Bug 1410294 (part 3) - Overhaul static atom macros. r=froydnj.

There are four things that must be provided for every static atom, two of which have a macro: - the atom pointer declaration (no macro); - the atom pointer definition (no macro); - the atom char buffer (NS_STATIC_ATOM_BUFFER); - the StaticAtomSetup struct (NS_STATIC_ATOM_SETUP). This patch introduces new macros for the first two things: NS_STATIC_ATOM_DECL and NS_STATIC_ATOM_DEFN, and changes the arguments of the existing two macros to make them easier to use (e.g. all the '##' concatenation now happens within the macros). One consequence of the change is that all static atoms must be within a class, so the patch adds a couple of classes where necessary (DefaultAtoms, TSAtoms). The patch also adds a big comment explaining how the macros are used, and what their expansion looks like. This makes it a lot easier to understand how static atoms work. Correspondingly, the patch removes some small comments scattered around the macro use points. MozReview-Commit-ID: wpRyrEOTHE --HG-- extra : rebase_source : 9f85d477b4d06c9a9e710c757de1f1476edb6efe
2017-10-22 08:50:25 +11:00 · 2017-10-22 08:50:25 +11:00 · 21e7dce1a2
--- a/dom/base/nsGkAtoms.cpp
+++ b/dom/base/nsGkAtoms.cpp
@ -4,30 +4,23 @@
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

-/*
- * This class wraps up the creation (and destruction) of the standard
- * set of atoms used by gklayout; the atoms are created when gklayout
- * is loaded and they are destroyed when gklayout is unloaded.
- */
-
 #include "nsGkAtoms.h"
 #include "nsStaticAtom.h"

 using namespace mozilla;

-// define storage for all atoms
-#define GK_ATOM(name_, value_) nsAtom* nsGkAtoms::name_;
+#define GK_ATOM(name_, value_) NS_STATIC_ATOM_DEFN(nsGkAtoms, name_)
 #include "nsGkAtomList.h"
 #undef GK_ATOM

-#define GK_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_##_buffer, value_)
+#define GK_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_, value_)
 #include "nsGkAtomList.h"
 #undef GK_ATOM

 static const nsStaticAtomSetup sGkAtomSetup[] = {
-#define GK_ATOM(name_, value_) NS_STATIC_ATOM_SETUP(name_##_buffer, &nsGkAtoms::name_),
-#include "nsGkAtomList.h"
-#undef GK_ATOM
+  #define GK_ATOM(name_, value_) NS_STATIC_ATOM_SETUP(nsGkAtoms, name_)
+  #include "nsGkAtomList.h"
+  #undef GK_ATOM
 };

 void nsGkAtoms::AddRefAtoms()
--- a/dom/base/nsGkAtoms.h
+++ b/dom/base/nsGkAtoms.h
@ -4,32 +4,19 @@
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

-/*
- * This class wraps up the creation (and destruction) of the standard
- * set of atoms used by gklayout; the atoms are created when gklayout
- * is loaded and they are destroyed when gklayout is unloaded.
- */
-
 #ifndef nsGkAtoms_h___
 #define nsGkAtoms_h___

-class nsAtom;
+#include "nsStaticAtom.h"

-class nsGkAtoms {
+class nsGkAtoms
+{
 public:
-
  static void AddRefAtoms();

-  /* Declare all atoms
-
-     The atom names and values are stored in nsGkAtomList.h and
-     are brought to you by the magic of C preprocessing
-
-     Add new atoms to nsGkAtomList and all support logic will be auto-generated
-   */
-#define GK_ATOM(_name, _value) static nsAtom* _name;
-#include "nsGkAtomList.h"
-#undef GK_ATOM
+  #define GK_ATOM(_name, _value) NS_STATIC_ATOM_DECL(_name)
+  #include "nsGkAtomList.h"
+  #undef GK_ATOM
 };

 #endif /* nsGkAtoms_h___ */
--- a/editor/txtsvc/nsTextServicesDocument.cpp
+++ b/editor/txtsvc/nsTextServicesDocument.cpp
@ -76,10 +76,6 @@ public:
  bool    mIsValid;
 };

-#define TS_ATOM(name_, value_) nsAtom* nsTextServicesDocument::name_ = 0;
-#include "nsTSAtomList.h" // IWYU pragma: keep
-#undef TS_ATOM
-
 nsTextServicesDocument::nsTextServicesDocument()
 {
  mSelStartIndex  = -1;
@ -95,20 +91,31 @@ nsTextServicesDocument::~nsTextServicesDocument()
  ClearOffsetTable(&mOffsetTable);
 }

-#define TS_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_##_buffer, value_)
+class TSAtoms
+{
+public:
+  #define TS_ATOM(name_, value_) NS_STATIC_ATOM_DECL(name_)
+  #include "nsTSAtomList.h" // IWYU pragma: keep
+  #undef TS_ATOM
+};
+
+#define TS_ATOM(name_, value_) NS_STATIC_ATOM_DEFN(TSAtoms, name_)
 #include "nsTSAtomList.h" // IWYU pragma: keep
 #undef TS_ATOM

-/* static */
-void
+#define TS_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_, value_)
+#include "nsTSAtomList.h" // IWYU pragma: keep
+#undef TS_ATOM
+
+static const nsStaticAtomSetup sTSAtomSetup[] = {
+  #define TS_ATOM(name_, value_) NS_STATIC_ATOM_SETUP(TSAtoms, name_)
+  #include "nsTSAtomList.h" // IWYU pragma: keep
+  #undef TS_ATOM
+};
+
+/* static */ void
 nsTextServicesDocument::RegisterAtoms()
 {
-  static const nsStaticAtomSetup sTSAtomSetup[] = {
-#define TS_ATOM(name_, value_) NS_STATIC_ATOM_SETUP(name_##_buffer, &name_),
-#include "nsTSAtomList.h" // IWYU pragma: keep
-#undef TS_ATOM
-  };
-
  NS_RegisterStaticAtoms(sTSAtomSetup);
 }

@ -2040,32 +2047,32 @@ nsTextServicesDocument::IsBlockNode(nsIContent *aContent)

  nsAtom *atom = aContent->NodeInfo()->NameAtom();

-  return (sAAtom       != atom &&
-          sAddressAtom != atom &&
-          sBigAtom     != atom &&
-          sBAtom       != atom &&
-          sCiteAtom    != atom &&
-          sCodeAtom    != atom &&
-          sDfnAtom     != atom &&
-          sEmAtom      != atom &&
-          sFontAtom    != atom &&
-          sIAtom       != atom &&
-          sKbdAtom     != atom &&
-          sKeygenAtom  != atom &&
-          sNobrAtom    != atom &&
-          sSAtom       != atom &&
-          sSampAtom    != atom &&
-          sSmallAtom   != atom &&
-          sSpacerAtom  != atom &&
-          sSpanAtom    != atom &&
-          sStrikeAtom  != atom &&
-          sStrongAtom  != atom &&
-          sSubAtom     != atom &&
-          sSupAtom     != atom &&
-          sTtAtom      != atom &&
-          sUAtom       != atom &&
-          sVarAtom     != atom &&
-          sWbrAtom     != atom);
+  return (TSAtoms::sAAtom       != atom &&
+          TSAtoms::sAddressAtom != atom &&
+          TSAtoms::sBigAtom     != atom &&
+          TSAtoms::sBAtom       != atom &&
+          TSAtoms::sCiteAtom    != atom &&
+          TSAtoms::sCodeAtom    != atom &&
+          TSAtoms::sDfnAtom     != atom &&
+          TSAtoms::sEmAtom      != atom &&
+          TSAtoms::sFontAtom    != atom &&
+          TSAtoms::sIAtom       != atom &&
+          TSAtoms::sKbdAtom     != atom &&
+          TSAtoms::sKeygenAtom  != atom &&
+          TSAtoms::sNobrAtom    != atom &&
+          TSAtoms::sSAtom       != atom &&
+          TSAtoms::sSampAtom    != atom &&
+          TSAtoms::sSmallAtom   != atom &&
+          TSAtoms::sSpacerAtom  != atom &&
+          TSAtoms::sSpanAtom    != atom &&
+          TSAtoms::sStrikeAtom  != atom &&
+          TSAtoms::sStrongAtom  != atom &&
+          TSAtoms::sSubAtom     != atom &&
+          TSAtoms::sSupAtom     != atom &&
+          TSAtoms::sTtAtom      != atom &&
+          TSAtoms::sUAtom       != atom &&
+          TSAtoms::sVarAtom     != atom &&
+          TSAtoms::sWbrAtom     != atom);
 }

 bool
--- a/editor/txtsvc/nsTextServicesDocument.h
+++ b/editor/txtsvc/nsTextServicesDocument.h
@ -36,10 +36,6 @@ class nsTextServicesDocument final : public nsITextServicesDocument,
                                     public nsIEditActionListener
 {
 private:
-  #define TS_ATOM(name_, value_) static nsAtom* name_;
-  #include "nsTSAtomList.h" // IWYU pragma: keep
-  #undef TS_ATOM
-
  typedef enum { eIsDone=0,        // No iterator (I), or iterator doesn't point to anything valid.
                 eValid,           // I points to first text node (TN) in current block (CB).
                 ePrev,            // No TN in CB, I points to first TN in prev block.
--- a/layout/style/moz.build
+++ b/layout/style/moz.build
@ -218,7 +218,6 @@ UNIFIED_SOURCES += [
    'nsCSSParser.cpp',
    'nsCSSProps.cpp',
    'nsCSSPseudoClasses.cpp',
-    'nsCSSPseudoElements.cpp',
    'nsCSSRuleProcessor.cpp',
    'nsCSSRules.cpp',
    'nsCSSScanner.cpp',
@ -277,9 +276,12 @@ UNIFIED_SOURCES += [
    'URLExtraData.cpp',
 ]

-# - nsLayoutStylesheetCache.cpp needs to be built separately because it uses
-# nsExceptionHandler.h, which includes windows.h.
 SOURCES += [
+    # Both nsCSSPseudoElements.cpp and nsCSSPseudoClasses.cpp defined a
+    # 'mozPlaceholder' static atom.
+    'nsCSSPseudoElements.cpp',
+    # nsLayoutStylesheetCache.cpp uses nsExceptionHandler.h, which includes
+    # windows.h.
    'nsLayoutStylesheetCache.cpp',
 ]

--- a/layout/style/nsCSSAnonBoxes.cpp
+++ b/layout/style/nsCSSAnonBoxes.cpp
@ -13,32 +13,30 @@

 using namespace mozilla;

-// define storage for all atoms
 #define CSS_ANON_BOX(name_, value_) \
-  nsICSSAnonBoxPseudo* nsCSSAnonBoxes::name_;
+  NS_STATIC_ATOM_SUBCLASS_DEFN(nsICSSAnonBoxPseudo, nsCSSAnonBoxes, name_)
 #include "nsCSSAnonBoxList.h"
 #undef CSS_ANON_BOX

-#define CSS_ANON_BOX(name_, value_) \
-  NS_STATIC_ATOM_BUFFER(name_##_buffer, value_)
+#define CSS_ANON_BOX(name_, value_) NS_STATIC_ATOM_BUFFER(name_, value_)
 #include "nsCSSAnonBoxList.h"
 #undef CSS_ANON_BOX

 static const nsStaticAtomSetup sCSSAnonBoxAtomSetup[] = {
  // Put the non-inheriting anon boxes first, so we can index into them easily.
-#define CSS_ANON_BOX(name_, value_) /* nothing */
-#define CSS_NON_INHERITING_ANON_BOX(name_, value_) \
-  NS_STATIC_ATOM_SETUP(name_##_buffer, (nsAtom**)&nsCSSAnonBoxes::name_),
-#include "nsCSSAnonBoxList.h"
-#undef CSS_NON_INHERITING_ANON_BOX
-#undef CSS_ANON_BOX
+  #define CSS_ANON_BOX(name_, value_) /* nothing */
+  #define CSS_NON_INHERITING_ANON_BOX(name_, value_) \
+    NS_STATIC_ATOM_SUBCLASS_SETUP(nsCSSAnonBoxes, name_)
+  #include "nsCSSAnonBoxList.h"
+  #undef CSS_NON_INHERITING_ANON_BOX
+  #undef CSS_ANON_BOX

-#define CSS_ANON_BOX(name_, value_) \
-  NS_STATIC_ATOM_SETUP(name_##_buffer, (nsAtom**)&nsCSSAnonBoxes::name_),
-#define CSS_NON_INHERITING_ANON_BOX(name_, value_) /* nothing */
-#include "nsCSSAnonBoxList.h"
-#undef CSS_NON_INHERITING_ANON_BOX
-#undef CSS_ANON_BOX
+  #define CSS_ANON_BOX(name_, value_) \
+    NS_STATIC_ATOM_SUBCLASS_SETUP(nsCSSAnonBoxes, name_)
+  #define CSS_NON_INHERITING_ANON_BOX(name_, value_) /* nothing */
+  #include "nsCSSAnonBoxList.h"
+  #undef CSS_NON_INHERITING_ANON_BOX
+  #undef CSS_ANON_BOX
 };

 void nsCSSAnonBoxes::AddRefAtoms()
--- a/layout/style/nsCSSAnonBoxes.h
+++ b/layout/style/nsCSSAnonBoxes.h
@ -9,6 +9,7 @@
 #define nsCSSAnonBoxes_h___

 #include "nsAtom.h"
+#include "nsStaticAtom.h"

 // Empty class derived from nsAtom so that function signatures can
 // require an atom from this atom list.
@ -29,7 +30,8 @@ public:
           aPseudo == firstLetterContinuation;
  }

-#define CSS_ANON_BOX(_name, _value) static nsICSSAnonBoxPseudo* _name;
+#define CSS_ANON_BOX(name_, value_) \
+  NS_STATIC_ATOM_SUBCLASS_DECL(nsICSSAnonBoxPseudo, name_)
 #include "nsCSSAnonBoxList.h"
 #undef CSS_ANON_BOX

--- a/layout/style/nsCSSPseudoClasses.cpp
+++ b/layout/style/nsCSSPseudoClasses.cpp
@ -18,17 +18,6 @@

 using namespace mozilla;

-// define storage for all atoms
-#define CSS_PSEUDO_CLASS(_name, _value, _flags, _pref) \
-  static nsAtom* sPseudoClass_##_name;
-#include "nsCSSPseudoClassList.h"
-#undef CSS_PSEUDO_CLASS
-
-#define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
-  NS_STATIC_ATOM_BUFFER(name_##_pseudo_class_buffer, value_)
-#include "nsCSSPseudoClassList.h"
-#undef CSS_PSEUDO_CLASS
-
 #define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
  static_assert(!((flags_) & CSS_PSEUDO_CLASS_ENABLED_IN_CHROME) || \
                ((flags_) & CSS_PSEUDO_CLASS_ENABLED_IN_UA_SHEETS), \
@ -37,12 +26,30 @@ using namespace mozilla;
 #include "nsCSSPseudoClassList.h"
 #undef CSS_PSEUDO_CLASS

-// Array of nsStaticAtomSetup for each of the pseudo-classes.
-static const nsStaticAtomSetup sCSSPseudoClassAtomSetup[] = {
+class CSSPseudoClassAtoms
+{
+public:
+  #define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
+    NS_STATIC_ATOM_DECL(name_)
+  #include "nsCSSPseudoClassList.h"
+  #undef CSS_PSEUDO_CLASS
+};
+
 #define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
-  NS_STATIC_ATOM_SETUP(name_##_pseudo_class_buffer, &sPseudoClass_##name_),
+  NS_STATIC_ATOM_DEFN(CSSPseudoClassAtoms, name_)
 #include "nsCSSPseudoClassList.h"
 #undef CSS_PSEUDO_CLASS
+
+#define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
+  NS_STATIC_ATOM_BUFFER(name_, value_)
+#include "nsCSSPseudoClassList.h"
+#undef CSS_PSEUDO_CLASS
+
+static const nsStaticAtomSetup sCSSPseudoClassAtomSetup[] = {
+  #define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
+    NS_STATIC_ATOM_SETUP(CSSPseudoClassAtoms, name_)
+  #include "nsCSSPseudoClassList.h"
+  #undef CSS_PSEUDO_CLASS
 };

 // Flags data for each of the pseudo-classes, which must be separate
@ -50,39 +57,39 @@ static const nsStaticAtomSetup sCSSPseudoClassAtomSetup[] = {
 // nsStaticAtomSetup.
 /* static */ const uint32_t
 nsCSSPseudoClasses::kPseudoClassFlags[] = {
-#define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
-  flags_,
-#include "nsCSSPseudoClassList.h"
-#undef CSS_PSEUDO_CLASS
+  #define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
+    flags_,
+  #include "nsCSSPseudoClassList.h"
+  #undef CSS_PSEUDO_CLASS
 };

 /* static */ bool
 nsCSSPseudoClasses::sPseudoClassEnabled[] = {
-// If the pseudo class has any "ENABLED_IN" flag set, it is disabled by
-// default. Note that, if a pseudo class has pref, whatever its default
-// value is, it'll later be changed in nsCSSPseudoClasses::AddRefAtoms()
-// If the pseudo class has "ENABLED_IN" flags but doesn't have a pref,
-// it is an internal pseudo class which is disabled elsewhere.
-#define IS_ENABLED_BY_DEFAULT(flags_) \
-  (!((flags_) & CSS_PSEUDO_CLASS_ENABLED_MASK))
-#define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
-  IS_ENABLED_BY_DEFAULT(flags_),
-#include "nsCSSPseudoClassList.h"
-#undef CSS_PSEUDO_CLASS
-#undef IS_ENABLED_BY_DEFAULT
+  // If the pseudo class has any "ENABLED_IN" flag set, it is disabled by
+  // default. Note that, if a pseudo class has pref, whatever its default
+  // value is, it'll later be changed in nsCSSPseudoClasses::AddRefAtoms()
+  // If the pseudo class has "ENABLED_IN" flags but doesn't have a pref,
+  // it is an internal pseudo class which is disabled elsewhere.
+  #define IS_ENABLED_BY_DEFAULT(flags_) \
+    (!((flags_) & CSS_PSEUDO_CLASS_ENABLED_MASK))
+  #define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_) \
+    IS_ENABLED_BY_DEFAULT(flags_),
+  #include "nsCSSPseudoClassList.h"
+  #undef CSS_PSEUDO_CLASS
+  #undef IS_ENABLED_BY_DEFAULT
 };

 void nsCSSPseudoClasses::AddRefAtoms()
 {
  NS_RegisterStaticAtoms(sCSSPseudoClassAtomSetup);

-#define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_)                        \
-  if (pref_[0]) {                                                             \
-    auto idx = static_cast<CSSPseudoElementTypeBase>(Type::name_);            \
-    Preferences::AddBoolVarCache(&sPseudoClassEnabled[idx], pref_);           \
-  }
-#include "nsCSSPseudoClassList.h"
-#undef CSS_PSEUDO_CLASS
+  #define CSS_PSEUDO_CLASS(name_, value_, flags_, pref_)                      \
+    if (pref_[0]) {                                                           \
+      auto idx = static_cast<CSSPseudoElementTypeBase>(Type::name_);          \
+      Preferences::AddBoolVarCache(&sPseudoClassEnabled[idx], pref_);         \
+    }
+  #include "nsCSSPseudoClassList.h"
+  #undef CSS_PSEUDO_CLASS
 }

 bool
--- a/layout/style/nsCSSPseudoElements.cpp
+++ b/layout/style/nsCSSPseudoElements.cpp
@ -16,23 +16,22 @@

 using namespace mozilla;

-// define storage for all atoms
 #define CSS_PSEUDO_ELEMENT(name_, value_, flags_) \
-  nsICSSPseudoElement* nsCSSPseudoElements::name_;
+  NS_STATIC_ATOM_BUFFER(name_, value_)
 #include "nsCSSPseudoElementList.h"
 #undef CSS_PSEUDO_ELEMENT

 #define CSS_PSEUDO_ELEMENT(name_, value_, flags_) \
-  NS_STATIC_ATOM_BUFFER(name_##_pseudo_element_buffer, value_)
+  NS_STATIC_ATOM_SUBCLASS_DEFN(nsICSSPseudoElement, nsCSSPseudoElements, name_)
 #include "nsCSSPseudoElementList.h"
 #undef CSS_PSEUDO_ELEMENT

 // Array of nsStaticAtomSetup for each of the pseudo-elements.
 static const nsStaticAtomSetup sCSSPseudoElementAtomSetup[] = {
-#define CSS_PSEUDO_ELEMENT(name_, value_, flags_) \
-  NS_STATIC_ATOM_SETUP(name_##_pseudo_element_buffer, (nsAtom**)&nsCSSPseudoElements::name_),
-#include "nsCSSPseudoElementList.h"
-#undef CSS_PSEUDO_ELEMENT
+  #define CSS_PSEUDO_ELEMENT(name_, value_, flags_) \
+    NS_STATIC_ATOM_SUBCLASS_SETUP(nsCSSPseudoElements, name_)
+  #include "nsCSSPseudoElementList.h"
+  #undef CSS_PSEUDO_ELEMENT
 };

 // Flags data for each of the pseudo-elements, which must be separate
--- a/layout/style/nsCSSPseudoElements.h
+++ b/layout/style/nsCSSPseudoElements.h
@ -9,6 +9,7 @@
 #define nsCSSPseudoElements_h___

 #include "nsAtom.h"
+#include "nsStaticAtom.h"
 #include "mozilla/CSSEnabledState.h"
 #include "mozilla/Compiler.h"

@ -54,7 +55,7 @@ typedef uint8_t CSSPseudoElementTypeBase;
 enum class CSSPseudoElementType : CSSPseudoElementTypeBase {
  // If the actual pseudo-elements stop being first here, change
  // GetPseudoType.
-#define CSS_PSEUDO_ELEMENT(_name, _value_, _flags) \
+#define CSS_PSEUDO_ELEMENT(_name, _value, _flags) \
  _name,
 #include "nsCSSPseudoElementList.h"
 #undef CSS_PSEUDO_ELEMENT
@ -96,7 +97,7 @@ public:
  }

 #define CSS_PSEUDO_ELEMENT(_name, _value, _flags) \
-  static nsICSSPseudoElement* _name;
+  NS_STATIC_ATOM_SUBCLASS_DECL(nsICSSPseudoElement, _name)
 #include "nsCSSPseudoElementList.h"
 #undef CSS_PSEUDO_ELEMENT

--- a/parser/htmlparser/nsHTMLTags.cpp
+++ b/parser/htmlparser/nsHTMLTags.cpp
@ -23,14 +23,10 @@ const char16_t* const nsHTMLTags::sTagUnicodeTable[] = {
 #undef HTML_TAG
 #undef HTML_OTHER

-// static array of tag atoms
-nsAtom* nsHTMLTags::sTagAtomTable[eHTMLTag_userdefined - 1];
-
 int32_t nsHTMLTags::gTableRefCount;
 PLHashTable* nsHTMLTags::gTagTable;
 PLHashTable* nsHTMLTags::gTagAtomTable;

-
 // char16_t* -> id hash
 static PLHashNumber
 HTMLTagsHashCodeUCPtr(const void *key)
@ -56,29 +52,31 @@ HTMLTagsHashCodeAtom(const void *key)

 #define NS_HTMLTAG_NAME_MAX_LENGTH 10

-// static
-void
+// This would use NS_STATIC_ATOM_DEFN if it wasn't an array.
+nsAtom* nsHTMLTags::sTagAtomTable[eHTMLTag_userdefined - 1];
+
+#define HTML_TAG(_tag, _classname, _interfacename) \
+  NS_STATIC_ATOM_BUFFER(_tag, #_tag)
+#define HTML_OTHER(_tag)
+#include "nsHTMLTagList.h"
+#undef HTML_TAG
+#undef HTML_OTHER
+
+/* static */ void
 nsHTMLTags::RegisterAtoms(void)
 {
-#define HTML_TAG(_tag, _classname, _interfacename) NS_STATIC_ATOM_BUFFER(Atombuffer_##_tag, #_tag)
-#define HTML_OTHER(_tag)
-#include "nsHTMLTagList.h"
-#undef HTML_TAG
-#undef HTML_OTHER
-
-// static array of tag StaticAtom structs
-#define HTML_TAG(_tag, _classname, _interfacename) NS_STATIC_ATOM_SETUP(Atombuffer_##_tag, &nsHTMLTags::sTagAtomTable[eHTMLTag_##_tag - 1]),
-#define HTML_OTHER(_tag)
+  // This would use NS_STATIC_ATOM_SETUP if it wasn't an array.
  static const nsStaticAtomSetup sTagAtomSetup[] = {
-#include "nsHTMLTagList.h"
+    #define HTML_TAG(_tag, _classname, _interfacename) \
+      { _tag##_buffer, &nsHTMLTags::sTagAtomTable[eHTMLTag_##_tag - 1] },
+    #define HTML_OTHER(_tag)
+    #include "nsHTMLTagList.h"
+    #undef HTML_TAG
+    #undef HTML_OTHER
  };
-#undef HTML_TAG
-#undef HTML_OTHER

-  // Fill in our static atom pointers
  NS_RegisterStaticAtoms(sTagAtomSetup);

-
 #if defined(DEBUG)
  {
    // let's verify that all names in the the table are lowercase...
--- a/parser/htmlparser/nsHTMLTags.h
+++ b/parser/htmlparser/nsHTMLTags.h
@ -6,11 +6,10 @@
 #ifndef nsHTMLTags_h___
 #define nsHTMLTags_h___

+#include "nsStaticAtom.h"
 #include "nsString.h"
 #include "plhash.h"

-class nsAtom;
-
 /*
   Declare the enum list using the magic of preprocessing
   enum values are "eHTMLTag_foo" (where foo is the tag)
@ -76,6 +75,7 @@ public:
 #endif

 private:
+  // This would use NS_STATIC_ATOM_DECL if it wasn't an array.
  static nsAtom* sTagAtomTable[eHTMLTag_userdefined - 1];
  static const char16_t* const sTagUnicodeTable[];

--- a/rdf/base/nsRDFContentSink.cpp
+++ b/rdf/base/nsRDFContentSink.cpp
@ -126,9 +126,9 @@ public:
    static nsIRDFResource* kRDF_Seq;
    static nsIRDFResource* kRDF_nextVal;

-#define RDF_ATOM(name_, value_) static nsAtom* name_;
-#include "nsRDFContentSinkAtomList.h"
-#undef RDF_ATOM
+    #define RDF_ATOM(name_, value_) NS_STATIC_ATOM_DECL(name_)
+    #include "nsRDFContentSinkAtomList.h"
+    #undef RDF_ATOM

    typedef struct ContainerInfo {
        nsIRDFResource**  mType;
@ -235,18 +235,19 @@ mozilla::LazyLogModule RDFContentSinkImpl::gLog("nsRDFContentSink");

 ////////////////////////////////////////////////////////////////////////

-#define RDF_ATOM(name_, value_) nsAtom* RDFContentSinkImpl::name_;
+#define RDF_ATOM(name_, value_) NS_STATIC_ATOM_DEFN(RDFContentSinkImpl, name_)
 #include "nsRDFContentSinkAtomList.h"
 #undef RDF_ATOM

-#define RDF_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_##_buffer, value_)
+#define RDF_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_, value_)
 #include "nsRDFContentSinkAtomList.h"
 #undef RDF_ATOM

 static const nsStaticAtomSetup sRDFContentSinkAtomSetup[] = {
-#define RDF_ATOM(name_, value_) NS_STATIC_ATOM_SETUP(name_##_buffer, &RDFContentSinkImpl::name_),
-#include "nsRDFContentSinkAtomList.h"
-#undef RDF_ATOM
+  #define RDF_ATOM(name_, value_) \
+    NS_STATIC_ATOM_SETUP(RDFContentSinkImpl, name_)
+  #include "nsRDFContentSinkAtomList.h"
+  #undef RDF_ATOM
 };

 // static
--- a/xpcom/ds/nsAtomTable.cpp
+++ b/xpcom/ds/nsAtomTable.cpp
@ -13,6 +13,7 @@
 #include "mozilla/Sprintf.h"
 #include "mozilla/Unused.h"

+#include "nsAtom.h"
 #include "nsAtomTable.h"
 #include "nsStaticAtom.h"
 #include "nsString.h"
@ -482,6 +483,20 @@ static bool gStaticAtomTableSealed = false;
 // shrinking.
 #define ATOM_HASHTABLE_INITIAL_LENGTH  4096

+class DefaultAtoms
+{
+public:
+  NS_STATIC_ATOM_DECL(empty)
+};
+
+NS_STATIC_ATOM_DEFN(DefaultAtoms, empty)
+
+NS_STATIC_ATOM_BUFFER(empty, "")
+
+static const nsStaticAtomSetup sDefaultAtomSetup[] = {
+  NS_STATIC_ATOM_SETUP(DefaultAtoms, empty)
+};
+
 void
 NS_InitAtomTable()
 {
@ -496,11 +511,6 @@ NS_InitAtomTable()
  // static atom.  In order to avoid that, we register an empty string static
  // atom as soon as we initialize the atom table to guarantee that the empty
  // string atom will always be static.
-  NS_STATIC_ATOM_BUFFER(empty, "");
-  static nsAtom* empty_atom = nullptr;
-  static const nsStaticAtomSetup sDefaultAtomSetup[] = {
-    NS_STATIC_ATOM_SETUP(empty, &empty_atom)
-  };
  NS_RegisterStaticAtoms(sDefaultAtomSetup);
 }

--- a/xpcom/ds/nsStaticAtom.h
+++ b/xpcom/ds/nsStaticAtom.h
@ -7,31 +7,116 @@
 #ifndef nsStaticAtom_h__
 #define nsStaticAtom_h__

-#include "nsAtom.h"
-#include "nsStringBuffer.h"
+#include <stdint.h>

-#define NS_STATIC_ATOM_SETUP(buffer_name, atom_ptr) \
-  { buffer_name, atom_ptr }
+class nsAtom;

-// Note that |str_data| is an 8-bit string, and so |sizeof(str_data)| is equal
+// The following macros are used to define static atoms, typically in
+// conjunction with a .h file that defines the names and values of the atoms.
+//
+// For example, the .h file might be called MyAtomList.h and look like this:
+//
+//   MY_ATOM(one, "one")
+//   MY_ATOM(two, "two")
+//   MY_ATOM(three, "three")
+//
+// The code defining the static atoms might look like this:
+//
+//   class MyAtoms {
+//   public:
+//     #define MY_ATOM(_name, _value) NS_STATIC_ATOM_DECL(_name)
+//     #include "MyAtomList.h"
+//     #undef MY_ATOM
+//   };
+//
+//   #define MY_ATOM(name_, value_) NS_STATIC_ATOM_DEFN(MyAtoms, name_)
+//   #include "MyAtomList.h"
+//   #undef MY_ATOM
+//
+//   #define MY_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_, value_)
+//   #include "MyAtomList.h"
+//   #undef MY_ATOM
+//
+//   static const nsStaticAtomSetup sMyAtomSetup[] = {
+//     #define MY_ATOM(name_, value_) NS_STATIC_ATOM_SETUP(MyAtoms, name_)
+//     #include "MyAtomList.h"
+//     #undef MY_ATOM
+//   };
+//
+// The macros expand to the following:
+//
+//   class MyAtoms
+//   {
+//   public:
+//     static nsAtom* one;
+//     static nsAtom* two;
+//     static nsAtom* three;
+//   };
+//
+//   nsAtom* MyAtoms::one;
+//   nsAtom* MyAtoms::two;
+//   nsAtom* MyAtoms::three;
+//
+//   static const char16_t one_buffer[4] = u"one";     // plus a static_assert
+//   static const char16_t two_buffer[4] = u"two";     // plus a static_assert
+//   static const char16_t three_buffer[6] = u"three"; // plus a static_assert
+//
+//   static const nsStaticAtomSetup sMyAtomSetup[] = {
+//     { one_buffer, &MyAtoms::one },
+//     { two_buffer, &MyAtoms::two },
+//     { three_buffer, &MyAtoms::three },
+//   };
+//
+// When RegisterStaticAtoms(sMyAtomSetup) is called it iterates over
+// sMyAtomSetup[]. E.g. for the first atom it does roughly the following:
+// - MyAtoms::one = new nsAtom(one_buffer)
+// - inserts MyAtoms::one into the atom table
+
+// The declaration of the pointer to the static atom, which must be within a
+// class.
+#define NS_STATIC_ATOM_DECL(name_) \
+  static nsAtom* name_;
+
+// Like NS_STATIC_ATOM_DECL, but for sub-classes of nsAtom.
+#define NS_STATIC_ATOM_SUBCLASS_DECL(type_, name_) \
+  static type_* name_;
+
+// The definition of the pointer to the static atom. Initially null, it is
+// set by RegisterStaticAtoms() to point to a heap-allocated nsAtom.
+#define NS_STATIC_ATOM_DEFN(class_, name_) \
+  nsAtom* class_::name_;
+
+// Like NS_STATIC_ATOM_DEFN, but for sub-classes of nsAtom.
+#define NS_STATIC_ATOM_SUBCLASS_DEFN(type_, class_, name_) \
+  type_* class_::name_;
+
+// The buffer of 16-bit chars that constitute the static atom.
+//
+// Note that |value_| is an 8-bit string, and so |sizeof(value_)| is equal
 // to the number of chars (including the terminating '\0'). The |u""| prefix
-// converts |str_data| to a 16-bit string, which is assigned.
-#define NS_STATIC_ATOM_BUFFER(buffer_name, str_data) \
-  static const char16_t buffer_name[sizeof(str_data)] = u"" str_data; \
-  static_assert(sizeof(str_data[0]) == 1, "non-8-bit static atom literal");
+// converts |value_| to a 16-bit string, which is what is assigned.
+#define NS_STATIC_ATOM_BUFFER(name_, value_) \
+  static const char16_t name_##_buffer[sizeof(value_)] = u"" value_; \
+  static_assert(sizeof(value_[0]) == 1, "non-8-bit static atom literal");

-/**
- * Holds data used to initialize large number of atoms during startup. Use
- * the above macros to initialize these structs. They should never be accessed
- * directly other than from AtomTable.cpp.
- */
+// The StaticAtomSetup. Used only during start-up.
+#define NS_STATIC_ATOM_SETUP(class_, name_) \
+  { name_##_buffer, &class_::name_ },
+
+// Like NS_STATIC_ATOM_SUBCLASS, but for sub-classes of nsAtom.
+#define NS_STATIC_ATOM_SUBCLASS_SETUP(class_, name_) \
+  { name_##_buffer, reinterpret_cast<nsAtom**>(&class_::name_) },
+
+// Holds data used to initialize large number of atoms during startup. Use
+// NS_STATIC_ATOM_SETUP to initialize these structs. They should never be
+// accessed directly other than from nsAtomTable.cpp.
 struct nsStaticAtomSetup
 {
  const char16_t* const mString;
  nsAtom** const mAtom;
 };

-// Register an array of static atoms with the atom table
+// Register an array of static atoms with the atom table.
 template<uint32_t N>
 void
 NS_RegisterStaticAtoms(const nsStaticAtomSetup (&aSetup)[N])
--- a/xpcom/io/nsDirectoryService.cpp
+++ b/xpcom/io/nsDirectoryService.cpp
@ -105,18 +105,19 @@ nsDirectoryService::Create(nsISupports* aOuter, REFNSIID aIID, void** aResult)
  return gService->QueryInterface(aIID, aResult);
 }

-#define DIR_ATOM(name_, value_) nsAtom* nsDirectoryService::name_ = nullptr;
+#define DIR_ATOM(name_, value_) NS_STATIC_ATOM_DEFN(nsDirectoryService, name_)
 #include "nsDirectoryServiceAtomList.h"
 #undef DIR_ATOM

-#define DIR_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_##_buffer, value_)
+#define DIR_ATOM(name_, value_) NS_STATIC_ATOM_BUFFER(name_, value_)
 #include "nsDirectoryServiceAtomList.h"
 #undef DIR_ATOM

 static const nsStaticAtomSetup sDirectoryServiceAtomSetup[] = {
-#define DIR_ATOM(name_, value_) NS_STATIC_ATOM_SETUP(name_##_buffer, &nsDirectoryService::name_),
-#include "nsDirectoryServiceAtomList.h"
-#undef DIR_ATOM
+  #define DIR_ATOM(name_, value_) \
+    NS_STATIC_ATOM_SETUP(nsDirectoryService, name_)
+  #include "nsDirectoryServiceAtomList.h"
+  #undef DIR_ATOM
 };

 NS_IMETHODIMP
--- a/xpcom/io/nsDirectoryService.h
+++ b/xpcom/io/nsDirectoryService.h
@ -11,6 +11,7 @@
 #include "nsInterfaceHashtable.h"
 #include "nsIFile.h"
 #include "nsAtom.h"
+#include "nsStaticAtom.h"
 #include "nsTArray.h"
 #include "mozilla/Attributes.h"
 #include "mozilla/StaticPtr.h"
@ -54,13 +55,9 @@ private:
  nsTArray<nsCOMPtr<nsIDirectoryServiceProvider>> mProviders;

 public:
-
-#define DIR_ATOM(name_, value_) static nsAtom* name_;
-#include "nsDirectoryServiceAtomList.h"
-#undef DIR_ATOM
-
+  #define DIR_ATOM(name_, value_) NS_STATIC_ATOM_DECL(name_)
+  #include "nsDirectoryServiceAtomList.h"
+  #undef DIR_ATOM
 };

-
 #endif
-