Move SkiaSharp C API (src/c) out of upstream :core into libSkiaSharp

[mattleibow]

Summary

Moves SkiaSharp's fork-owned C API shim (src/c/*.cpp + include/c/*.h) out of upstream Skia's :core GN target and into the skiasharp_build("SkiaSharp") target (libSkiaSharp). This cleanly separates "Skia stuff" (upstream) from "SkiaSharp stuff" (our shim), shrinks the fork diff in upstream-owned files, and permanently fixes a class of "lost public_define when upstream reshuffles :core deps" bugs.

Companion parent-repo PR: mono/SkiaSharp#4131 (bumps this submodule + updates the non-GN Apple/Tizen builds).

Motivation

In the m148 update, upstream commit 029229d8be ("Simplify gn typeface related deps") moved the :fontmgr_* targets off :core and onto :skia. Our src/c/sk_typeface.cpp selects the Linux default font manager behind #elif defined(SK_FONTMGR_FONTCONFIG_AVAILABLE) — a public_define emitted by :fontmgr_fontconfig. Because src/c was injected into :core (via skia_core_sources += [...] in gn/core.gni) and upstream dropped :fontmgr_fontconfig from :core's deps, the define vanished from our compile → sk_fontmgr_create_default() silently returned an empty font manager → 0 fonts on Linux.

skiasharp_build("SkiaSharp") already deps on :skia, which lists :fontmgr_fontconfig in its public_deps. GN propagates a dependency's public_config (carrying public_defines) transitively through public_deps. So compiling src/c in libSkiaSharp makes it automatically see SK_FONTMGR_FONTCONFIG_AVAILABLE, the fontconfig include path, and SkFontMgr_New_FontConfig — via one existing edge, with no :core patch.

Changes

gn/core.gni

• Removed the fork block skia_core_sources += [ "$_src/c/*.cpp" ... ] (all 40 src/c sources + sk_types_priv.h).
• Removed the matching skia_core_public_headers += [ "$_include/c/*.h" ] block.
• Result: :core no longer compiles or references any of our shim.

BUILD.gn

• skiasharp_build("SkiaSharp") now owns the src/c/*.cpp sources (alongside the existing src/xamarin/*.cpp), the include/c/*.h public headers, and explicit deps/public_deps for everything those files need to compile that previously arrived transitively via :core:
  • fontmgr targets via optional() (fontconfig/CoreText/DirectWrite/Android/FCI) so the right SK_FONTMGR_*_AVAILABLE defines reach sk_typeface.cpp per platform,
  • module deps modules/skottie, modules/skresources, modules/sksg for skottie_animation.cpp / skresources_resource_provider.cpp / sksg_invalidation_controller.cpp,
  • GPU headers for gr_context.cpp.
• Completed the C API public header list. The original gn/core.gni fork block never listed sk_linker.h, skottie_animation.h, skresources_resource_provider.h, or sksg_invalidation_controller.h, even though their .cpp are compiled. Now that :SkiaSharp is the GN owner of the C API surface, these four are added to public so the target metadata (and gn check) sees the full surface.
• Removed the two m148 :core fork workarounds that only existed because src/c compiled in :core: the GPU-defines block and the if (skia_enable_fontmgr_fontconfig) { deps += [ ":fontmgr_fontconfig" ] } block (the 029229d8be workaround). After the move :core no longer compiles sk_typeface.cpp, so it no longer needs the define.
• Added a warnings/deprecation guardrail to the SkiaSharp target. The skiasharp_build template bypasses Skia's skia_target_default_configs, so //gn/skia:warnings (and thus -Wall/-Wextra) never reached our sources — deprecated-API usage compiled silently on every GN platform and only surfaced on Tizen's hand-written -Werror build. Now the target adds //gn/skia:warnings for parity, plus a new :skiasharp_strict config (listed last so it wins over :warnings' -Wno-deprecated-declarations) that forces -Werror=deprecated-declarations (/we4996 on MSVC). Any future deprecated-Skia-API use in src/c now fails the build on every platform.

src/c/sk_path.cpp — deprecation fixes

• sk_pathop_tight_bounds: was calling the [[deprecated]] SkPathOps::TightBounds; now calls SkPath::computeTightBounds() directly (identical semantics).
• Migrated the four // DEPRECATED bool/out-param overloads to the new std::optional<SkPath> API, preserving the C API's write-to-result + return-bool contract: Op, Simplify, AsWinding, and SkOpBuilder::resolve.

Validation

• macOS arm64 (native): builds clean; real 7.3 MB dylib, 820 sk_* C API symbols, Metal symbols present.
• Linux x64 (Docker emulated): builds clean; fontconfig regression guard confirmed — non-empty default typeface, Fc* undefined symbols present in the .so (was 0 when broken).
• Deprecation guardrail proven: reverting the TightBounds fix makes the build fail with error: 'TightBounds' is deprecated [-Werror,-Wdeprecated-declarations]; restoring it builds clean.
• Tests: SkiaSharp.Tests.Console pass (the Linux font tests — SKTypefaceTest.DefaultIsNotEmpty, SKFontManagerTest, text measurement — are the key regression guard).

Notes

• No C API signature changes; no binding regeneration needed.
• This is the proper architectural fix that lets us drop the temporary m148 :core workarounds (done here).

[Copilot]

Pull request overview

This PR moves SkiaSharp’s fork-owned C API shim (src/c/*.cpp and include/c/*.h) out of upstream Skia’s :core target and into the skiasharp_build("SkiaSharp") target (libSkiaSharp), so the shim’s build inputs/defines come from SkiaSharp’s own GN dependency graph instead of upstream :core.

Changes:

• Removed SkiaSharp C API sources/headers from gn/core.gni so upstream :core no longer compiles or exports the shim.
• Updated BUILD.gn so skiasharp_build("SkiaSharp") owns the shim sources/headers, adds the needed deps, and adds a strict deprecation-as-error warnings config.
• Updated src/c/sk_path.cpp to use the newer std::optional pathops APIs and avoid deprecated SkPathOps::TightBounds.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/c/sk_path.cpp	Replaces deprecated pathops calls with std::optional-based APIs and computeTightBounds() logic.
gn/core.gni	Removes the fork block that injected SkiaSharp C shim headers/sources into upstream :core.
BUILD.gn	Moves shim sources/headers into skiasharp_build("SkiaSharp"), adds deps, and enforces deprecation warnings as errors for the shim.

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