Expanded tab settings to accommodate different styles. (linux-test-project#455)

* Expanded tab settings to accommodate different styles.

'--num-spaces' now allows any numerical value.
alter apperance via negative values.
replace with spaces via positive values (backwards compatible).
do not alter tabs or their apperance via 0.
help and man pages updated to reflect the changes.
default (8) is unchanged.

minor tweak to man pages: num replaced with spaces for consistency.

NOTE: uses CSS3 'tab-size' (for altering tab apperance).
Widely available since 2021. Webkit since around 2013.

* fix typo

---------

Co-authored-by: Benedikt Roland <Benedikt.Roland@heidelberg-instruments.com>

Author: tDwtp

bin/genhtml

@@ -7254,12 +7254,6 @@ if ($css_filename) {
     }
 }
 
-# Make sure tab_size is within valid range
-if ($tab_size < 1) {
-    print(STDERR "ERROR: invalid number of spaces specified: $tab_size!\n");
-    exit(1);
-}
-
 # Get HTML prolog and epilog
 $html_prolog = get_html_prolog($html_prolog_file);
 $html_epilog = get_html_epilog($html_epilog_file);
@@ -7474,7 +7468,10 @@ HTML OUTPUT
       --header-title BANNER         Banner at top of each HTML page
       --footer FOOTER               Footer at bottom of each HTML page
       --no-sourceview               Do not create source code view
-      --num-spaces NUM              Replace tabs with NUM spaces in source view
+      --num-spaces NUM              change appearance of tabs in source view
+                                    NUM == 0 will not touch tabs
+                                    NUM > 0 will replace them with NUM spaces
+                                    NUM < 0 will only change their appearance
       --legend                      Include color legend in HTML output
       --html-prolog FILE            Use FILE as HTML prolog for generated pages
       --html-epilog FILE            Use FILE as HTML epilog for generated pages
@@ -8477,9 +8474,11 @@ sub escape_html($)
     $string =~ s/>/&gt;/g;       # > -> &gt;
     $string =~ s/\"/&quot;/g;    # " -> &quot;
 
-    while ($string =~ /^([^\t]*)(\t)/) {
-        my $replacement = " " x ($tab_size - (length($1) % $tab_size));
-        $string =~ s/^([^\t]*)(\t)/$1$replacement/;
+    if ($tab_size > 0) {
+        while ($string =~ /^([^\t]*)(\t)/) {
+            my $replacement = " " x ($tab_size - (length($1) % $tab_size));
+            $string =~ s/^([^\t]*)(\t)/$1$replacement/;
+        }
     }
 
     $string =~ s/\n/<br>/g;      # \n -> <br>
@@ -9358,6 +9357,7 @@ sub write_css_file()
           font-family: monospace;
           white-space: pre;
           margin-top: 2px;
+          tab-size: #TAB_SIZE;
         }
 
         /* elided/removed code */
@@ -9559,6 +9559,13 @@ END_OF_DATE_SPAN
         $css_data =~ s/$key/$color/gm;
     }
 
+    if ($tab_size < 0) {
+        my $abs_tab_size = abs($tab_size);
+        $css_data =~ s/#TAB_SIZE/$abs_tab_size/gm;
+    } else {
+        $css_data =~ s/^.*#TAB_SIZE.*\n//gm;
+    }
+
     print(CSS_HANDLE $css_data);
 
     close(CSS_HANDLE) or die("unable to close CSS handle: $!\n");

man/genhtml.1

@@ -2686,8 +2686,17 @@ the coverage criteria check or the serialized coverage DB,
 .RE
 .BI "\-\-num\-spaces " spaces
 .RS
-Replace tabs in source view with
-.I num
+Change appearance of tabs in source view according to
+.IR spaces .
+
+When set to 0, tabs and their behaviour will be the browser's default.
+.br
+Negative values will set the rendered width in the source view to
+.I spaces
+spaces.
+.br
+Positive values will replace tabs with
+.I spaces
 spaces.
 
 Default value is 8.