Factor repainting decions from readline commands better in the reader

When typing into the command line, some actions should trigger repainting,
others should kick off syntax highlighting or autosuggestions, etc. Prior
to this change, these were all triggered in an ad-hoc manner. Each
possible

This change centralizes the logic around repainting. After each readline
command or text change, we compute the difference between what we would
draw and what was last drawn, and use that to decide whether to repaint
the screen.

This is a fairly involved change. Bugs here would show up as failing to
redraw, not reacting to a keypress, etc. However it better factors the
readline command handling from the drawing.

src/env_dispatch.cpp

@@ -197,7 +197,7 @@ void env_dispatch_var_change(const wcstring &key, env_stack_t &vars) {
 
     // Eww.
     if (string_prefixes_string(L"fish_color_", key)) {
-        reader_react_to_color_change();
+        reader_schedule_prompt_repaint();
     }
 }
 
@@ -220,7 +220,7 @@ void env_universal_callbacks(env_stack_t *stack, const callback_data_list_t &cal
 
 static void handle_fish_term_change(const env_stack_t &vars) {
     update_fish_color_support(vars);
-    reader_react_to_color_change();
+    reader_schedule_prompt_repaint();
 }
 
 static void handle_change_ambiguous_width(const env_stack_t &vars) {

src/flog.h

@@ -99,6 +99,7 @@ class category_list_t {
     category_t term_support{L"term-support", L"Terminal feature detection"};
 
     category_t reader{L"reader", L"The interactive reader/input system"};
+    category_t reader_render{L"reader-render", L"Rendering the command line"};
     category_t complete{L"complete", L"The completion system"};
     category_t path{L"path", L"Searching/using paths"};
 

src/input.cpp

@@ -271,7 +271,7 @@ static maybe_t<char_event_t> interrupt_handler() {
     event_fire_delayed(parser);
     // Reap stray processes, including printing exit status messages.
     // TODO: shouldn't need this parser here.
-    if (job_reap(parser, true)) reader_repaint_needed();
+    if (job_reap(parser, true)) reader_schedule_prompt_repaint();
     // Tell the reader an event occurred.
     if (reader_reading_interrupted()) {
         auto vintr = shell_modes.c_cc[VINTR];

src/pager.cpp

@@ -14,6 +14,7 @@
 #include "common.h"
 #include "complete.h"
 #include "fallback.h"
+#include "flog.h"
 #include "highlight.h"
 #include "pager.h"
 #include "reader.h"
@@ -575,26 +576,28 @@ page_rendering_t pager_t::render() const {
     return rendering;
 }
 
+bool pager_t::rendering_needs_update(const page_rendering_t &rendering) const {
+    // Common case is no pager.
+    if (this->empty() && rendering.screen_data.empty()) return false;
+
+    return rendering.term_width != this->available_term_width ||    //
+           rendering.term_height != this->available_term_height ||  //
+           rendering.selected_completion_idx !=
+               this->visual_selected_completion_index(rendering.rows, rendering.cols) ||    //
+           rendering.search_field_shown != this->search_field_shown ||                      //
+           rendering.search_field_line.text() != this->search_field_line.text() ||          //
+           rendering.search_field_line.position() != this->search_field_line.position() ||  //
+           (rendering.remaining_to_disclose > 0 && this->fully_disclosed);
+}
+
 void pager_t::update_rendering(page_rendering_t *rendering) const {
-    if (rendering->term_width != this->available_term_width ||
-        rendering->term_height != this->available_term_height ||
-        rendering->selected_completion_idx !=
-            this->visual_selected_completion_index(rendering->rows, rendering->cols) ||
-        rendering->search_field_shown != this->search_field_shown ||
-        rendering->search_field_line.text() != this->search_field_line.text() ||
-        rendering->search_field_line.position() != this->search_field_line.position() ||
-        (rendering->remaining_to_disclose > 0 && this->fully_disclosed)) {
+    if (rendering_needs_update(*rendering)) {
         *rendering = this->render();
     }
 }
 
-pager_t::pager_t()
-    : available_term_width(0),
-      available_term_height(0),
-      selected_completion_idx(PAGER_SELECTION_NONE),
-      suggested_row_start(0),
-      fully_disclosed(false),
-      search_field_shown(false) {}
+pager_t::pager_t() = default;
+pager_t::~pager_t() = default;
 
 bool pager_t::empty() const { return unfiltered_completion_infos.empty(); }
 
@@ -855,5 +858,4 @@ size_t pager_t::cursor_position() const {
     return result;
 }
 
-// Constructor
 page_rendering_t::page_rendering_t() = default;

src/pager.h

@@ -62,17 +62,17 @@ enum class selection_motion_t {
 #define PAGER_UNDISCLOSED_MAX_ROWS 4
 
 class pager_t {
-    size_t available_term_width;
-    size_t available_term_height;
+    size_t available_term_width{0};
+    size_t available_term_height{0};
 
-    size_t selected_completion_idx;
-    size_t suggested_row_start;
+    size_t selected_completion_idx{PAGER_SELECTION_NONE};
+    size_t suggested_row_start{0};
 
     // Fully disclosed means that we show all completions.
-    bool fully_disclosed;
+    bool fully_disclosed{false};
 
     // Whether we show the search field.
-    bool search_field_shown;
+    bool search_field_shown{false};
 
     // Returns the index of the completion that should draw selected, using the given number of
     // columns.
@@ -82,19 +82,15 @@ class pager_t {
     /// Data structure describing one or a group of related completions.
     struct comp_t {
         /// The list of all completion strings this entry applies to.
-        wcstring_list_t comp;
+        wcstring_list_t comp{};
         /// The description.
-        wcstring desc;
+        wcstring desc{};
         /// The representative completion.
-        completion_t representative;
+        completion_t representative{L""};
         /// On-screen width of the completion string.
-        size_t comp_width;
+        size_t comp_width{0};
         /// On-screen width of the description information.
-        size_t desc_width;
-        /// Minimum acceptable width.
-        // size_t min_width;
-
-        comp_t() : comp(), desc(), representative(L""), comp_width(0), desc_width(0) {}
+        size_t desc_width{0};
 
         // Our text looks like this:
         // completion  (description)
@@ -112,7 +108,7 @@ class pager_t {
     };
 
    private:
-    typedef std::vector<comp_t> comp_info_list_t;
+    using comp_info_list_t = std::vector<comp_t>;
 
     // The filtered list of completion infos.
     comp_info_list_t completion_infos;
@@ -165,7 +161,10 @@ class pager_t {
     // Produces a rendering of the completions, at the given term size.
     page_rendering_t render() const;
 
-    // Updates the rendering if it's stale.
+    // \return true if the given rendering needs to be updated.
+    bool rendering_needs_update(const page_rendering_t &rendering) const;
+
+    // Updates the rendering.
     void update_rendering(page_rendering_t *rendering) const;
 
     // Indicates if there are no completions, and therefore nothing to render.
@@ -192,8 +191,8 @@ class pager_t {
     // Position of the cursor.
     size_t cursor_position() const;
 
-    // Constructor
     pager_t();
+    ~pager_t();
 };
 
 #endif

src/reader.h

@@ -138,15 +138,9 @@ void reader_change_history(const wcstring &name);
 /// \param reset_cursor_position If set, issue a \r so the line driver knows where we are
 void reader_write_title(const wcstring &cmd, parser_t &parser, bool reset_cursor_position = true);
 
-/// Call this function to tell the reader that a repaint is needed, and should be performed when
-/// possible.
-void reader_repaint_needed();
-
-/// Call this function to tell the reader that some color has changed.
-void reader_react_to_color_change();
-
-/// Repaint immediately if needed.
-void reader_repaint_if_needed();
+/// Tell the reader that it needs to re-exec the prompt and repaint.
+/// This may be called in response to e.g. a color variable change.
+void reader_schedule_prompt_repaint();
 
 /// Enqueue an event to the back of the reader's input queue.
 class char_event_t;