Allow underscores in guifont PostScript names

runtime/doc/gui.txt

@@ -1135,10 +1135,18 @@ That's all.  XLFDs are not used.  For Chinese this is reported to work well: >
 
 MacVim							*macvim-guifont*
 
-For MacVim you can use something like this: >
-    :set guifont=Menlo:h10
-Fonts with spaces are set like this: >
+In MacVim, you can specify fonts by either the full PostScript name or the
+family name (both can be found in the Font Book app), followed by an optional
+font size (which defaults to `h11`).  Font names can also be completed in the
+cmdline using |complete-set-option|.
+
+Basic example of setting the font to Menlo with default size: >
+    :set guifont=Menlo
+To set a font by its family name which contains spaces: >
     :set guifont=DejaVu\ Sans\ Mono:h13
+When specifying family names with spaces, you can also use underscores
+instead: >
+    :set guifont=DejaVu_Sans_Mono:h13
 To use bold/italic fonts, use the fully specified PostScript name of the
 font, like so: >
     :set guifont=Menlo-Bold:h13

src/MacVim/gui_macvim.m

@@ -1196,12 +1196,6 @@
         parseFailed = YES;
     }
 
-    if (!parseFailed) {
-        // Replace underscores with spaces.
-        fontName = [[fontName componentsSeparatedByString:@"_"]
-                                 componentsJoinedByString:@" "];
-    }
-
     const BOOL isSystemFont = [fontName hasPrefix:MMSystemFontAlias];
     if (isSystemFont) {
         if (fontName.length > MMSystemFontAlias.length) {
@@ -1228,6 +1222,16 @@
                 || isSystemFont
                 || [NSFont fontWithName:fontName size:size])
             return [[NSString alloc] initWithFormat:@"%@:h%d", fontName, size];
+
+        // If font loading failed, try to replace underscores with spaces for
+        // user convenience. This really only works if the name is a family
+        // name because PostScript names should not have spaces.
+        if ([fontName rangeOfString:@"_"].location != NSNotFound) {
+            fontName = [fontName stringByReplacingOccurrencesOfString:@"_" withString:@" "];
+            if ([NSFont fontWithName:fontName size:size]) {
+                return [[NSString alloc] initWithFormat:@"%@:h%d", fontName, size];
+            }
+        }
     }
 
     return NOFONT;