Inferrability: eliminate more Core.Box

These stem from julia#15276, i.e.,
https://docs.julialang.org/en/v1/manual/performance-tips/#man-performance-captured
They were identified by scanning all compiled MethodInstances with
hasbox in the newly-released MethodAnalysis 0.4.5.

Core.Box often causes "follow-on" inference problems,
but for these cases there were relatively few, which may be why
these didn't show up earlier during the Great Invalidation Hunt.
Still, there doesn't seem to be any particular reason not to fix them.

This doesn't eliminate all Core.Box cases from Base, but only a
handful remain. The most common remaining case stems from inner
functions calling themselves.

base/compiler/ssair/show.jl

@@ -629,8 +629,10 @@ function show_ir_stmt(io::IO, code::Union{IRCode, CodeInfo}, idx::Int, line_info
 
         @assert new_node_inst !== UNDEF # we filtered these out earlier
         show_type = should_print_ssa_type(new_node_inst)
-        with_output_color(:green, io) do io′
-            print_stmt(io′, node_idx, new_node_inst, used, maxlength_idx, false, show_type)
+        let maxlength_idx=maxlength_idx, show_type=show_type
+            with_output_color(:green, io) do io′
+                print_stmt(io′, node_idx, new_node_inst, used, maxlength_idx, false, show_type)
+            end
         end
 
         if new_node_type === UNDEF # try to be robust against errors

base/errorshow.jl

@@ -345,13 +345,15 @@ function showerror_ambiguous(io::IO, meth, f, args)
         sigfix = typeintersect(m.sig, sigfix)
     end
     if isa(unwrap_unionall(sigfix), DataType) && sigfix <: Tuple
-        if all(m->morespecific(sigfix, m.sig), meth)
-            print(io, "\nPossible fix, define\n  ")
-            Base.show_tuple_as_call(io, :function,  sigfix)
-        else
-            println(io)
-            print(io, "To resolve the ambiguity, try making one of the methods more specific, or ")
-            print(io, "adding a new method more specific than any of the existing applicable methods.")
+        let sigfix=sigfix
+            if all(m->morespecific(sigfix, m.sig), meth)
+                print(io, "\nPossible fix, define\n  ")
+                Base.show_tuple_as_call(io, :function,  sigfix)
+            else
+                println(io)
+                print(io, "To resolve the ambiguity, try making one of the methods more specific, or ")
+                print(io, "adding a new method more specific than any of the existing applicable methods.")
+            end
         end
     end
     nothing

base/shell.jl

@@ -211,8 +211,8 @@ function print_shell_escaped_posixly(io::IO, args::AbstractString...)
         first || print(io, ' ')
         # avoid printing quotes around simple enough strings
         # that any (reasonable) shell will definitely never consider them to be special
-        have_single = false
-        have_double = false
+        have_single::Bool = false
+        have_double::Bool = false
         function isword(c::AbstractChar)
             if '0' <= c <= '9' || 'a' <= c <= 'z' || 'A' <= c <= 'Z'
                 # word characters

base/weakkeydict.jl

@@ -129,10 +129,12 @@ function get!(default::Callable, wkh::WeakKeyDict{K}, key) where {K}
 end
 
 function getkey(wkh::WeakKeyDict{K}, kk, default) where K
-    k = lock(wkh) do
-        k = getkey(wkh.ht, kk, nothing)
-        k === nothing && return nothing
-        return k.value
+    k = let wkh=wkh
+        lock(wkh) do
+            k = getkey(wkh.ht, kk, nothing)
+            k === nothing && return nothing
+            return k.value
+        end
     end
     return k === nothing ? default : k::K
 end

stdlib/REPL/src/LineEdit.jl

@@ -1979,11 +1979,11 @@ function enter_prefix_search(s::MIState, p::PrefixHistoryPrompt, backward::Bool)
         pss.indent = state(s, parent).indent
         pss.mi = s
     end
-    pss = state(s, p)
+    pss_ = state(s, p)
     if backward
-        history_prev_prefix(pss, pss.histprompt.hp, pss.prefix)
+        history_prev_prefix(pss_, pss_.histprompt.hp, pss_.prefix)
     else
-        history_next_prefix(pss, pss.histprompt.hp, pss.prefix)
+        history_next_prefix(pss_, pss_.histprompt.hp, pss_.prefix)
     end
     nothing
 end