Shell: Cache PATH for faster tab completion

This patch reduces the O(n) tab completion to something like O(log(n)).
The cache is just a sorted vector of strings and we binary search it to
get a string matching our input, and then check the surrounding strings
to see if we need to remove any characters. Also we no longer stat each
file every time.

Also added an #include in BinarySearch since it was using size_t. Oops.

If `export` is called, we recache. Need to implement the `hash` builtin
for when an executable has been added to a directory in PATH.

AK/BinarySearch.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <AK/Types.h>
+
 namespace AK {
 
 template<typename T>

Shell/LineEditor.cpp

@@ -37,58 +37,70 @@ void LineEditor::append(const String& string)
     m_cursor = m_buffer.size();
 }
 
-void LineEditor::tab_complete_first_token()
+void LineEditor::cache_path()
 {
-    auto input = String::copy(m_buffer);
+    if (!m_path.is_empty())
+        m_path.clear_with_capacity();
 
     String path = getenv("PATH");
     if (path.is_empty())
         return;
+
     auto directories = path.split(':');
-
-    String match;
-
-    // Go through the files in PATH.
     for (const auto& directory : directories) {
         CDirIterator programs(directory.characters(), CDirIterator::SkipDots);
         while (programs.has_next()) {
-            String program = programs.next_path();
-            if (!program.starts_with(input))
-                continue;
+            auto program = programs.next_path();
 
-            // Check that the file is an executable program.
-            struct stat program_status;
             StringBuilder program_path;
             program_path.append(directory.characters());
             program_path.append('/');
             program_path.append(program.characters());
+            struct stat program_status;
             int stat_error = stat(program_path.to_string().characters(), &program_status);
             if (stat_error || !(program_status.st_mode & S_IXUSR))
                 continue;
 
-            // Set `match` to the first one that starts with `input`.
-            if (match.is_empty()) {
-                match = program;
-            } else {
-                // Remove characters from the end of `match` if they're
-                // different from another `program` starting with `input`.
-                int i = input.length();
-                while (i < match.length() && i < program.length() && match[i] == program[i])
-                    ++i;
-                match = match.substring(0, i);
-            }
-
-            if (match.length() == input.length())
-                return;
+            m_path.append(program.characters());
         }
     }
 
-    if (match.is_empty())
+    quick_sort(m_path.begin(), m_path.end(), AK::is_less_than<String>);
+}
+
+void LineEditor::cut_mismatching_chars(String& completion, const String& program, int token_length)
+{
+    int i = token_length;
+    while (i < completion.length() && i < program.length() && completion[i] == program[i])
+        ++i;
+    completion = completion.substring(0, i);
+}
+
+void LineEditor::tab_complete_first_token()
+{
+    String token = String::copy(m_buffer);
+
+    auto match = binary_search(m_path.data(), m_path.size(), token, [](const String& token, const String& program) -> int {
+        return strncmp(token.characters(), program.characters(), token.length());
+    });
+    if (!match)
         return;
 
-    // Then append `match` to the buffer, excluding the `input` part which is
-    // already in the buffer.
-    append(match.substring(input.length(), match.length() - input.length()).characters());
+    String completion = *match;
+
+    // Now that we have a program name starting with our token, we look at
+    // other program names starting with our token and cut off any mismatching
+    // characters.
+
+    int index = match - m_path.data();
+    for (int i = index - 1; i >= 0 && m_path[i].starts_with(token); --i)
+        cut_mismatching_chars(completion, m_path[i], token.length());
+    for (int i = index + 1; i < m_path.size() && m_path[i].starts_with(token); ++i)
+        cut_mismatching_chars(completion, m_path[i], token.length());
+
+    if (token.length() == completion.length())
+        return;
+    append(completion.substring(token.length(), completion.length() - token.length()).characters());
 }
 
 String LineEditor::get_line(const String& prompt)

Shell/LineEditor.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <AK/BinarySearch.h>
+#include <AK/QuickSort.h>
 #include <AK/String.h>
 #include <AK/StringBuilder.h>
 #include <AK/Vector.h>
@@ -16,9 +18,12 @@ public:
     void add_to_history(const String&);
     const Vector<String>& history() const { return m_history; }
 
+    void cache_path();
+
 private:
     void clear_line();
     void append(const String&);
+    void cut_mismatching_chars(String& completion, const String& program, int token_length);
     void tab_complete_first_token();
     void vt_save_cursor();
     void vt_restore_cursor();
@@ -32,6 +37,8 @@ private:
     int m_history_cursor { 0 };
     int m_history_capacity { 100 };
 
+    Vector<String, 256> m_path;
+
     enum class InputState {
         Free,
         ExpectBracket,

Shell/main.cpp

@@ -64,7 +64,12 @@ static int sh_export(int argc, char** argv)
         return 1;
     }
 
-    return setenv(parts[0].characters(), parts[1].characters(), 1);
+    int setenv_return = setenv(parts[0].characters(), parts[1].characters(), 1);
+
+    if (setenv_return == 0 && parts[0] == "PATH")
+        editor.cache_path();
+
+    return setenv_return;
 }
 
 static int sh_unset(int argc, char** argv)
@@ -910,6 +915,8 @@ int main(int argc, char** argv)
     load_history();
     atexit(save_history);
 
+    editor.cache_path();
+
     for (;;) {
         auto line = editor.get_line(prompt());
         if (line.is_empty())