ccmake: Improve coloring, allow customization

Change the default color for strings from BLUE (which is nearly
illegible on any terminals using the standard color palette which has
been around since at least CGA, almost 40 years ago) to CYAN. Add
ability to customize the colors via an environment variable (inspired by
LS_COLORS and using similar syntax).

Fixes: #20596

Source/CursesDialog/cmCursesColor.cxx

@@ -2,6 +2,12 @@
    file Copyright.txt or https://cmake.org/licensing for details.  */
 #include "cmCursesColor.h"
 
+#include <cctype>
+#include <cstdlib>
+#include <cstring>
+#include <unordered_map>
+#include <utility>
+
 #include "cmCursesStandardIncludes.h"
 
 bool cmCursesColor::HasColors()
@@ -19,11 +25,54 @@ void cmCursesColor::InitColors()
   if (HasColors()) {
     start_color();
     use_default_colors();
-    init_pair(cmCursesColor::BoolOff, COLOR_RED, -1);
-    init_pair(cmCursesColor::BoolOn, COLOR_GREEN, -1);
-    init_pair(cmCursesColor::String, COLOR_BLUE, -1);
-    init_pair(cmCursesColor::Path, COLOR_YELLOW, -1);
-    init_pair(cmCursesColor::Choice, COLOR_MAGENTA, -1);
+    init_pair(BoolOff, GetColor('N', COLOR_RED), -1);
+    init_pair(BoolOn, GetColor('Y', COLOR_GREEN), -1);
+    init_pair(String, GetColor('S', COLOR_CYAN), -1);
+    init_pair(Path, GetColor('P', COLOR_YELLOW), -1);
+    init_pair(Choice, GetColor('C', COLOR_MAGENTA), -1);
   }
 #endif
 }
+
+short cmCursesColor::GetColor(char id, short fallback)
+{
+  static bool initialized = false;
+  static std::unordered_map<char, short> env;
+
+  if (!initialized) {
+    if (auto* v = getenv("CCMAKE_COLORS")) {
+      while (v[0] && v[1] && v[1] == '=') {
+        auto const n = std::toupper(*v);
+
+        char buffer[12];
+        memset(buffer, 0, sizeof(buffer));
+
+        if (auto* const e = strchr(v, ':')) {
+          if (static_cast<size_t>(e - v) > sizeof(buffer)) {
+            break;
+          }
+
+          strncpy(buffer, v + 2, static_cast<size_t>(e - v - 2));
+          v = e + 1;
+        } else {
+          auto const l = strlen(v);
+          if (l > sizeof(buffer)) {
+            break;
+          }
+
+          strncpy(buffer, v + 2, l - 2);
+          v += l;
+        }
+
+        auto const c = atoi(buffer);
+        if (c && c < COLORS) {
+          env.emplace(n, static_cast<short>(c));
+        }
+      }
+    }
+    initialized = true;
+  }
+
+  auto const iter = env.find(id);
+  return (iter == env.end() ? fallback : iter->second);
+}

Source/CursesDialog/cmCursesColor.h

@@ -19,6 +19,9 @@ public:
   static bool HasColors();
 
   static void InitColors();
+
+protected:
+  static short GetColor(char id, short fallback);
 };
 
 #endif // cmCursesColor_h