[default] Build a no-op number formatter for old ICUs

This has been causing too many build problems and it is
a major source of complains because of different ICU interfaces.

platform/default/src/mbgl/i18n/number_format.cpp

@@ -1,10 +1,16 @@
 #include <mbgl/i18n/number_format.hpp>
 
+#if !defined(MBGL_USE_BUILTIN_ICU)
 #include <unicode/numberformatter.h>
+#include <unicode/uvernum.h>
+#endif
+
+#include <string>
 
 namespace mbgl {
 namespace platform {
 
+#if !defined(MBGL_USE_BUILTIN_ICU)
 std::string formatNumber(double number,
                          const std::string& localeId,
                          const std::string& currency,
@@ -22,28 +28,21 @@ std::string formatNumber(double number,
                    .unit(icu::CurrencyUnit(ucurrency.getBuffer(), status))
                    .locale(locale)
                    .formatDouble(number, status)
-#if U_ICU_VERSION_MAJOR_NUM >= 62
                    .toString(status);
-#else
-                   .toString();
-#endif
     } else {
         ustr = icu::number::NumberFormatter::with()
-#if U_ICU_VERSION_MAJOR_NUM >= 62
                    .precision(icu::number::Precision::minMaxFraction(minFractionDigits, maxFractionDigits))
-#else
-                   .rounding(icu::number::Rounder::minMaxFraction(minFractionDigits, maxFractionDigits))
-#endif
                    .locale(locale)
                    .formatDouble(number, status)
-#if U_ICU_VERSION_MAJOR_NUM >= 62
                    .toString(status);
-#else
-                   .toString();
-#endif
     }
     return ustr.toUTF8String(formatted);
 }
+#else
+std::string formatNumber(double number, const std::string&, const std::string&, uint8_t, uint8_t) {
+    return std::to_string(number);
+}
+#endif
 
 } // namespace platform
 } // namespace mbgl

platform/linux/linux.cmake

@@ -1,6 +1,6 @@
 find_package(CURL REQUIRED)
-find_package(ICU REQUIRED i18n)
-find_package(ICU REQUIRED uc)
+find_package(ICU OPTIONAL_COMPONENTS i18n)
+find_package(ICU OPTIONAL_COMPONENTS uc)
 find_package(JPEG REQUIRED)
 find_package(OpenGL REQUIRED GLX)
 find_package(PNG REQUIRED)
@@ -65,6 +65,20 @@ target_include_directories(
 include(${PROJECT_SOURCE_DIR}/vendor/nunicode.cmake)
 include(${PROJECT_SOURCE_DIR}/vendor/sqlite.cmake)
 
+if(NOT ${ICU_FOUND} OR "${ICU_VERSION}" VERSION_LESS 62.0)
+    message("-- ICU not found or too old, using builtin.")
+
+    set(MBGL_USE_BUILTIN_ICU TRUE)
+    include(${PROJECT_SOURCE_DIR}/vendor/icu.cmake)
+
+    set_source_files_properties(
+        ${PROJECT_SOURCE_DIR}/platform/default/src/mbgl/i18n/number_format.cpp
+        PROPERTIES
+        COMPILE_DEFINITIONS
+        MBGL_USE_BUILTIN_ICU
+    )
+endif()
+
 target_link_libraries(
     mbgl-core
     PRIVATE
@@ -72,8 +86,9 @@ target_link_libraries(
         ${JPEG_LIBRARIES}
         ${LIBUV_LIBRARIES}
         ${X11_LIBRARIES}
-        ICU::i18n
-        ICU::uc
+        $<$<NOT:$<BOOL:${MBGL_USE_BUILTIN_ICU}>>:ICU::i18n>
+        $<$<NOT:$<BOOL:${MBGL_USE_BUILTIN_ICU}>>:ICU::uc>
+        $<$<BOOL:${MBGL_USE_BUILTIN_ICU}>:mbgl-vendor-icu>
         OpenGL::GLX
         PNG::PNG
         mbgl-vendor-nunicode