From 1f698552b6d8980913be62511673453e2011b9dd Mon Sep 17 00:00:00 2001
From: Ian Butterworth <i.r.butterworth@gmail.com>
Date: Wed, 2 Jun 2021 08:42:52 +0200
Subject: [PATCH] `invokelatest` converts (#35)

---
 src/ImageIO.jl | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/ImageIO.jl b/src/ImageIO.jl
index 31ade9f..0b3fad2 100644
--- a/src/ImageIO.jl
+++ b/src/ImageIO.jl
@@ -20,6 +20,22 @@ for FMT in (
 end
 @inline canonical_type(::Formatted{T}, data) where T = canonical_type(T(), data)
 
+function enforece_canonical_type(f, data)
+    AT = canonical_type(f, data)
+    # This may not be type stable if `AT` is not a concrete type,
+    # but it's not an issue for `load`; it can never be type stable.
+
+    # work around the invokelatest overhead with an eager type check
+    if data isa AT
+        return data
+    else
+        # the backend might provide its own convert method
+        # use invokelatest to avoid world age issues
+        # See issue #34
+        return Base.invokelatest(convert, AT, data)
+    end
+end
+
 ## PNGs
 
 const load_locker = Threads.ReentrantLock()
@@ -33,11 +49,11 @@ end
 
 function load(f::File{DataFormat{:PNG}}; kwargs...)
     data = Base.invokelatest(checked_import(idPNGFiles).load, f.filename, kwargs...)
-    return convert(canonical_type(f, data), data)
+    return enforece_canonical_type(f, data)
 end
 function load(s::Stream{DataFormat{:PNG}}; kwargs...)
     data = Base.invokelatest(checked_import(idPNGFiles).load, stream(s), kwargs...)
-    return convert(canonical_type(s, data), data)
+    return enforece_canonical_type(s, data)
 end
 
 function save(f::File{DataFormat{:PNG}}, image::S; kwargs...) where {T, S<:Union{AbstractMatrix, AbstractArray{T,3}}}
@@ -60,12 +76,12 @@ for NETPBMFORMAT in (:PBMBinary, :PGMBinary, :PPMBinary, :PBMText, :PGMText, :PP
     @eval begin
         function load(f::File{DataFormat{$(Expr(:quote,NETPBMFORMAT))}})
             data = Base.invokelatest(checked_import(idNetpbm).load, f)
-            return convert(canonical_type(f, data), data)
+            return enforece_canonical_type(f, data)
         end
 
         function load(s::Stream{DataFormat{$(Expr(:quote,NETPBMFORMAT))}})
             data = Base.invokelatest(checked_import(idNetpbm).load, s)
-            return convert(canonical_type(s, data), data)
+            return enforece_canonical_type(s, data)
         end
 
         function save(f::File{DataFormat{$(Expr(:quote,NETPBMFORMAT))}}, image::S; kwargs...) where {S<:AbstractMatrix}
@@ -82,11 +98,11 @@ end
 
 function load(f::File{DataFormat{:TIFF}}; kwargs...)
     data = Base.invokelatest(checked_import(idTiffImages).load, f.filename, kwargs...)
-    return convert(canonical_type(f, data), data)
+    return enforece_canonical_type(f, data)
 end
 function load(s::Stream{DataFormat{:TIFF}}; kwargs...)
     data = Base.invokelatest(checked_import(idTiffImages).load, stream(s), kwargs...)
-    return convert(canonical_type(s, data), data)
+    return enforece_canonical_type(s, data)
 end
 
 function save(f::File{DataFormat{:TIFF}}, image::S) where {T, S<:Union{AbstractMatrix, AbstractArray{T,3}}}