Add a test

Author: timholy

test/precompile.jl

@@ -738,7 +738,6 @@ end
 
 # method root provenance & external code caching
 precompile_test_harness("code caching") do dir
-    Bid = rootid(Base)
     Cache_module = :Cacheb8321416e8a3e2f1
     # Note: calling setindex!(::Dict{K,V}, ::Any, ::K) adds both compression and codegen roots
     write(joinpath(dir, "$Cache_module.jl"),
@@ -1068,6 +1067,45 @@ precompile_test_harness("code caching") do dir
     end
 end
 
+precompile_test_harness("precompiletools") do dir
+    PrecompileToolsModule = :PCTb8321416e8a3e2f1
+    write(joinpath(dir, "$PrecompileToolsModule.jl"),
+        """
+        module $PrecompileToolsModule
+            struct MyType
+                x::Int
+            end
+
+            function call_findfirst(x, list)
+                # call a method defined in Base by runtime dispatch
+                return findfirst(==(Base.inferencebarrier(x)), Base.inferencebarrier(list))
+            end
+
+            let
+                ccall(:jl_tag_newly_inferred_enable, Cvoid, ())
+                call_findfirst(MyType(2), [MyType(1), MyType(2), MyType(3)])
+                ccall(:jl_tag_newly_inferred_disable, Cvoid, ())
+            end
+        end
+        """
+    )
+    pkgid = Base.PkgId(string(PrecompileToolsModule))
+    @test !Base.isprecompiled(pkgid)
+    Base.compilecache(pkgid)
+    @test Base.isprecompiled(pkgid)
+    @eval using $PrecompileToolsModule
+    M = invokelatest(getfield, @__MODULE__, PrecompileToolsModule)
+    invokelatest() do
+        m = which(Tuple{typeof(findfirst), Base.Fix2{typeof(==), T}, Vector{T}} where T)
+        success = 0
+        for mi in Base.specializations(m)
+            sig = Base.unwrap_unionall(mi.specTypes)
+            success += sig.parameters[3] === Vector{M.MyType}
+        end
+        @test success == 1
+    end
+end
+
 precompile_test_harness("invoke") do dir
     InvokeModule = :Invoke0x030e7e97c2365aad
     CallerModule = :Caller0x030e7e97c2365aad