Add prompt layout caching to layout_cache_t

src/fish_tests.cpp

@@ -4332,8 +4332,10 @@ void test_maybe() {
     do_test(m2.missing_or_empty());
 }
 
-void test_cached_esc_sequences() {
+void test_layout_cache() {
     layout_cache_t seqs;
+
+    // Verify escape code cache.
     do_test(seqs.find_escape_code(L"abc") == 0);
     seqs.add_escape_code(L"abc");
     seqs.add_escape_code(L"abc");
@@ -4354,6 +4356,24 @@ void test_cached_esc_sequences() {
     seqs.clear();
     do_test(seqs.esc_cache_size() == 0);
     do_test(seqs.find_escape_code(L"abcd") == 0);
+
+    // Verify prompt layout cache.
+    for (size_t i = 0; i < layout_cache_t::prompt_cache_max_size; i++) {
+        wcstring input = std::to_wstring(i);
+        do_test(!seqs.find_prompt_layout(input));
+        seqs.add_prompt_layout(input, {i});
+        do_test(seqs.find_prompt_layout(input)->line_count == i);
+    }
+
+    size_t expected_evictee = 3;
+    for (size_t i = 0; i < layout_cache_t::prompt_cache_max_size; i++) {
+        if (i != expected_evictee)
+            do_test(seqs.find_prompt_layout(std::to_wstring(i))->line_count == i);
+    }
+
+    seqs.add_prompt_layout(L"whatever", {100});
+    do_test(!seqs.find_prompt_layout(std::to_wstring(expected_evictee)));
+    do_test(seqs.find_prompt_layout(L"whatever")->line_count == 100);
 }
 
 /// Main test.
@@ -4452,7 +4472,7 @@ int main(int argc, char **argv) {
     if (should_test_function("string")) test_string();
     if (should_test_function("illegal_command_exit_code")) test_illegal_command_exit_code();
     if (should_test_function("maybe")) test_maybe();
-    if (should_test_function("cached_esc_sequences")) test_cached_esc_sequences();
+    if (should_test_function("layout_cache")) test_layout_cache();
     // history_tests_t::test_history_speed();
 
     say(L"Encountered %d errors in low-level tests", err_count);

src/screen.cpp

@@ -283,6 +283,27 @@ size_t escape_code_length(const wchar_t *code) {
     return esc_seq_len;
 }
 
+maybe_t<prompt_layout_t> layout_cache_t::find_prompt_layout(const wcstring &input) {
+    auto start = prompt_cache_.begin();
+    auto end = prompt_cache_.end();
+    for (auto iter = start; iter != end; ++iter) {
+        if (iter->first == input) {
+            // Found it. Move it to the front if not already there.
+            if (iter != start) prompt_cache_.splice(start, prompt_cache_, iter);
+            return iter->second;
+        }
+    }
+    return none();
+}
+
+void layout_cache_t::add_prompt_layout(wcstring input, prompt_layout_t layout) {
+    assert(!find_prompt_layout(input) && "Should not have a prompt layout for this input");
+    prompt_cache_.emplace_front(std::move(input), std::move(layout));
+    if (prompt_cache_.size() > prompt_cache_max_size) {
+        prompt_cache_.pop_back();
+    }
+}
+
 // These are used by `calc_prompt_layout()` to avoid redundant calculations.
 static const wchar_t *cached_left_prompt = wcsdup(L"");
 static const wchar_t *cached_right_prompt = wcsdup(L"");

src/screen.h

@@ -220,6 +220,8 @@ class layout_cache_t {
     std::list<prompt_layout_pair_t> prompt_cache_;
 
    public:
+    static constexpr size_t prompt_cache_max_size = 8;
+
     /// \return the size of the escape code cache.
     size_t esc_cache_size() const { return esc_cache_.size(); }
 
@@ -246,6 +248,12 @@ class layout_cache_t {
         return 0;
     }
 
+    // Finds the layout for a prompt, promoting it to the front. Returns none() if not found.
+    maybe_t<prompt_layout_t> find_prompt_layout(const wcstring &input);
+
+    // Adds a prompt layout for a given string.
+    void add_prompt_layout(wcstring input, prompt_layout_t layout);
+
     void clear() {
         esc_cache_.clear();
         prompt_cache_.clear();