diff --git a/src/array_view.hh b/src/array_view.hh
index 7ee32d12..34bc376e 100644
--- a/src/array_view.hh
+++ b/src/array_view.hh
@@ -1,7 +1,6 @@
 #ifndef array_view_hh_INCLUDED
 #define array_view_hh_INCLUDED
 
-#include <vector>
 #include <initializer_list>
 #include <iterator>
 
@@ -31,10 +30,10 @@ public:
     template<size_t N>
     constexpr ArrayView(T(&array)[N]) : m_pointer(array), m_size(N) {}
 
-    template<typename Alloc, typename U,
-             typename = std::enable_if_t<sizeof(U) == sizeof(T)>>
-    constexpr ArrayView(const std::vector<U, Alloc>& v)
-        : m_pointer(v.data()), m_size(v.size()) {}
+    template<typename Container,
+             typename = std::enable_if_t<sizeof(decltype(*std::declval<Container>().data())) == sizeof(T)>>
+    constexpr ArrayView(const Container& c)
+        : m_pointer(c.data()), m_size(c.size()) {}
 
     constexpr ArrayView(const std::initializer_list<T>& v)
         : m_pointer(v.begin()), m_size(v.size()) {}
diff --git a/src/commands.cc b/src/commands.cc
index a4c99f02..706e86b4 100644
--- a/src/commands.cc
+++ b/src/commands.cc
@@ -29,7 +29,6 @@
 #include "user_interface.hh"
 #include "window.hh"
 
-#include <cstring>
 #include <functional>
 #include <utility>
 
@@ -1851,7 +1850,7 @@ const CommandDesc prompt_cmd = {
         const String& command = parser[1];
         auto initstr = parser.get_switch("init").value_or(StringView{});
 
-        Completer completer;
+        PromptCompleter completer;
         if (parser.get_switch("file-completion"))
             completer = [](const Context& context, CompletionFlags,
                            StringView prefix, ByteCount cursor_pos) -> Completions {
@@ -1896,7 +1895,7 @@ const CommandDesc prompt_cmd = {
                 auto& text = sc.env_vars["text"_sv] = str.str();
                 auto clear_password = on_scope_end([&] {
                     if (flags & PromptFlags::Password)
-                        memset(text.data(), 0, (int)text.length());
+                        std::fill(text.begin(), text.end(), '\0');
                 });
 
                 ScopedSetBool disable_history{context.history_disabled()};
diff --git a/src/completion.hh b/src/completion.hh
index 553b37e7..1cfd1f22 100644
--- a/src/completion.hh
+++ b/src/completion.hh
@@ -42,9 +42,6 @@ enum class CompletionFlags
 
 constexpr bool with_bit_ops(Meta::Type<CompletionFlags>) { return true; }
 
-using Completer = std::function<Completions (const Context&, CompletionFlags,
-                                             StringView, ByteCount)>;
-
 inline Completions complete_nothing(const Context&, CompletionFlags,
                                     StringView, ByteCount cursor_pos)
 {
diff --git a/src/context.hh b/src/context.hh
index 14543946..d8830b2e 100644
--- a/src/context.hh
+++ b/src/context.hh
@@ -5,6 +5,8 @@
 #include "optional.hh"
 #include "utils.hh"
 
+#include <functional>
+
 namespace Kakoune
 {
 
diff --git a/src/hash.hh b/src/hash.hh
index e90232d8..23ae50a9 100644
--- a/src/hash.hh
+++ b/src/hash.hh
@@ -2,7 +2,7 @@
 #define hash_hh_INCLUDED
 
 #include <type_traits>
-#include <functional>
+#include <utility>
 
 #include <cstddef>
 
@@ -11,13 +11,6 @@ namespace Kakoune
 
 size_t hash_data(const char* data, size_t len);
 
-template<typename... Type>
-constexpr size_t hash_value(const Type&... val)
-{
-    static_assert(sizeof...(Type) == 1, "");
-    return std::hash<Type...>()(val...);
-}
-
 template<typename Type>
 std::enable_if_t<std::is_integral<Type>::value, size_t>
 constexpr hash_value(const Type& val)
diff --git a/src/highlighter.hh b/src/highlighter.hh
index cceabba2..dd5e2285 100644
--- a/src/highlighter.hh
+++ b/src/highlighter.hh
@@ -11,7 +11,7 @@
 #include "string.hh"
 #include "utils.hh"
 
-#include <functional>
+#include <memory>
 
 namespace Kakoune
 {
@@ -84,7 +84,7 @@ private:
 };
 
 using HighlighterParameters = ConstArrayView<String>;
-using HighlighterFactory = std::function<std::unique_ptr<Highlighter> (HighlighterParameters params, Highlighter* parent)>;
+using HighlighterFactory = std::unique_ptr<Highlighter> (*)(HighlighterParameters params, Highlighter* parent);
 
 struct HighlighterFactoryAndDocstring
 {
diff --git a/src/highlighters.cc b/src/highlighters.cc
index d39fbb69..05bc10e7 100644
--- a/src/highlighters.cc
+++ b/src/highlighters.cc
@@ -9,21 +9,16 @@
 #include "face_registry.hh"
 #include "highlighter_group.hh"
 #include "line_modification.hh"
-#include "option.hh"
 #include "option_types.hh"
 #include "parameters_parser.hh"
 #include "ranges.hh"
 #include "regex.hh"
 #include "register_manager.hh"
 #include "string.hh"
-#include "unit_tests.hh"
 #include "utf8.hh"
 #include "utf8_iterator.hh"
 #include "window.hh"
 
-#include <locale>
-#include <cstdio>
-
 namespace Kakoune
 {
 
diff --git a/src/hook_manager.hh b/src/hook_manager.hh
index bae6cca4..fa72cdc3 100644
--- a/src/hook_manager.hh
+++ b/src/hook_manager.hh
@@ -7,6 +7,8 @@
 #include "meta.hh"
 #include "enum.hh"
 
+#include <memory>
+
 namespace Kakoune
 {
 
diff --git a/src/input_handler.cc b/src/input_handler.cc
index 0d9710dd..91acbc3f 100644
--- a/src/input_handler.cc
+++ b/src/input_handler.cc
@@ -751,7 +751,7 @@ class Prompt : public InputMode
 public:
     Prompt(InputHandler& input_handler, StringView prompt,
            String initstr, String emptystr, Face face, PromptFlags flags,
-           Completer completer, PromptCallback callback)
+           PromptCompleter completer, PromptCallback callback)
         : InputMode(input_handler), m_prompt(prompt.str()), m_prompt_face(face),
           m_empty_text{std::move(emptystr)},
           m_flags(flags), m_completer(std::move(completer)), m_callback(std::move(callback)),
@@ -1064,8 +1064,8 @@ private:
             context().client().menu_hide();
     }
 
-    PromptCallback m_callback;
-    Completer      m_completer;
+    PromptCallback  m_callback;
+    PromptCompleter m_completer;
     const String   m_prompt;
     Face           m_prompt_face;
     Completions    m_completions;
@@ -1578,7 +1578,7 @@ void InputHandler::repeat_last_insert()
 
 void InputHandler::prompt(StringView prompt, String initstr, String emptystr,
                           Face prompt_face, PromptFlags flags,
-                          Completer completer, PromptCallback callback)
+                          PromptCompleter completer, PromptCallback callback)
 {
     push_mode(new InputModes::Prompt(*this, prompt, std::move(initstr), std::move(emptystr),
                                      prompt_face, flags, std::move(completer), std::move(callback)));
diff --git a/src/input_handler.hh b/src/input_handler.hh
index 600d78b8..35dc718a 100644
--- a/src/input_handler.hh
+++ b/src/input_handler.hh
@@ -47,6 +47,10 @@ enum class InsertMode : unsigned;
 enum class KeymapMode : char;
 enum class CursorMode;
 
+using PromptCompleter = std::function<Completions (const Context&, CompletionFlags,
+                                             StringView, ByteCount)>;
+
+
 class InputHandler : public SafeCountable
 {
 public:
@@ -66,7 +70,7 @@ public:
     // not change the mode itself
     void prompt(StringView prompt, String initstr, String emptystr,
                 Face prompt_face, PromptFlags flags,
-                Completer completer, PromptCallback callback);
+                PromptCompleter completer, PromptCallback callback);
     void set_prompt_face(Face prompt_face);
 
     // enter menu mode, callback is called on each selection change,
diff --git a/src/line_modification.cc b/src/line_modification.cc
index 30722368..d052cb54 100644
--- a/src/line_modification.cc
+++ b/src/line_modification.cc
@@ -90,8 +90,8 @@ Vector<LineModification> compute_line_modifications(const Buffer& buffer, size_t
 
 bool operator==(const LineModification& lhs, const LineModification& rhs)
 {
-    return std::tie(lhs.old_line, lhs.new_line, lhs.num_removed, lhs.num_added) ==
-           std::tie(rhs.old_line, rhs.new_line, rhs.num_removed, rhs.num_added);
+    return lhs.old_line == rhs.old_line and lhs.new_line == rhs.new_line and
+           lhs.num_removed == rhs.num_removed and lhs.num_added == rhs.num_added;
 }
 
 void LineRangeSet::update(ConstArrayView<LineModification> modifs)
diff --git a/src/line_modification.hh b/src/line_modification.hh
index cdc601df..5cb4d350 100644
--- a/src/line_modification.hh
+++ b/src/line_modification.hh
@@ -7,6 +7,8 @@
 #include "range.hh"
 #include "vector.hh"
 
+#include <functional>
+
 namespace Kakoune
 {
 
diff --git a/src/main.cc b/src/main.cc
index f0483835..b0b93edb 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -29,7 +29,6 @@
 #include "clock.hh"
 
 #include <fcntl.h>
-#include <locale>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
diff --git a/src/normal.hh b/src/normal.hh
index 9b6693cc..10ee5ffa 100644
--- a/src/normal.hh
+++ b/src/normal.hh
@@ -1,7 +1,6 @@
 #ifndef normal_hh_INCLUDED
 #define normal_hh_INCLUDED
 
-#include "context.hh"
 #include "optional.hh"
 #include "keys.hh"
 #include "keymap_manager.hh"
diff --git a/src/option_manager.hh b/src/option_manager.hh
index 77f482c0..81f3b1b9 100644
--- a/src/option_manager.hh
+++ b/src/option_manager.hh
@@ -11,7 +11,7 @@
 #include "string_utils.hh"
 
 #include <memory>
-#include <type_traits>
+#include <utility>
 
 namespace Kakoune
 {
diff --git a/src/safe_ptr.hh b/src/safe_ptr.hh
index 38d58046..216a14ff 100644
--- a/src/safe_ptr.hh
+++ b/src/safe_ptr.hh
@@ -6,9 +6,6 @@
 #include "assert.hh"
 #include "ref_ptr.hh"
 
-#include <type_traits>
-#include <utility>
-
 #ifdef SAFE_PTR_TRACK_CALLSTACKS
 #include "backtrace.hh"
 #include "vector.hh"
diff --git a/src/unicode.hh b/src/unicode.hh
index d94fff8d..486fc381 100644
--- a/src/unicode.hh
+++ b/src/unicode.hh
@@ -3,7 +3,6 @@
 
 #include <cwctype>
 #include <cwchar>
-#include <locale>
 
 #include "array_view.hh"
 #include "ranges.hh"
diff --git a/src/utf8_iterator.hh b/src/utf8_iterator.hh
index 4dd9ffd0..81302ef9 100644
--- a/src/utf8_iterator.hh
+++ b/src/utf8_iterator.hh
@@ -18,11 +18,15 @@ template<typename BaseIt,
          typename CodepointType = Codepoint,
          typename DifferenceType = CharCount,
          typename InvalidPolicy = utf8::InvalidPolicy::Pass>
-class iterator : public std::iterator<std::bidirectional_iterator_tag,
-                                      CodepointType, DifferenceType,
-                                      CodepointType*, CodepointType>
+class iterator
 {
 public:
+    using value_type = CodepointType;
+    using difference_type = DifferenceType;
+    using pointer = CodepointType*;
+    using reference = CodepointType&;
+    using iterator_category = std::bidirectional_iterator_tag;
+
     iterator() = default;
     constexpr static bool noexcept_policy = noexcept(InvalidPolicy{}(0));
 
diff --git a/src/window.cc b/src/window.cc
index a116abc4..b4bc922d 100644
--- a/src/window.cc
+++ b/src/window.cc
@@ -12,7 +12,6 @@
 #include "option_types.hh"
 
 #include <algorithm>
-#include <sstream>
 
 namespace Kakoune
 {
diff --git a/src/word_db.cc b/src/word_db.cc
index 6d847952..a9f0b751 100644
--- a/src/word_db.cc
+++ b/src/word_db.cc
@@ -1,10 +1,11 @@
 #include "word_db.hh"
 
-#include "utils.hh"
+#include "buffer.hh"
 #include "line_modification.hh"
 #include "option_types.hh"
-#include "utf8_iterator.hh"
 #include "unit_tests.hh"
+#include "utils.hh"
+#include "value.hh"
 
 namespace Kakoune
 {
@@ -20,7 +21,7 @@ WordDB& get_word_db(const Buffer& buffer)
 
 struct WordSplitter
 {
-    struct Iterator : std::iterator<std::forward_iterator_tag, StringView>
+    struct Iterator
     {
         Iterator(const char* begin, const WordSplitter& splitter)
             : m_word_begin{begin}, m_word_end{begin}, m_splitter{&splitter}
diff --git a/src/word_db.hh b/src/word_db.hh
index 08234257..aef047d0 100644
--- a/src/word_db.hh
+++ b/src/word_db.hh
@@ -1,16 +1,18 @@
 #ifndef word_db_hh_INCLUDED
 #define word_db_hh_INCLUDED
 
-#include "buffer.hh"
 #include "shared_string.hh"
 #include "hash_map.hh"
 #include "vector.hh"
 #include "ranked_match.hh"
+#include "option_manager.hh"
+#include "safe_ptr.hh"
 
 namespace Kakoune
 {
 
 using RankedMatchList = Vector<RankedMatch>;
+class Buffer;
 
 // maintain a database of words available in a buffer
 class WordDB : public OptionManagerWatcher