[Impeller] fix validation warning on iOS/macOS when compiling externa…

…l texture shader. (flutter#45080)

```
[VERBOSE-2:validation.cc(49)] Break on 'ImpellerValidationBreak' to inspect point of failure: Could not create render pipeline for TextureFillExternal Pipeline :Fragment input(s) `user(locn1)` mismatching vertex shader output type(s) or not written by vertex shader
```

Fixes flutter/flutter#133286
Fixes flutter/flutter#133268

impeller/entity/contents/content_context.cc

@@ -278,8 +278,6 @@ ContentContext::ContentContext(
       CreateDefaultPipeline<BlendPipeline>(*context_);
   texture_pipelines_[default_options_] =
       CreateDefaultPipeline<TexturePipeline>(*context_);
-  texture_external_pipelines_[default_options_] =
-      CreateDefaultPipeline<TextureExternalPipeline>(*context_);
   position_uv_pipelines_[default_options_] =
       CreateDefaultPipeline<PositionUVPipeline>(*context_);
   tiled_texture_pipelines_[default_options_] =
@@ -312,7 +310,13 @@ ContentContext::ContentContext(
       CreateDefaultPipeline<YUVToRGBFilterPipeline>(*context_);
   porter_duff_blend_pipelines_[default_options_] =
       CreateDefaultPipeline<PorterDuffBlendPipeline>(*context_);
-
+  // GLES only shader.
+#ifdef IMPELLER_ENABLE_OPENGLES
+  if (GetContext()->GetBackendType() == Context::BackendType::kOpenGLES) {
+    texture_external_pipelines_[default_options_] =
+        CreateDefaultPipeline<TextureExternalPipeline>(*context_);
+  }
+#endif  // IMPELLER_ENABLE_OPENGLES
   if (context_->GetCapabilities()->SupportsCompute()) {
     auto pipeline_desc =
         PointsComputeShaderPipeline::MakeDefaultPipelineDescriptor(*context_);

impeller/entity/contents/content_context.h

@@ -56,7 +56,6 @@
 #include "impeller/entity/sweep_gradient_fill.frag.h"
 #include "impeller/entity/texture_fill.frag.h"
 #include "impeller/entity/texture_fill.vert.h"
-#include "impeller/entity/texture_fill_external.frag.h"
 #include "impeller/entity/tiled_texture_fill.frag.h"
 #include "impeller/entity/uv.comp.h"
 #include "impeller/entity/vertices.frag.h"
@@ -112,6 +111,10 @@
 #include "impeller/entity/framebuffer_blend_screen.frag.h"
 #include "impeller/entity/framebuffer_blend_softlight.frag.h"
 
+#ifdef IMPELLER_ENABLE_OPENGLES
+#include "impeller/entity/texture_fill_external.frag.h"
+#endif  // IMPELLER_ENABLE_OPENGLES
+
 #if IMPELLER_ENABLE_3D
 #include "impeller/scene/scene_context.h"  // nogncheck
 #endif
@@ -151,8 +154,6 @@ using RRectBlurPipeline =
 using BlendPipeline = RenderPipelineT<BlendVertexShader, BlendFragmentShader>;
 using TexturePipeline =
     RenderPipelineT<TextureFillVertexShader, TextureFillFragmentShader>;
-using TextureExternalPipeline =
-    RenderPipelineT<TextureFillVertexShader, TextureFillExternalFragmentShader>;
 using PositionUVPipeline =
     RenderPipelineT<TextureFillVertexShader, TiledTextureFillFragmentShader>;
 using TiledTexturePipeline =
@@ -291,6 +292,11 @@ using FramebufferBlendSoftLightPipeline =
 using PointsComputeShaderPipeline = ComputePipelineBuilder<PointsComputeShader>;
 using UvComputeShaderPipeline = ComputePipelineBuilder<UvComputeShader>;
 
+#ifdef IMPELLER_ENABLE_OPENGLES
+using TextureExternalPipeline =
+    RenderPipelineT<TextureFillVertexShader, TextureFillExternalFragmentShader>;
+#endif  // IMPELLER_ENABLE_OPENGLES
+
 /// Pipeline state configuration.
 ///
 /// Each unique combination of these options requires a different pipeline state
@@ -428,10 +434,14 @@ class ContentContext {
     return GetPipeline(texture_pipelines_, opts);
   }
 
+#ifdef IMPELLER_ENABLE_OPENGLES
   std::shared_ptr<Pipeline<PipelineDescriptor>> GetTextureExternalPipeline(
       ContentContextOptions opts) const {
+    FML_DCHECK(GetContext()->GetBackendType() ==
+               Context::BackendType::kOpenGLES);
     return GetPipeline(texture_external_pipelines_, opts);
   }
+#endif  // IMPELLER_ENABLE_OPENGLES
 
   std::shared_ptr<Pipeline<PipelineDescriptor>> GetPositionUVPipeline(
       ContentContextOptions opts) const {
@@ -757,7 +767,9 @@ class ContentContext {
   mutable Variants<RRectBlurPipeline> rrect_blur_pipelines_;
   mutable Variants<BlendPipeline> texture_blend_pipelines_;
   mutable Variants<TexturePipeline> texture_pipelines_;
+#ifdef IMPELLER_ENABLE_OPENGLES
   mutable Variants<TextureExternalPipeline> texture_external_pipelines_;
+#endif  // IMPELLER_ENABLE_OPENGLES
   mutable Variants<PositionUVPipeline> position_uv_pipelines_;
   mutable Variants<TiledTexturePipeline> tiled_texture_pipelines_;
   mutable Variants<GaussianBlurAlphaDecalPipeline>

impeller/entity/contents/texture_contents.cc

@@ -155,11 +155,16 @@ bool TextureContents::Render(const ContentContext& renderer,
   }
   pipeline_options.primitive_type = PrimitiveType::kTriangleStrip;
 
+#ifdef IMPELLER_ENABLE_OPENGLES
   if (is_external_texture) {
     cmd.pipeline = renderer.GetTextureExternalPipeline(pipeline_options);
   } else {
     cmd.pipeline = renderer.GetTexturePipeline(pipeline_options);
   }
+#else
+  cmd.pipeline = renderer.GetTexturePipeline(pipeline_options);
+#endif  // IMPELLER_ENABLE_OPENGLES
+
   cmd.stencil_reference = entity.GetStencilDepth();
   cmd.BindVertices(vertex_builder.CreateVertexBuffer(host_buffer));
   VS::BindFrameInfo(cmd, host_buffer.EmplaceUniform(frame_info));

impeller/renderer/backend/metal/pipeline_library_mtl.mm

@@ -112,7 +112,8 @@
       ^(id<MTLRenderPipelineState> _Nullable render_pipeline_state,
         NSError* _Nullable error) {
         if (error != nil) {
-          VALIDATION_LOG << "Could not create render pipeline: "
+          VALIDATION_LOG << "Could not create render pipeline for "
+                         << descriptor.GetLabel() << " :"
                          << error.localizedDescription.UTF8String;
           promise->set_value(nullptr);
           return;