make failure to precompile a method return a value instead of a unconditionally warn (JuliaLang#41447)

Author: KristofferC

base/loading.jl

@@ -1937,11 +1937,13 @@ function precompile(@nospecialize(f), args::Tuple)
     precompile(Tuple{Core.Typeof(f), args...})
 end
 
+const ENABLE_PRECOMPILE_WARNINGS = Ref(false)
 function precompile(argt::Type)
-    if ccall(:jl_compile_hint, Int32, (Any,), argt) == 0
+    ret = ccall(:jl_compile_hint, Int32, (Any,), argt) != 0
+    if !ret && ENABLE_PRECOMPILE_WARNINGS[]
         @warn "Inactive precompile statement" maxlog=100 form=argt _module=nothing _file=nothing _line=0
     end
-    true
+    return ret
 end
 
 precompile(include_package_for_output, (PkgId, String, Vector{String}, Vector{String}, Vector{String}, typeof(_concrete_dependencies), Nothing))

test/ambiguous.jl

@@ -66,7 +66,7 @@ end
 ## Other ways of accessing functions
 # Test that non-ambiguous cases work
 let io = IOBuffer()
-    @test @test_logs precompile(ambig, (Int, Int))
+    @test precompile(ambig, (Int, Int))
     cf = @eval @cfunction(ambig, Int, (Int, Int))
     @test ccall(cf, Int, (Int, Int), 1, 2) == 4
     @test length(code_lowered(ambig, (Int, Int))) == 1
@@ -75,7 +75,7 @@ end
 
 # Test that ambiguous cases fail appropriately
 let io = IOBuffer()
-    @test @test_logs (:warn,) precompile(ambig, (UInt8, Int))
+    @test !precompile(ambig, (UInt8, Int))
     cf = @eval @cfunction(ambig, Int, (UInt8, Int))  # test for a crash (doesn't throw an error)
     @test_throws(MethodError(ambig, (UInt8(1), Int(2)), get_world_counter()),
                  ccall(cf, Int, (UInt8, Int), 1, 2))