stale_cachefile: handle if the expected cache file is missing (JuliaLang#55419)

Part of fixing JuliaLang/Pkg.jl#3984

Author: IanButterworth

base/loading.jl

@@ -3666,7 +3666,13 @@ end
                                           ignore_loaded::Bool=false, requested_flags::CacheFlags=CacheFlags(),
                                           reasons::Union{Dict{String,Int},Nothing}=nothing, stalecheck::Bool=true)
     # n.b.: this function does nearly all of the file validation, not just those checks related to stale, so the name is potentially unclear
-    io = open(cachefile, "r")
+    io = try
+        open(cachefile, "r")
+    catch ex
+        ex isa IOError || ex isa SystemError || rethrow()
+        @debug "Rejecting cache file $cachefile for $modkey because it could not be opened" isfile(cachefile)
+        return true
+    end
     try
         checksum = isvalid_cache_header(io)
         if iszero(checksum)

test/precompile.jl

@@ -597,6 +597,10 @@ precompile_test_harness(false) do dir
     @test Base.invokelatest(Baz.baz) === 1
     @test Baz === UseBaz.Baz
 
+    # should not throw if the cachefile does not exist
+    @test !isfile("DoesNotExist.ji")
+    @test Base.stale_cachefile("", "DoesNotExist.ji") === true
+
     # Issue #12720
     FooBar1_file = joinpath(dir, "FooBar1.jl")
     write(FooBar1_file,