Auto merge of #13075 - emilio:calc-media, r=SimonSapin

style: Allow calc in media queries.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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- [x] There are tests for these changes OR

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Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=1290228

No tests have been added yet, I expect wpt to catch something, otherwise I'll write/import others.

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5 files changed, 72 insertions, 30 deletions

diff --git a/components/style/media_queries.rs b/components/style/media_queries.rs
index a5a4206a4a1..ed6dd2607bd 100644
--- a/components/style/media_queries.rs
+++ b/components/style/media_queries.rs
@@ -30,18 +30,23 @@ pub enum Range<T> {
 
 impl Range<specified::Length> {
     fn to_computed_range(&self, viewport_size: Size2D<Au>) -> Range<Au> {
+        // http://dev.w3.org/csswg/mediaqueries3/#units
+        // em units are relative to the initial font-size.
+        let initial_font_size = longhands::font_size::get_initial_value();
         let compute_width = |&width| {
             match width {
                 specified::Length::Absolute(value) => value,
-                specified::Length::FontRelative(value) => {
-                    // http://dev.w3.org/csswg/mediaqueries3/#units
-                    // em units are relative to the initial font-size.
-                    let initial_font_size = longhands::font_size::get_initial_value();
-                    value.to_computed_value(initial_font_size, initial_font_size)
-                }
-                specified::Length::ViewportPercentage(value) =>
-                    value.to_computed_value(viewport_size),
-                _ => unreachable!()
+                specified::Length::FontRelative(value)
+                    => value.to_computed_value(initial_font_size, initial_font_size),
+                specified::Length::ViewportPercentage(value)
+                    => value.to_computed_value(viewport_size),
+                specified::Length::Calc(val)
+                    => val.compute_from_viewport_and_font_size(viewport_size,
+                                                               initial_font_size,
+                                                               initial_font_size)
+                          .length(),
+                specified::Length::ServoCharacterWidth(..)
+                    => unreachable!(),
             }
         };
 
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 9864cd67983..265ed2f3a25 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -164,26 +164,9 @@ impl ToComputedValue for specified::CalcLengthOrPercentage {
     type ComputedValue = CalcLengthOrPercentage;
 
     fn to_computed_value(&self, context: &Context) -> CalcLengthOrPercentage {
-        let mut length = None;
-
-        if let Some(absolute) = self.absolute {
-            length = Some(length.unwrap_or(Au(0)) + absolute);
-        }
-
-        for val in &[self.vw, self.vh, self.vmin, self.vmax] {
-            if let Some(val) = *val {
-                length = Some(length.unwrap_or(Au(0)) +
-                    val.to_computed_value(context.viewport_size()));
-            }
-        }
-        for val in &[self.ch, self.em, self.ex, self.rem] {
-            if let Some(val) = *val {
-                length = Some(length.unwrap_or(Au(0)) + val.to_computed_value(
-                    context.style().get_font().clone_font_size(), context.style().root_font_size()));
-            }
-        }
-
-        CalcLengthOrPercentage { length: length, percentage: self.percentage.map(|p| p.0) }
+        self.compute_from_viewport_and_font_size(context.viewport_size(),
+                                                 context.style().get_font().clone_font_size(),
+                                                 context.style().root_font_size())
     }
 }
 
diff --git a/components/style/values/specified/mod.rs b/components/style/values/specified/mod.rs
index 77df3f94bdb..6746f6bb62c 100644
--- a/components/style/values/specified/mod.rs
+++ b/components/style/values/specified/mod.rs
@@ -16,7 +16,7 @@ use std::f32::consts::PI;
 use std::fmt;
 use std::ops::Mul;
 use style_traits::values::specified::AllowedNumericType;
-use super::computed::{Context, ToComputedValue};
+use super::computed::{self, Context, ToComputedValue};
 use super::{CSSFloat, FONT_MEDIUM_PX, HasViewportPercentage, LocalToCss, NoViewportPercentage};
 use url::Url;
 
@@ -751,6 +751,37 @@ impl CalcLengthOrPercentage {
             _ => Err(())
         }
     }
+
+    pub fn compute_from_viewport_and_font_size(&self,
+                                               viewport_size: Size2D<Au>,
+                                               font_size: Au,
+                                               root_font_size: Au)
+                                               -> computed::CalcLengthOrPercentage
+    {
+        let mut length = None;
+
+        if let Some(absolute) = self.absolute {
+            length = Some(length.unwrap_or(Au(0)) + absolute);
+        }
+
+        for val in &[self.vw, self.vh, self.vmin, self.vmax] {
+            if let Some(val) = *val {
+                length = Some(length.unwrap_or(Au(0)) +
+                    val.to_computed_value(viewport_size));
+            }
+        }
+        for val in &[self.ch, self.em, self.ex, self.rem] {
+            if let Some(val) = *val {
+                length = Some(length.unwrap_or(Au(0)) + val.to_computed_value(
+                    font_size, root_font_size));
+            }
+        }
+
+        computed::CalcLengthOrPercentage {
+            length: length,
+            percentage: self.percentage.map(|p| p.0)
+        }
+    }
 }
 
 impl HasViewportPercentage for CalcLengthOrPercentage {
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 6c127d66063..56c8b17b01f 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -6354,6 +6354,12 @@
             "url": "/_mozilla/css/float_relative_to_position.html"
           }
         ],
+        "css/media_calc_crash.html": [
+          {
+            "path": "css/media_calc_crash.html",
+            "url": "/_mozilla/css/media_calc_crash.html"
+          }
+        ],
         "css/meta_viewport_resize.html": [
           {
             "path": "css/meta_viewport_resize.html",
diff --git a/tests/wpt/mozilla/tests/css/media_calc_crash.html b/tests/wpt/mozilla/tests/css/media_calc_crash.html
new file mode 100644
index 00000000000..136a86cd4c2
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/media_calc_crash.html
@@ -0,0 +1,17 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>Don't crash when a media query with calc() is found.</title>
+<style>
+  @media (min-width: calc(60px)) {
+    pease-do {
+      not: crash;
+    }
+  }
+</style>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script>
+test(function() {
+  assert_true(true, "Reached here without crashing");
+})
+</script>