Auto merge of #14740 - glasserc:extremum-length, r=Manishearth

Add support for keyword values for min-width and max-width

This is a follow-up to #14432 which got closed and can no longer be re-opened.

This PR aims to add support for keyword-values max-content, min-content, fit-content, and fill-available to the properties that use them, namely min-width, min-height, max-width, and max-height.

It's still untested because I still haven't figured out how to do that. I guess I should write or find some web page that uses these properties.

Refs #13821.

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #13821  (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/style/properties/gecko.mako.rs

@@ -635,6 +635,8 @@ impl Debug for ${style_struct.gecko_struct_name} {
         "LengthOrPercentageOrAuto": impl_style_coord,
         "LengthOrPercentageOrNone": impl_style_coord,
         "LengthOrNone": impl_style_coord,
+        "MaxLength": impl_style_coord,
+        "MinLength": impl_style_coord,
         "Number": impl_simple,
         "Opacity": impl_simple,
         "CSSColor": impl_color,

components/style/properties/helpers/animated_properties.mako.rs

@@ -33,6 +33,7 @@ use values::Either;
 use values::computed::{Angle, LengthOrPercentageOrAuto, LengthOrPercentageOrNone};
 use values::computed::{BorderRadiusSize, ClipRect, LengthOrNone};
 use values::computed::{CalcLengthOrPercentage, Context, LengthOrPercentage};
+use values::computed::{MaxLength, MinLength};
 use values::computed::position::{HorizontalPosition, Position, VerticalPosition};
 use values::computed::ToComputedValue;
 use values::specified::Angle as SpecifiedAngle;
@@ -630,6 +631,34 @@ impl Interpolate for LengthOrPercentageOrNone {
     }
 }
 
+/// https://drafts.csswg.org/css-transitions/#animtype-lpcalc
+impl Interpolate for MinLength {
+    #[inline]
+    fn interpolate(&self, other: &Self, progress: f64) -> Result<Self, ()> {
+        match (*self, *other) {
+            (MinLength::LengthOrPercentage(ref this),
+             MinLength::LengthOrPercentage(ref other)) => {
+                this.interpolate(other, progress).map(MinLength::LengthOrPercentage)
+            }
+            _ => Err(()),
+        }
+    }
+}
+
+/// https://drafts.csswg.org/css-transitions/#animtype-lpcalc
+impl Interpolate for MaxLength {
+    #[inline]
+    fn interpolate(&self, other: &Self, progress: f64) -> Result<Self, ()> {
+        match (*self, *other) {
+            (MaxLength::LengthOrPercentage(ref this),
+             MaxLength::LengthOrPercentage(ref other)) => {
+                this.interpolate(other, progress).map(MaxLength::LengthOrPercentage)
+            }
+            _ => Err(()),
+        }
+    }
+}
+
 /// https://drafts.csswg.org/css-transitions/#animtype-number
 /// https://drafts.csswg.org/css-transitions/#animtype-length
 impl Interpolate for LineHeight {

components/style/properties/longhand/position.mako.rs

@@ -218,23 +218,40 @@ ${helpers.predefined_type("flex-basis",
                               spec=spec % size,
                               animatable=True, logical = logical)}
 
-    // min-width, min-height, min-block-size, min-inline-size
-    ${helpers.predefined_type("min-%s" % size,
-                              "LengthOrPercentage",
-                              "computed::LengthOrPercentage::Length(Au(0))",
-                              "parse_non_negative",
-                              needs_context=False,
-                              spec=spec % ("min-%s" % size),
-                              animatable=True, logical = logical)}
+    % if product == "gecko":
+        // min-width, min-height, min-block-size, min-inline-size
+        ${helpers.predefined_type("min-%s" % size,
+                                  "MinLength",
+                                  "computed::MinLength::LengthOrPercentage(" +
+                                  "computed::LengthOrPercentage::Length(Au(0)))",
+                                  spec=spec % ("min-%s" % size),
+                                  animatable=True, logical = logical)}
+    % else:
+        ${helpers.predefined_type("min-%s" % size,
+                                  "LengthOrPercentage",
+                                  "computed::LengthOrPercentage::Length(Au(0))",
+                                  "parse_non_negative",
+                                  needs_context=False,
+                                  spec=spec % ("min-%s" % size),
+                                  animatable=True, logical = logical)}
+    % endif
 
     // max-width, max-height, max-block-size, max-inline-size
-    ${helpers.predefined_type("max-%s" % size,
-                              "LengthOrPercentageOrNone",
-                              "computed::LengthOrPercentageOrNone::None",
-                              "parse_non_negative",
-                              needs_context=False,
-                              spec=spec % ("max-%s" % size),
-                              animatable=True, logical = logical)}
+    % if product == "gecko":
+        ${helpers.predefined_type("max-%s" % size,
+                                  "MaxLength",
+                                  "computed::MaxLength::None",
+                                  spec=spec % ("max-%s" % size),
+                                  animatable=True, logical = logical)}
+    % else:
+        ${helpers.predefined_type("max-%s" % size,
+                                  "LengthOrPercentageOrNone",
+                                  "computed::LengthOrPercentageOrNone::None",
+                                  "parse_non_negative",
+                                  needs_context=False,
+                                  spec=spec % ("max-%s" % size),
+                                  animatable=True, logical = logical)}
+    % endif
 % endfor
 
 ${helpers.single_keyword("box-sizing",