MUST(buffers[index].append(completions.front().sv().substring(0, all_match_len)));
+				printf("%.*s", (int)all_match_len, completions.front().data());
+				fflush(stdout);
+				break;
+			}
+
+			if (completions.size() == 1)
+			{
+				ASSERT(all_match_len == completions.front().size());
+				break;
+			}
+
+			BAN::sort::sort(completions.begin(), completions.end(),
+				[](const BAN::String& a, const BAN::String& b) {
+					if (auto cmp = strcmp(a.data(), b.data()))
+						return cmp < 0;
+					return a.size() < b.size();
+				}
+			);
+
+			printf("\n");
+			for (size_t i = 0; i < completions.size(); i++)
+			{
+				if (i != 0)
+					printf(" ");
+				const char* format = completions[i].sv().contains(' ') ? "'%.*s%s'" : "%.*s%s";
+				printf(format, (int)prefix.size(), prefix.data(), completions[i].data());
+			}
+			printf("\n");
+			print_prompt();
+			printf("%s", buffers[index].data());
+			fflush(stdout);
+
+			if (should_escape_spaces)
+			{
+				for (auto& completion : completions)
+				{
+					for (size_t i = 0; i < completion.size(); i++)
+					{
+						if (!isspace(completion[i]))
+							continue;
+						MUST(completion.insert('\\', i));
+						i++;
+					}
+				}
+			}
+
+			tab_completion_keep = col;
+			tab_completions = BAN::move(completions);
+
+			break;
+		}
 		default:
 			MUST(buffers[index].insert(ch, col++));
 			if (col == buffers[index].size())