refactor(signs): more efficient signcol calc

When iterating signs to calculate the sign column, stop iterating when
we reach the maximum configured from 'signcolumn'.

src/nvim/buffer.c

@@ -5455,30 +5455,43 @@ bool find_win_for_buf(buf_T *buf, win_T **wp, tabpage_T **tp)
   return false;
 }
 
-int buf_signcols(buf_T *buf)
+static int buf_signcols_inner(buf_T *buf, int maximum)
+{
+  sign_entry_T *sign;  // a sign in the sign list
+  int signcols = 0;
+  int linesum = 0;
+  linenr_T curline = 0;
+
+  FOR_ALL_SIGNS_IN_BUF(buf, sign) {
+    if (sign->se_lnum > curline) {
+      if (linesum > signcols) {
+        signcols = linesum;
+        if (signcols >= maximum) {
+          return maximum;
+        }
+      }
+      curline = sign->se_lnum;
+      linesum = 0;
+    }
+    if (sign->se_has_text_or_icon) {
+      linesum++;
+    }
+  }
+
+  if (linesum > signcols) {
+    signcols = linesum;
+    if (signcols >= maximum) {
+      return maximum;
+    }
+  }
+
+  return signcols;
+}
+
+int buf_signcols(buf_T *buf, int maximum)
 {
   if (!buf->b_signcols_valid) {
-    sign_entry_T *sign;  // a sign in the sign list
+    int signcols = buf_signcols_inner(buf, maximum);
-    int signcols = 0;
-    int linesum = 0;
-    linenr_T curline = 0;
-
-    FOR_ALL_SIGNS_IN_BUF(buf, sign) {
-      if (sign->se_lnum > curline) {
-        if (linesum > signcols) {
-          signcols = linesum;
-        }
-        curline = sign->se_lnum;
-        linesum = 0;
-      }
-      if (sign->se_has_text_or_icon) {
-        linesum++;
-      }
-    }
-    if (linesum > signcols) {
-      signcols = linesum;
-    }
-
     // Check if we need to redraw
     if (signcols != buf->b_signcols) {
       buf->b_signcols = signcols;

src/nvim/option.c

@@ -8046,7 +8046,6 @@ int win_signcol_count(win_T *wp)
 /// Return the number of requested sign columns, based on user / configuration.
 int win_signcol_configured(win_T *wp, int *is_fixed)
 {
-  int minimum = 0, maximum = 1, needed_signcols;
   const char *scl = (const char *)wp->w_p_scl;
 
   if (is_fixed) {
@@ -8059,7 +8058,6 @@ int win_signcol_configured(win_T *wp, int *is_fixed)
                                 && (wp->w_p_nu || wp->w_p_rnu)))) {
     return 0;
   }
-  needed_signcols = buf_signcols(wp->w_buffer);
 
   // yes or yes
   if (!strncmp(scl, "yes:", 4)) {
@@ -8075,6 +8073,8 @@ int win_signcol_configured(win_T *wp, int *is_fixed)
     *is_fixed = 0;
   }
 
+  int minimum = 0, maximum = 1;
+
   if (!strncmp(scl, "auto:", 5)) {
     // Variable depending on a configuration
     maximum = scl[5] - '0';
@@ -8085,7 +8085,8 @@ int win_signcol_configured(win_T *wp, int *is_fixed)
     }
   }
 
-  int ret = MAX(minimum, MIN(maximum, needed_signcols));
+  int needed_signcols = buf_signcols(wp->w_buffer, maximum);
+  int ret = MAX(minimum, needed_signcols);
   assert(ret <= SIGN_SHOW_MAX);
   return ret;
 }

src/nvim/screen.c

@@ -794,7 +794,7 @@ static void win_update(win_T *wp, Providers *providers)
   // If we can compute a change in the automatic sizing of the sign column
   // under 'signcolumn=auto:X' and signs currently placed in the buffer, better
   // figuring it out here so we can redraw the entire screen for it.
-  buf_signcols(buf);
+  win_signcol_count(wp);
 
   type = wp->w_redr_type;