Print ::Mux.Closure instead of ::Mux.var""{...}

Replaces #140.

I rewrote this because I wanted us to correctly match the braces, which
isn't practical with Regex.

src/Mux.jl

@@ -23,6 +23,7 @@ using Hiccup
 
 include("lazy.jl")
 include("server.jl")
+include("backtrace_rewriting.jl")
 include("basics.jl")
 include("routing.jl")
 

src/backtrace_rewriting.jl

@@ -0,0 +1,79 @@
+"""
+    mux_showerror(io, exc, bt)
+
+`showerror(io, exc, bt)`, but simplify the printing of all those Mux closures.
+"""
+function mux_showerror(io, e, bt)
+  buf = IOBuffer()
+  showerror(buf, e, bt)
+  str = String(take!(buf))
+  write(io, rename_mux_closures(str))
+end
+
+"""
+    find_matching_index(str, idx, closing_char)
+
+Find the index in `str` of the matching `closing_char` for the opening character at `idx`, or `nothing` if there is no matching character.
+
+If there is a matching character, `str[idx:find_matching_index(str, idx, closing_char)]` will contain:
+
+- n opening characters, where 1 ≤ n
+- m closing characters, where 1 ≤ m ≤ n
+
+The interior opening and closing characters need not be balanced.
+
+# Examples
+
+```
+julia> find_closing_char("((()))", 1, ')')
+6
+
+julia> find_closing_char("Vector{Union{Int64, Float64}}()", 7, '}')
+29
+```
+"""
+function find_closing_char(str, idx, closing_char)
+  opening_char = str[idx]
+  open = 1
+  while open != 0 && idx < lastindex(str)
+    idx = nextind(str, idx)
+    char = str[idx]
+    if char == opening_char
+      open += 1
+    elseif char == closing_char
+      open -= 1
+    end
+  end
+  return open == 0 ? idx : nothing
+end
+
+"""
+    rename_mux_closures(str)
+
+Replace all anonymous "Mux.var" closures in `str` with "Mux.Closure" to make backtraces easier to read.
+"""
+function rename_mux_closures(str)
+  maybe_idx = findfirst(r"Mux\.var\"#\w+#\w+\"{", str)
+  if isnothing(maybe_idx)
+    return str
+  else
+    start_idx, brace_idx = extrema(maybe_idx)
+  end
+  maybe_idx = find_closing_char(str, brace_idx, '}')
+  if !isnothing(maybe_idx)
+    suffix = maybe_idx == lastindex(str) ? "" : str[nextind(str, maybe_idx):end]
+    str = str[1:prevind(str, start_idx)] * "Mux.Closure" * suffix
+    rename_mux_closures(str)
+  else
+    str
+  end
+end
+
+"""
+    Closure
+
+Mux doesn't really use this type, we just print `Mux.Closure` instead of `Mux.var"#1#2{Mux.var"#3#4"{...}}` in stacktraces to make them easier to read.
+"""
+struct Closure
+  Closure() = error("""Mux doesn't really use this type, we just print `Mux.Closure` instead of `Mux.var"#1#2{Mux.var"#3#4"{...}}` in stacktraces to make them easier to read.""")
+end

src/basics.jl

@@ -84,7 +84,7 @@ function basiccatch(app, req)
     println(io, "<h1>Internal Error</h1>")
     println(io, "<p>$(error_phrases[rand(1:length(error_phrases))])</p>")
     println(io, "<pre class=\"box\">")
-    showerror(io, e, catch_backtrace())
+    mux_showerror(io, e, catch_backtrace())
     println(io, "</pre>")
     return d(:status => 500, :body => codeunits(String(take!(io))))
   end
@@ -98,3 +98,12 @@ function stderrcatch(app, req)
     return d(:status => 500, :body => codeunits("Internal server error"))
   end
 end
+
+function prettierstderrcatch(app, req)
+  try
+    app(req)
+  catch e
+    mux_showerror(stderr, e, catch_backtrace())
+    return d(:status => 500, :body => codeunits("Internal server error"))
+  end
+end

test/runtests.jl

@@ -177,4 +177,22 @@ println("SSL/TLS")
   end
 end
 
+@testset "rename_mux_closures" begin
+  s1 = """
+    [4] prettystderrcatch(app::Mux.var"#1#2"{typeof(test), Mux.var"#1#2"{Mux.var"#5#6"{Mux.var"#33#34"{Vector{Any}}, Mux.var"#23#24"{String}}, Mux.var"#1#2"{Mux.var"#5#6"{Mux.var"#33#34"{Vector{SubString{String}}}, Mux.var"#1#2"{Mux.var"#5#6"{Mux.var"#37#38"{Float64}, Mux.var"#23#24"{String}}, Mux.var"#23#24"{String}}}, Mux.var"#1#2"{Mux.var"#5#6"{Mux.var"#33#34"{Vector{SubString{String}}}, var"#5#7"}, Mux.var"#1#2"{Mux.var"#21#22"{Mux.var"#25#26"{Symbol, Int64}}, Mux.var"#23#24"{String}}}}}}, req::Dict{Any, Any})"""
+  e1 = "[4] prettystderrcatch(app::Mux.Closure, req::Dict{Any, Any})"
+  @test Mux.rename_mux_closures(s1) == e1
+
+  s2 = """[21] (::Mux.var"#7#8"{Mux.App})(req::HTTP.Messages.Request)"""
+  e2 = """[21] (::Mux.Closure)(req::HTTP.Messages.Request)"""
+  @test Mux.rename_mux_closures(s2) == e2
+
+  # Replace multiple closures at once
+  @test Mux.rename_mux_closures(s1 * '\n' * s2) == e1 * '\n' * e2
+
+  # Leave malformed input alone
+  s3 = """gabble (::Mux.var"#7#8{ gabble"""
+  @test Mux.rename_mux_closures(s3) == s3
+end
+
 end