Try harder to find __toplevel__ stdlibs in ExprSplitter (#447)

Revise has to be able to analyze code in modules that are not in
the namespace. It turns out that differences between how discovery
works in interactive mode (which implicitly widens the Manifest to
include all the stdlibs) and test-mode (which does not) have led to
the handling discovery of toplevel modules problematic for some time:
it turns out we've been constructing "shadow" modules of the same names
as these stdlibs. Some of the exclusions in Revise's `sigtest.jl` test
file reflect this.

This causes ExprSplitter to try harder to find modules from
`Base.__toplevel__`. When we can't resolve the name in the manifest,
we also check Base.loaded_modules and see if we can find something of
that name.

This fixes a bug that just manifested (but whose roots are old) for
Revise on nightly.

Author: timholy

src/construct.jl

@@ -483,7 +483,19 @@ function queuenext!(iter::ExprSplitter)
             newmod isa Module || throw(ErrorException("invalid redefinition of constant $(newname)"))
             mod = newmod
         else
-            if (id = Base.identify_package(mod, String(newname))) !== nothing && haskey(Base.loaded_modules, id)
+            newnamestr = String(newname)
+            id = Base.identify_package(mod, newnamestr)
+            # If we're in a test environment and Julia's internal stdlibs are not a declared dependency of the package,
+            # we might fail to find it. Try really hard to find it.
+            if id === nothing && mod === Base.__toplevel__
+                for loaded_id in keys(Base.loaded_modules)
+                    if loaded_id.name == newnamestr
+                        id = loaded_id
+                        break
+                    end
+                end
+            end
+            if id !== nothing && haskey(Base.loaded_modules, id)
                 mod = Base.root_module(id)::Module
             else
                 loc = firstline(ex)

test/toplevel.jl

@@ -251,6 +251,28 @@ module Namespace end
         Core.eval(Base, :(sin(x::Int) = sin(float(x))))    # fix the definition of `sin`
     end
 end
+# When retrospectively parsing through modules to analyze code, Julia's stdlibs pose a bit
+# of a namespace challenge too: we never want to redefine new modules with the same name.
+@testset "Namespace stdlibs" begin
+    # Get the "real" LibCURL_jll module (Julia 1.6 and higher)
+    modref = nothing
+    for (id, mod) in Base.loaded_modules
+        if id.name == "LibCURL_jll"
+            modref = mod
+            break
+        end
+    end
+    if modref !== nothing
+        # Now try to find it by splitting
+        exsplit = JuliaInterpreter.ExprSplitter(Base.__toplevel__, :(
+            baremodule LibCURL_jll
+            using Base
+            Base.Experimental.@compiler_options compile=min optimize=0 infer=false
+            end))
+        (mod1, ex1), state1 = iterate(exsplit)
+        @test mod1 === modref
+    end
+end
 
 # incremental interpretation solves world-age problems
 # Taken straight from Julia's test/tuple.jl