exernal/icu: Various C++20 comparison operator fixes

There are three patterns here:

* Missing const (source/common/uvector.cpp, source/common/uvector.h):  Overload
  resolution ambiguities when a synthesized canditate of operator == for a
  reversed-argument rewrite conflicts with the actual operator ==, due to the
  asymmetric const-ness of the implicit object parameter and the RHS parameter:

> uniset.cpp:360:18: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::UVector' and 'icu_63::UVector')
>     if (*strings != *o.strings) return FALSE;
>         ~~~~~~~~ ^  ~~~~~~~~~~
> ./uvector.h:385:23: note: candidate function
> inline UBool UVector::operator!=(const UVector& other) {
>                       ^
> ./uvector.h:116:11: note: candidate function
>     UBool operator==(const UVector& other);
>           ^
> ./uvector.h:116:11: note: candidate function (with reversed parameter order)

* UBool -> bool (source/i18n/tzrule.cpp, source/i18n/unicode/tzrule.h):
  [over.match.oper]/9 (of the current C++20 draft) states:  "If a rewritten
  operator== candidate is selected [...], its return type shall be cv bool":

> basictz.cpp:411:37: error: return type 'UBool' (aka 'signed char') of selected 'operator==' function for rewritten '==' comparison is not 'bool'
>                 if (*(tzt0.getTo()) == *tar) {
>                     ~~~~~~~~~~~~~~~ ^  ~~~~
> ./unicode/tzrule.h:675:19: note: declared here
>     virtual UBool operator==(const TimeZoneRule& that) const;
>                   ^

* Additional operator != (source/i18n/unicode/rbtz.h,
  source/i18n/unicode/simpletz.h, source/i18n/unicode/smpdtfmt.h,
  source/i18n/unicode/stsearch.h, source/i18n/unicode/tzrule.h,
  source/i18n/unicode/vtzone.h):  Similar to the previous pattern, but here the
  original operator used was !=, so an alternative fix (that reqires fewer
  changes to the code overall) is to add specific operator != overloads:

> rbtz.cpp:79:15: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::RuleBasedTimeZone' and 'const icu_63::RuleBasedTimeZone')
>     if (*this != right) {
>         ~~~~~ ^  ~~~~~
> ./unicode/rbtz.h:87:19: note: candidate function
>     virtual UBool operator!=(const TimeZone& that) const;
>                   ^
> ./unicode/rbtz.h:77:19: note: candidate function
>     virtual UBool operator==(const TimeZone& that) const;
>                   ^
> ./unicode/rbtz.h:77:19: note: candidate function (with reversed parameter order)
> rbtz.cpp:101:23: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::InitialTimeZoneRule' and 'icu_63::InitialTimeZoneRule')
>     if (*fInitialRule != *(rbtz->fInitialRule)) {
>         ~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~
> ./unicode/tzrule.h:257:19: note: candidate function
>     virtual UBool operator!=(const TimeZoneRule& that) const;
>                   ^
> ./unicode/tzrule.h:248:18: note: candidate function
>     virtual bool operator==(const TimeZoneRule& that) const;
>                  ^
> ./unicode/tzrule.h:248:18: note: candidate function (with reversed parameter order)
> rbtz.cpp:535:23: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::InitialTimeZoneRule' and 'icu_63::InitialTimeZoneRule')
>     if (*fInitialRule != *(that.fInitialRule)) {
>         ~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~
> ./unicode/tzrule.h:257:19: note: candidate function
>     virtual UBool operator!=(const TimeZoneRule& that) const;
>                   ^
> ./unicode/tzrule.h:248:18: note: candidate function
>     virtual bool operator==(const TimeZoneRule& that) const;
>                  ^
> ./unicode/tzrule.h:248:18: note: candidate function (with reversed parameter order)
>
> olsontz.cpp:630:69: error: return type 'UBool' (aka 'signed char') of selected 'operator==' function for rewritten '!=' comparison is not 'bool'
>         || (finalZone != NULL && z->finalZone != NULL && *finalZone != *z->finalZone)) {
>                                                          ~~~~~~~~~~ ^  ~~~~~~~~~~~~~
> ./unicode/simpletz.h:112:19: note: declared here
>     virtual UBool operator==(const TimeZone& that) const;
>                   ^

> dtitvfmt.cpp:223:62: error: return type 'UBool' (aka 'signed char') of selected 'operator==' function for rewritten '!=' comparison is not 'bool'
>         if (fDateFormat && fmt->fDateFormat && (*fDateFormat != *fmt->fDateFormat)) {return FALSE;}
>                                                 ~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~
> ./unicode/smpdtfmt.h:876:19: note: declared here
>     virtual UBool operator==(const Format& other) const;
>                   ^

> stsearch.cpp:187:17: error: return type 'UBool' (aka 'signed char') of selected 'operator==' function for rewritten '!=' comparison is not 'bool'
>     if ((*this) != that) {
>         ~~~~~~~ ^  ~~~~
> ./unicode/stsearch.h:299:19: note: declared here
>     virtual UBool operator==(const SearchIterator &that) const;
>                   ^

> vtzone.cpp:1003:15: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::VTimeZone' and 'const icu_63::VTimeZone')
>     if (*this != right) {
>         ~~~~~ ^  ~~~~~
> ./unicode/vtzone.h:83:19: note: candidate function
>     virtual UBool operator!=(const TimeZone& that) const;
>                   ^
> ./unicode/vtzone.h:73:19: note: candidate function
>     virtual UBool operator==(const TimeZone& that) const;
>                   ^
> ./unicode/vtzone.h:73:19: note: candidate function (with reversed parameter order)

Change-Id: I38e01143d1ea0df3f43de53303fd710e41bae027
Reviewed-on: https://gerrit.libreoffice.org/81306
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

2 files changed, 172 insertions, 0 deletions

diff --git a/external/icu/UnpackedTarball_icu.mk b/external/icu/UnpackedTarball_icu.mk
index d8a16e0e3777..4d45f2108f99 100644
--- a/external/icu/UnpackedTarball_icu.mk
+++ b/external/icu/UnpackedTarball_icu.mk
@@ -43,6 +43,7 @@ $(eval $(call gb_UnpackedTarball_add_patches,icu,\
 	external/icu/char8_t.patch \
 	external/icu/CVE-2018-18928.patch.2 \
 	external/icu/clang-cl.patch \
+	external/icu/c++20-comparison.patch \
 ))
 
 $(eval $(call gb_UnpackedTarball_add_file,icu,source/data/brkitr/khmerdict.dict,external/icu/khmerdict.dict))
diff --git a/external/icu/c++20-comparison.patch b/external/icu/c++20-comparison.patch
new file mode 100644
index 000000000000..44053e6719ca
--- /dev/null
+++ b/external/icu/c++20-comparison.patch
@@ -0,0 +1,171 @@
+--- source/common/uvector.cpp
++++ source/common/uvector.cpp
+@@ -110,7 +110,7 @@
+ }
+ 
+ // This only does something sensible if this object has a non-null comparer
+-UBool UVector::operator==(const UVector& other) {
++UBool UVector::operator==(const UVector& other) const {
+     int32_t i;
+     if (count != other.count) return FALSE;
+     if (comparer != NULL) {
+--- source/common/uvector.h
++++ source/common/uvector.h
+@@ -113,12 +113,12 @@
+      * equal if they are of the same size and all elements are equal,
+      * as compared using this object's comparer.
+      */
+-    UBool operator==(const UVector& other);
++    UBool operator==(const UVector& other) const;
+ 
+     /**
+      * Equivalent to !operator==()
+      */
+-    inline UBool operator!=(const UVector& other);
++    inline UBool operator!=(const UVector& other) const;
+ 
+     //------------------------------------------------------------
+     // java.util.Vector API
+@@ -382,7 +382,7 @@
+     return elementAt(index);
+ }
+ 
+-inline UBool UVector::operator!=(const UVector& other) {
++inline UBool UVector::operator!=(const UVector& other) const {
+     return !operator==(other);
+ }
+ 
+--- source/i18n/tzrule.cpp
++++ source/i18n/tzrule.cpp
+@@ -53,7 +53,7 @@
+     return *this;
+ }
+ 
+-UBool
++bool
+ TimeZoneRule::operator==(const TimeZoneRule& that) const {
+     return ((this == &that) ||
+             (typeid(*this) == typeid(that) &&
+@@ -120,7 +120,7 @@
+     return *this;
+ }
+ 
+-UBool
++bool
+ InitialTimeZoneRule::operator==(const TimeZoneRule& that) const {
+     return ((this == &that) ||
+             (typeid(*this) == typeid(that) &&
+@@ -226,7 +226,7 @@
+     return *this;
+ }
+ 
+-UBool
++bool
+ AnnualTimeZoneRule::operator==(const TimeZoneRule& that) const {
+     if (this == &that) {
+         return TRUE;
+@@ -445,7 +445,7 @@
+     return *this;
+ }
+ 
+-UBool
++bool
+ TimeArrayTimeZoneRule::operator==(const TimeZoneRule& that) const {
+     if (this == &that) {
+         return TRUE;
+--- source/i18n/unicode/rbtz.h
++++ source/i18n/unicode/rbtz.h
+@@ -85,6 +85,7 @@
+      * @stable ICU 3.8
+      */
+     virtual UBool operator!=(const TimeZone& that) const;
++    UBool operator!=(const RuleBasedTimeZone& that) const {return !operator==(that);}
+ 
+     /**
+      * Adds the <code>TimeZoneRule</code> which represents time transitions.
+--- source/i18n/unicode/simpletz.h
++++ source/i18n/unicode/simpletz.h
+@@ -110,6 +110,7 @@
+      * @stable ICU 2.0
+      */
+     virtual UBool operator==(const TimeZone& that) const;
++    UBool operator!=(const SimpleTimeZone& that) const {return !operator==(that);}
+ 
+     /**
+      * Constructs a SimpleTimeZone with the given raw GMT offset and time zone ID,
+--- source/i18n/unicode/smpdtfmt.h
++++ source/i18n/unicode/smpdtfmt.h
+@@ -874,6 +874,7 @@
+      * @stable ICU 2.0
+      */
+     virtual UBool operator==(const Format& other) const;
++    UBool operator!=(const SimpleDateFormat& that) const {return !operator==(that);}
+ 
+ 
+     using DateFormat::format;
+--- source/i18n/unicode/stsearch.h
++++ source/i18n/unicode/stsearch.h
+@@ -297,6 +297,7 @@
+      * @stable ICU 2.0
+      */
+     virtual UBool operator==(const SearchIterator &that) const;
++    UBool operator!=(const StringSearch &that) const {return !operator==(that);}
+ 
+     // public get and set methods ----------------------------------------
+ 
+--- source/i18n/unicode/tzrule.h
++++ source/i18n/unicode/tzrule.h
+@@ -54,7 +54,7 @@
+      * @return  true if the given <code>TimeZoneRule</code> objects are semantically equal.
+      * @stable ICU 3.8
+      */
+-    virtual UBool operator==(const TimeZoneRule& that) const;
++    virtual bool operator==(const TimeZoneRule& that) const;
+ 
+     /**
+      * Return true if the given <code>TimeZoneRule</code> objects are semantically unequal. Objects
+@@ -245,7 +245,7 @@
+      * @return  true if the given <code>TimeZoneRule</code> objects are semantically equal.
+      * @stable ICU 3.8
+      */
+-    virtual UBool operator==(const TimeZoneRule& that) const;
++    virtual bool operator==(const TimeZoneRule& that) const;
+ 
+     /**
+      * Return true if the given <code>TimeZoneRule</code> objects are semantically unequal. Objects
+@@ -255,6 +255,7 @@
+      * @stable ICU 3.8
+      */
+     virtual UBool operator!=(const TimeZoneRule& that) const;
++    UBool operator!=(const InitialTimeZoneRule& that) const {return !operator==(that);}
+ 
+     /**
+      * Gets the time when this rule takes effect in the given year.
+@@ -456,7 +457,7 @@
+      * @return  true if the given <code>TimeZoneRule</code> objects are semantically equal.
+      * @stable ICU 3.8
+      */
+-    virtual UBool operator==(const TimeZoneRule& that) const;
++    virtual bool operator==(const TimeZoneRule& that) const;
+ 
+     /**
+      * Return true if the given <code>TimeZoneRule</code> objects are semantically unequal. Objects
+@@ -672,7 +673,7 @@
+      * @return  true if the given <code>TimeZoneRule</code> objects are semantically equal.
+      * @stable ICU 3.8
+      */
+-    virtual UBool operator==(const TimeZoneRule& that) const;
++    virtual bool operator==(const TimeZoneRule& that) const;
+ 
+     /**
+      * Return true if the given <code>TimeZoneRule</code> objects are semantically unequal. Objects
+--- source/i18n/unicode/vtzone.h
++++ source/i18n/unicode/vtzone.h
+@@ -81,6 +81,7 @@
+      * @stable ICU 3.8
+      */
+     virtual UBool operator!=(const TimeZone& that) const;
++    UBool operator!=(const VTimeZone& that) const {return !operator==(that);}
+ 
+     /**
+      * Create a <code>VTimeZone</code> instance by the time zone ID.