Use non-const libraries only on Musl systems with Julia v1.6

The non-`const` library variable generates worse code because of the presence of
a trampoline, but the non-`const` is really needed only for Musl-based systems.

.github/workflows/ci.yml

@@ -17,7 +17,7 @@ jobs:
           - "1.3"
           - "1.4"
           - "1.5"
-          - "^1.6.0-0"
+          - "1.6"
           - "nightly"
         os:
           - ubuntu-latest
@@ -38,7 +38,7 @@ jobs:
           version: ${{ matrix.julia-version }}
           arch: ${{ matrix.julia-arch }}
       - name: Cache artifacts
-        uses: actions/cache@v1
+        uses: actions/cache@v2
         env:
           cache-name: cache-artifacts
         with:

Project.toml

@@ -1,7 +1,7 @@
 name = "JLLWrappers"
 uuid = "692b3bcd-3c85-4b1f-b108-f13ce0eb3210"
 authors = ["Mosè Giordano", "Elliot Saba"]
-version = "1.3.0"
+version = "1.4.0"
 
 [deps]
 Preferences = "21216c6a-2e73-6563-6e65-726566657250"

src/JLLWrappers.jl

@@ -6,6 +6,7 @@ end
 
 if VERSION >= v"1.6.0-DEV"
     using Preferences
+    using Base.BinaryPlatforms
 end
 
 # We need to glue expressions together a lot

src/products/library_generators.jl

@@ -2,14 +2,15 @@ macro declare_library_product(product_name, product_soname)
     handle_name = Symbol(string(product_name, "_handle"))
     get_path_name = Symbol(string("get_", product_name, "_path"))
     path_name = Symbol(string(product_name, "_path"))
-    @static if VERSION < v"1.6.0-DEV"
+    @static if VERSION < v"1.6.0-DEV" || libc(HostPlatform()) != "musl"
         lib_declaration = quote
             # On Julia 1.5-, this must be `const` and must be the SONAME
             const $(product_name) = $(product_soname)
         end
     else
         lib_declaration = quote
             # On Julia 1.6+, this doesn't have to be `const`!  Thanks Jeff!
+            # But this is needed only for Musl-based platforms.
             $(product_name) = ""
         end
     end
@@ -28,11 +29,12 @@ macro declare_library_product(product_name, product_soname)
 end
 
 function init_new_library_product(product_name)
-    @static if VERSION < v"1.6.0-DEV"
+    @static if VERSION < v"1.6.0-DEV" || libc(HostPlatform()) != "musl"
         return nothing
     else
         return quote
             # Initialize non-const variable export with the path to this product
+            # for Musl-based platforms.
             global $(product_name) = $(Symbol(string(product_name, "_path")))
         end
     end