[core] Modularize FileSource codebase (#15768)

* [core] Introduce FileSourceManager and use it for default platform impl

  - Add `FileSourceManager` interface that provides access to `FileSource`
    instances and means of registering / unregistering `FileSource` factories
  - Split `DefaultFileSource` into smaller parts
  - Add `DatabaseFileSource` interface and it's default implementation
  - Remove inter-dependencies between concrete `FileSource` classes

* [build] Add files to next build system

* [core] Add generic property setters / getters

* [core] Remove setOnlineStatus from OnlineFileSource interface

* [core] Hide threading implementation details from DatabaseFileSource interface

* [core] Make DB file source methods virtual

* [core] Add documentation for DatabaseFileSource and rename one method

* [core] Use simple callback instead of ActorRef

* [core] Remove ActorRef from OnlineFileSource public header

* [core] Add callback to FileSource::forward async API

* [core] Pass OfflineRegionDefinition by value

* [core] Update tests to use modular file sources

* [core] Update unit tests

* [core] Update unit tests after rebase

* [core] Backport low prio fix for cached requests

* [core] Backport pack database

* [core] Return removed factory from unRegisterFileSourceFactory

* [core] Rename shadowed args in onlinefilesource

* [core] Remove simple std::function callback aliases

* [core] Expose online file source property keys in public header file

* [test-runner] Add proxy file source test runner

* [cache] Update mbgl-cache utility to use new file source

* [metrics] Rebaseline binary size metrics

* [offline] Update offline utility

* [core] Update changelog

2 files changed, 25 insertions, 3 deletions

diff --git a/src/mbgl/tile/geometry_tile.cpp b/src/mbgl/tile/geometry_tile.cpp
index 7df81fa30f..67e4459104 100644
--- a/src/mbgl/tile/geometry_tile.cpp
+++ b/src/mbgl/tile/geometry_tile.cpp
@@ -262,7 +262,9 @@ void GeometryTile::onGlyphsAvailable(GlyphMap glyphs) {
 }
 
 void GeometryTile::getGlyphs(GlyphDependencies glyphDependencies) {
-    glyphManager.getGlyphs(*this, std::move(glyphDependencies), *fileSource);
+    if (fileSource) {
+        glyphManager.getGlyphs(*this, std::move(glyphDependencies), *fileSource);
+    }
 }
 
 void GeometryTile::onImagesAvailable(ImageMap images, ImageMap patterns, ImageVersionMap versionMap, uint64_t imageCorrelationID) {
diff --git a/src/mbgl/tile/tile_loader_impl.hpp b/src/mbgl/tile/tile_loader_impl.hpp
index 7c02021083..51efbb99e9 100644
--- a/src/mbgl/tile/tile_loader_impl.hpp
+++ b/src/mbgl/tile/tile_loader_impl.hpp
@@ -1,12 +1,19 @@
 #pragma once
 
-#include <mbgl/tile/tile_loader.hpp>
-#include <mbgl/storage/file_source.hpp>
 #include <mbgl/renderer/tile_parameters.hpp>
+#include <mbgl/storage/file_source.hpp>
+#include <mbgl/tile/tile_loader.hpp>
+#include <mbgl/util/async_request.hpp>
 #include <mbgl/util/tileset.hpp>
 
 #include <cassert>
 
+namespace {
+inline std::exception_ptr getCantLoadTileError() {
+    return std::make_exception_ptr(std::runtime_error("Can't load tile."));
+}
+} // namespace
+
 namespace mbgl {
 
 template <typename T>
@@ -26,6 +33,11 @@ TileLoader<T>::TileLoader(T& tile_,
         Resource::LoadingMethod::CacheOnly)),
       fileSource(parameters.fileSource) {
     assert(!request);
+    if (!fileSource) {
+        tile.setError(getCantLoadTileError());
+        return;
+    }
+
     if (fileSource->supportsCacheOnlyRequests()) {
         // When supported, the first request is always optional, even if the TileLoader
         // is marked as required. That way, we can let the first optional request continue
@@ -49,6 +61,10 @@ TileLoader<T>::~TileLoader() = default;
 template <typename T>
 void TileLoader<T>::loadFromCache() {
     assert(!request);
+    if (!fileSource) {
+        tile.setError(getCantLoadTileError());
+        return;
+    }
 
     resource.loadingMethod = Resource::LoadingMethod::CacheOnly;
     request = fileSource->request(resource, [this](Response res) {
@@ -113,6 +129,10 @@ void TileLoader<T>::loadedData(const Response& res) {
 template <typename T>
 void TileLoader<T>::loadFromNetwork() {
     assert(!request);
+    if (!fileSource) {
+        tile.setError(getCantLoadTileError());
+        return;
+    }
 
     // Instead of using Resource::LoadingMethod::All, we're first doing a CacheOnly, and then a
     // NetworkOnly request.