Improve inference and add precompiles in ExprSplitter (#428)

These make a substantial contribution to reducing latency for Revise 3,
specifically in the area of handling atsign-require blocks.

Author: timholy

src/construct.jl

@@ -437,7 +437,7 @@ mutable struct ExprSplitter
     lnn::Union{LineNumberNode,Nothing}
 end
 function ExprSplitter(mod::Module, ex::Expr; lnn=nothing)
-    index = []
+    index = Int[]
     if ex.head === :block || ex.head === :toplevel
         push!(index, 1)
     end
@@ -474,14 +474,15 @@ function queuenext!(iter::ExprSplitter)
         # Find or create the module
         newname = ex.args[2]::Symbol
         if isdefined(mod, newname)
-            mod = getfield(mod, newname)
-            mod isa Module || throw(ErrorException("invalid redefinition of constant $(newname)"))
+            newmod = getfield(mod, newname)
+            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)
-                mod = Base.root_module(id)
+                mod = Base.root_module(id)::Module
             else
                 loc = firstline(ex)
-                mod = Core.eval(mod, Expr(:module, ex.args[1], ex.args[2], Expr(:block, loc, loc)))
+                mod = Core.eval(mod, Expr(:module, ex.args[1], ex.args[2], Expr(:block, loc, loc)))::Module
             end
         end
         # We've handled the module declaration, remove it and queue the body

src/precompile.jl

@@ -23,6 +23,8 @@ function _precompile_()
     @assert precompile(Tuple{Type{Frame}, Module, Expr})
     @assert precompile(Tuple{Type{ExprSplitter}, Module, Expr})
     # @assert precompile(Tuple{typeof(Core.kwfunc(ExprSplitter)), NamedTuple{(:lnn,),Tuple{LineNumberNode}}, typeof(ExprSplitter), Module, Expr})
+    @assert precompile(Tuple{typeof(queuenext!), ExprSplitter})
+    @assert precompile(Tuple{typeof(Base.iterate), ExprSplitter})  # won't entirely work, but any dependents might help
     @assert precompile(Tuple{typeof(prepare_framedata), FrameCode, Vector{Any}, SimpleVector, Bool})
     @assert precompile(Tuple{typeof(prepare_args), Any, Vector{Any}, Vector{Any}})
     @assert precompile(Tuple{typeof(prepare_call), Any, Vector{Any}})

src/utils.jl

@@ -233,12 +233,13 @@ Test whether expression `ex` is a `@doc` expression.
 function is_doc_expr(@nospecialize(ex))
     docsym = Symbol("@doc")
     if isexpr(ex, :macrocall)
+        ex::Expr
         a = ex.args[1]
         is_global_ref(a, Core, docsym) && return true
         isa(a, Symbol) && a == docsym && return true
         if isexpr(a, :.)
             mod, name = (a::Expr).args[1], (a::Expr).args[2]
-            return mod === :Core && isa(name, QuoteNode) && name.value == docsym
+            return mod === :Core && isa(name, QuoteNode) && name.value === docsym
         end
     end
     return false