ccmake: Use incremental rendering for the logs

This should avoid an exponential slowdown in the display time for
projects with lots of output.
This is still slower than cmake due to the ncurses drawing, but it should
now be O(L) in total and not O(L^2) wrt to output length.

Fixes: #20535

Source/CursesDialog/cmCursesLongMessageForm.cxx

@@ -35,6 +35,22 @@ cmCursesLongMessageForm::~cmCursesLongMessageForm()
   }
 }
 
+void cmCursesLongMessageForm::UpdateContent(std::string const& output,
+                                            std::string const& title)
+{
+  this->Title = title;
+
+  if (!output.empty() && this->Messages.size() < MAX_CONTENT_SIZE) {
+    this->Messages.append("\n" + output);
+    form_driver(this->Form, REQ_NEW_LINE);
+    this->DrawMessage(output.c_str());
+  }
+
+  this->UpdateStatusBar();
+  touchwin(stdscr);
+  refresh();
+}
+
 void cmCursesLongMessageForm::UpdateStatusBar()
 {
   int x;

Source/CursesDialog/cmCursesLongMessageForm.h

@@ -27,6 +27,8 @@ public:
   cmCursesLongMessageForm(cmCursesLongMessageForm const&) = delete;
   cmCursesLongMessageForm& operator=(cmCursesLongMessageForm const&) = delete;
 
+  void UpdateContent(std::string const& output, std::string const& title);
+
   // Description:
   // Handle user input.
   void HandleInput() override;

Source/CursesDialog/cmCursesMainForm.cxx

@@ -453,11 +453,11 @@ void cmCursesMainForm::UpdateProgress(const std::string& msg, float prog)
     this->LastProgress.append(progressBarCompleted, '#');
     this->LastProgress.append(progressBarWidth - progressBarCompleted, ' ');
     this->LastProgress += "] " + msg + "...";
+    this->DisplayOutputs(std::string());
   } else {
     this->Outputs.emplace_back(msg);
+    this->DisplayOutputs(msg);
   }
-
-  this->DisplayOutputs();
 }
 
 int cmCursesMainForm::Configure(int noconfigure)
@@ -589,7 +589,7 @@ void cmCursesMainForm::AddError(const std::string& message,
 {
   this->Outputs.emplace_back(message);
   this->HasNonStatusOutputs = true;
-  this->DisplayOutputs();
+  this->DisplayOutputs(message);
 }
 
 void cmCursesMainForm::RemoveEntry(const char* value)
@@ -995,18 +995,22 @@ void cmCursesMainForm::ResetOutputs()
   this->LastProgress.clear();
 }
 
-void cmCursesMainForm::DisplayOutputs()
+void cmCursesMainForm::DisplayOutputs(std::string const& newOutput)
 {
   int xi;
   int yi;
   getmaxyx(stdscr, yi, xi);
 
-  auto newLogForm = new cmCursesLongMessageForm(
-    this->Outputs, this->LastProgress.c_str(),
-    cmCursesLongMessageForm::ScrollBehavior::ScrollDown);
-  CurrentForm = newLogForm;
-  this->LogForm.reset(newLogForm);
-  this->LogForm->Render(1, 1, xi, yi);
+  if (CurrentForm != this->LogForm.get()) {
+    auto newLogForm = new cmCursesLongMessageForm(
+      this->Outputs, this->LastProgress.c_str(),
+      cmCursesLongMessageForm::ScrollBehavior::ScrollDown);
+    CurrentForm = newLogForm;
+    this->LogForm.reset(newLogForm);
+    this->LogForm->Render(1, 1, xi, yi);
+  } else {
+    this->LogForm->UpdateContent(newOutput, this->LastProgress);
+  }
 }
 
 const char* cmCursesMainForm::s_ConstHelpMessage =

Source/CursesDialog/cmCursesMainForm.h

@@ -129,7 +129,7 @@ protected:
   void ResetOutputs();
 
   // Display the current progress and output
-  void DisplayOutputs();
+  void DisplayOutputs(std::string const& newOutput);
 
   // Copies of cache entries stored in the user interface
   std::vector<cmCursesCacheEntryComposite> Entries;