Fix inheritance of relative font-sizes.

In particular, get the nexw 'late inheritance' test passing in inherit.t

Author: dwarring

Changes

@@ -1,4 +1,5 @@
 {{$NEXT}}
+    - Fix inheritance relative font-size calculations
 
 0.10.0  2025-04-29T08:40:14+12:00
     - Handle Pairs, List, Hash methods

lib/CSS/Properties.rakumod

@@ -178,7 +178,6 @@ Options:
 
     my @decls = self!build-declarations(@style);
     with $inherit -> CSS::Properties() $_ {
-        $!calc.em = .em;
         self.inherit: $_;
     }
 
@@ -613,6 +612,12 @@ multi sub to-ast($v, :$get = True) is default {
 
 #| CSS conformant inheritance from the given parent declaration list.
 method inherit(CSS::Properties:D() $css) {
+
+    $!calc.em = $css.measure: :font-size;
+    # font-size may be relative to parent, e.g. '.5em' or '85%'
+    $!calc.em = self.measure: :font-size($_)
+        with %!values<font-size>;
+
     for $css.properties -> \name {
         # skip unknown extension properties
         next if name.starts-with('-') && !self.prop-num(name).defined;
@@ -628,10 +633,7 @@ method inherit(CSS::Properties:D() $css) {
                 $inherit = True without %!values{name};
             }
             if $inherit {
-                my $val := $css.computed(name);
-                $!calc.em = $val
-                    if name eq 'font-size' && !%!values{name}.defined;
-                %!values{name} //= $val;
+                %!values{name} = $css.computed(name);
             }
         }
     }

lib/CSS/Properties/Calculator.rakumod

@@ -128,6 +128,7 @@ class CSS::Properties::Calculator {
         when Bool { CSS::Units.value($!em, $!units) }
         default   { %Compute<font-size>(self, $_) }
     }
+
     multi method measure(:$ref = 0, *%misc where .elems == 1) {
         my ($prop, $value) = %misc.kv;
         given $value {

t/css-fonts.t

@@ -1,6 +1,6 @@
 use v6;
 use Test;
-plan 3;
+plan 4;
 use CSS::Properties;
 
 my $style = 'font:italic bold 10pt/12pt times-roman;';
@@ -41,4 +41,10 @@ subtest 'issue#23', {
     is $css.clone.measure(:font-size), $css.measure(:font-size);
 }
 
+subtest 'change em', {
+    my CSS::Properties $css .= new: :style("font-size:.75em");
+    is $css.em, 9;
+    is $css.measure(:font-size), 9;
+}
+
 done-testing;

t/inherit.t

@@ -1,6 +1,6 @@
 use v6;
 use Test;
-plan 21;
+plan 23;
 use CSS::Properties;
 
 my $inherit = CSS::Properties.new: :style("margin-top:5pt; margin-right: 10pt; margin-left: 15pt; margin-bottom: 20pt; color:rgb(0,0,255)!important");
@@ -103,4 +103,22 @@ subtest 'issue#11 inheritence', {
     is $child, $style;
 }
 
+subtest 'early inheritence', {
+    my CSS::Properties() $inherit = 'font-size:20pt';
+    my CSS::Properties $css .= new: :style('border: .5em solid gray; font-size:.5em; margin:.5em'), :$inherit;
+    is $css.measure(:font-size), 10;
+    is $css.measure(:border-top-width), 5;
+    is $css.measure(:margin-top), 5;
+}
+
+subtest 'late inheritance', {
+    my CSS::Properties() $inherit = 'font-size:20pt';
+    my CSS::Properties $css .= new: :style('border: .5em solid gray; font-size:.5em; margin:.5em');
+    $css.inherit($inherit);
+    is $css.em, 10;
+    is $css.measure(:font-size), 10;
+    is $css.measure(:border-top-width), 5;
+    is $css.measure(:margin-top), 5;
+}
+
 done-testing;