Fix docs for Experimental.@force_compile

[timholy]

Also adds a direct test (we didn't used to have one and I hadn't really yet worked out how to do this). Responding to #42379 (comment)

[timholy]

The doctest failure is surprising; does Documenter strip meta Exprs?

Since the same test is in test/ I am inclined to just strip the jldoctest, but I'll see if someone knows of an easy fix.

[JeffBezanson]

When the doctest is running the code, there is extra stuff in the stack, so "interpreter" is probably sneaking in there.

[timholy]

I just stripped the jldoctest. Should be good to go if tests pass.

[IanButterworth]

I think this caused a failure on MacOS here?
https://build.julialang.org/#/builders/26/builds/4880/steps/5/logs/stdio
https://build.julialang.org/#/builders/26/builds/4886

[DilumAluthge]

Revert PR: #42784

[IanButterworth]

For reference, the tests pass locally on my mac

julia> @test !occursin("interpreter", string(stacktrace(
           begin
               Base.Experimental.@force_compile
               backtrace()
           end, true)))
Test Passed
  Expression: !(occursin("interpreter", string(stacktrace(begin
                    #= REPL[56]:3 =# Base.Experimental.@force_compile
                    backtrace()
                end, true))))
   Evaluated: !(occursin("interpreter", "Base.StackTraces.StackFrame[top-level scope at Test.jl:460, jl_toplevel_eval_flex at toplevel.c:880, jl_toplevel_eval_flex at toplevel.c:833, jl_toplevel_eval_flex at toplevel.c:833, ijl_toplevel_eval at toplevel.c:898 [inlined], ijl_toplevel_eval_in at toplevel.c:948, eval at boot.jl:368 [inlined], eval_user_input(ast::Any, backend::REPL.REPLBackend) at REPL.jl:151, repl_backend_loop(backend::REPL.REPLBackend) at REPL.jl:245, start_repl_backend(backend::REPL.REPLBackend, consumer::Any) at REPL.jl:230, run_repl(repl::REPL.AbstractREPL, consumer::Any; backend_on_current_task::Bool) at REPL.jl:363, run_repl(repl::REPL.AbstractREPL, consumer::Any) at REPL.jl:350, _jl_invoke at gf.c:0 [inlined], ijl_apply_generic at gf.c:2437, (::Base.var\"#940#942\"{Bool, Bool, Bool})(REPL::Module) at client.jl:394, (::Base.var\"#940#942\"{Bool, Bool, Bool})(REPL::Module) at sys.dylib:?, _jl_invoke at gf.c:0 [inlined], ijl_apply_generic at gf.c:2437, jl_apply at julia.h:1773 [inlined], jl_f__call_latest at builtins.c:757, #invokelatest#2 at essentials.jl:718 [inlined], invokelatest at essentials.jl:716 [inlined], run_main_repl(interactive::Bool, quiet::Bool, banner::Bool, history_file::Bool, color_set::Bool) at client.jl:379, exec_options(opts::Base.JLOptions) at client.jl:309, _start() at client.jl:497, _start() at sys.dylib:?, _jl_invoke at gf.c:0 [inlined], ijl_apply_generic at gf.c:2437, jl_apply at julia.h:1773 [inlined], true_main at jlapi.c:562, jl_repl_entrypoint at jlapi.c:706]"))

julia> @test  occursin("interpreter", string(stacktrace(
           begin
               backtrace()
           end, true)))
Test Passed
  Expression: occursin("interpreter", string(stacktrace(begin
                backtrace()
            end, true)))
   Evaluated: occursin("interpreter", "Base.StackTraces.StackFrame[backtrace() at sys.dylib:?, _jl_invoke at gf.c:0 [inlined], ijl_apply_generic at gf.c:2437, jl_apply at julia.h:1773 [inlined], do_call at interpreter.c:126, eval_body at interpreter.c:0, eval_body at interpreter.c:522, jl_interpret_toplevel_thunk at interpreter.c:739, top-level scope at Test.jl:460, jl_toplevel_eval_flex at toplevel.c:889, jl_toplevel_eval_flex at toplevel.c:833, jl_toplevel_eval_flex at toplevel.c:833, ijl_toplevel_eval at toplevel.c:898 [inlined], ijl_toplevel_eval_in at toplevel.c:948, eval at boot.jl:368 [inlined], eval_user_input(ast::Any, backend::REPL.REPLBackend) at REPL.jl:151, repl_backend_loop(backend::REPL.REPLBackend) at REPL.jl:245, start_repl_backend(backend::REPL.REPLBackend, consumer::Any) at REPL.jl:230, run_repl(repl::REPL.AbstractREPL, consumer::Any; backend_on_current_task::Bool) at REPL.jl:363, run_repl(repl::REPL.AbstractREPL, consumer::Any) at REPL.jl:350, _jl_invoke at gf.c:0 [inlined], ijl_apply_generic at gf.c:2437, (::Base.var\"#940#942\"{Bool, Bool, Bool})(REPL::Module) at client.jl:394, (::Base.var\"#940#942\"{Bool, Bool, Bool})(REPL::Module) at sys.dylib:?, _jl_invoke at gf.c:0 [inlined], ijl_apply_generic at gf.c:2437, jl_apply at julia.h:1773 [inlined], jl_f__call_latest at builtins.c:757, #invokelatest#2 at essentials.jl:718 [inlined], invokelatest at essentials.jl:716 [inlined], run_main_repl(interactive::Bool, quiet::Bool, banner::Bool, history_file::Bool, color_set::Bool) at client.jl:379, exec_options(opts::Base.JLOptions) at client.jl:309, _start() at client.jl:497, _start() at sys.dylib:?, _jl_invoke at gf.c:0 [inlined], ijl_apply_generic at gf.c:2437, jl_apply at julia.h:1773 [inlined], true_main at jlapi.c:562, jl_repl_entrypoint at jlapi.c:706]")

julia> versioninfo()
Julia Version 1.8.0-DEV.806
Commit 471600eb0f* (2021-10-23 18:16 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin20.6.0)
  CPU: Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-12.0.1 (ORCJIT, skylake)
Environment:
  JULIA_NUM_THREADS = 6

[timholy]

Thanks for checking @IanButterworth; since I don't have a mac, that will save me some head-scratching. I would be tempted to just skip that test on a mac, but I think it will pay to be more careful than that. I'll submit a sequence of debugging commits as a draft to see if I can understand the failure.