Bug 1357432 (#750)

* Part 1. Move IsLocalRefURL to nsContentUtils to reuse this function. (port-rewrite)

`IsLocalRefURL` is originally designed to be used by URLValue only.
Since we need this function in SVGUseElement::LookupHref too, move it to nsContentUtils as a util function.

* Revert "Part 1. Move IsLocalRefURL to nsContentUtils to reuse this function. (port-rewrite)"

This reverts commit 19f010c62022e269f99066a8d90e3522fe31adaf.

* Part 1. Duplicate IsLocalRefURL to nsContentUtils to reuse this function.

`IsLocalRefURL` is originally designed to be used by URLValue only.
Since we need this function in SVGUseElement::LookupHref too, duplicate it to nsContentUtils as a util function.
This is a duplication because CSSValue uses stringbuffers and not nsStrings.
While Bug 1356060 - "Just use nsString in URLValueData" converts this use from stringbuffer to nsString, it builds on a bunch of vartype refactoring (nsString vs. nsAString, etc.) which is too much of a headache to deal with just to deduplicate this simple function.

* Part 2. Implement nsSVGEffects::GetBaseURLForLocalRef to export local-ref-url-resolving logic.

ResolveURLUsingLocalRef is designed to be internally used by nsSVGEffects::Get-{SVGEffect}-URI functions.
Since we also need it in SVGUseElement::LookupHref, make it public in nsSVGEffects.

* Part 3. Resolve local-ref in SVGUseElement::LookupHref by nsSVGEffects::GetBaseURLForLocalRef.

* Part 4. Reftest for using local-ref as xlink:href value.

3 files changed, 30 insertions, 2 deletions

diff --git a/dom/base/nsContentUtils.cpp b/dom/base/nsContentUtils.cpp
index 34c7d23b8..8612e76df 100644
--- a/dom/base/nsContentUtils.cpp
+++ b/dom/base/nsContentUtils.cpp
@@ -9787,3 +9787,19 @@ nsContentUtils::AttemptLargeAllocationLoad(nsIHttpChannel* aChannel)
 
   return reloadSucceeded;
 }
+
+/* static */ bool
+nsContentUtils::IsLocalRefURL(const nsString& aString)
+{
+  // Find the first non-"C0 controls + space" character.
+  const char16_t* current = aString.get();
+  for (; *current != '\0'; current++) {
+    if (*current > 0x20) {
+      // if the first non-"C0 controls + space" character is '#', this is a
+      // local-ref URL.
+      return *current == '#';
+    }
+  }
+
+  return false;
+}
\ No newline at end of file
diff --git a/dom/base/nsContentUtils.h b/dom/base/nsContentUtils.h
index 9ae6d2155..c255f813a 100644
--- a/dom/base/nsContentUtils.h
+++ b/dom/base/nsContentUtils.h
@@ -2730,6 +2730,13 @@ public:
 
   static bool AttemptLargeAllocationLoad(nsIHttpChannel* aChannel);
 
+  /**
+   * Detect whether a string is a (CSS) local-url.
+   * https://drafts.csswg.org/css-values/#local-urls
+   */
+  static bool
+  IsLocalRefURL(const nsString& aString);
+
 private:
   static bool InitializeEventTable();
 
diff --git a/dom/svg/SVGUseElement.cpp b/dom/svg/SVGUseElement.cpp
index 4911e2cac..9212ab1aa 100644
--- a/dom/svg/SVGUseElement.cpp
+++ b/dom/svg/SVGUseElement.cpp
@@ -15,6 +15,7 @@
 #include "mozilla/dom/Element.h"
 #include "nsContentUtils.h"
 #include "nsIURI.h"
+#include "nsSVGEffects.h"
 
 NS_IMPL_NS_NEW_NAMESPACED_SVG_ELEMENT(Use)
 
@@ -418,11 +419,15 @@ SVGUseElement::LookupHref()
     return;
   }
 
+  nsCOMPtr<nsIURI> originURI =
+    mOriginal ? mOriginal->GetBaseURI() : GetBaseURI();
+  nsCOMPtr<nsIURI> baseURI = nsContentUtils::IsLocalRefURL(href)
+    ? nsSVGEffects::GetBaseURLForLocalRef(this, originURI)
+    : originURI;
+
   nsCOMPtr<nsIURI> targetURI;
-  nsCOMPtr<nsIURI> baseURI = mOriginal ? mOriginal->GetBaseURI() : GetBaseURI();
   nsContentUtils::NewURIWithDocumentCharset(getter_AddRefs(targetURI), href,
                                             GetComposedDoc(), baseURI);
-
   mSource.Reset(this, targetURI);
 }