Support ascend(err) (#380)

Julia now has the global REPL varible `err`, and it's nice to be
able to `ascend(err)`. This seems particularly handy for
debugging MethodErrors as `ascend`/`descend` make the
types visible.

Project.toml

@@ -1,7 +1,7 @@
 name = "Cthulhu"
 uuid = "f68482b8-f384-11e8-15f7-abe071a5a75f"
 authors = ["Valentin Churavy <[email protected]>"]
-version = "2.8.2"
+version = "2.8.3"
 
 [deps]
 CodeTracking = "da1fd8a2-8d9e-5ec2-8556-3022fb5608a2"

src/Cthulhu.jl

@@ -791,6 +791,7 @@ FoldingTrees.writeoption(buf::IO, data::Data, charsused::Int) = FoldingTrees.wri
 
 function ascend(term, mi; interp::AbstractInterpreter=NativeInterpreter(), kwargs...)
     root = treelist(mi)
+    root === nothing && return
     menu = TreeMenu(root)
     choice = menu.current
     while choice !== nothing

src/backedges.jl

@@ -66,7 +66,7 @@ const _emptybackedges = MethodInstance[]
 struct IPFrames
     sfs::Vector{StackTraces.StackFrame}
 end
-function buildframes(bt)
+function buildframes(bt::Vector{Union{Ptr{Nothing}, Base.InterpreterIP}})
     ipframes = IPFrames[]
     for ip in bt
         sfs = Base.StackTraces.lookup(ip)
@@ -78,6 +78,15 @@ function buildframes(bt)
     end
     return ipframes
 end
+function buildframes(st::Vector{StackTraces.StackFrame})
+    ipframes = IPFrames[]
+    for sf in st
+        mi = sf.linfo
+        isa(mi, Core.MethodInstance) || continue
+        push!(ipframes, IPFrames([sf]))
+    end
+    return ipframes
+end
 
 # Extension API
 backedges(mi::MethodInstance) = isdefined(mi, :backedges) ? mi.backedges : _emptybackedges
@@ -88,6 +97,7 @@ nextnode(mi, edge) = edge
 
 instance(sfs::Vector{StackTraces.StackFrame}) = isempty(sfs) ? CC.Timings.ROOTmi : sfs[end].linfo::MethodInstance # we checked this type condition within `buildframes`
 method(sfs::Vector{StackTraces.StackFrame}) = method(instance(sfs))
+backedges(sframes::Vector{StackTraces.StackFrame}) = (ret = sframes[2:end]; isempty(ret) ? () : (ret,))
 
 instance(ipframes::Vector{IPFrames}) = isempty(ipframes) ? CC.Timings.ROOTmi : instance(ipframes[1].sfs)
 backedges(ipframes::Vector{IPFrames}) = (ret = ipframes[2:end]; isempty(ret) ? () : (ret,))
@@ -131,3 +141,12 @@ end
 treelist!(::Node, ::IO, ::Nothing, ::AbstractString, ::Base.IdSet) = nothing
 
 treelist(bt::Vector{Union{Ptr{Nothing}, Base.InterpreterIP}}) = treelist(buildframes(bt))
+treelist(st::Vector{StackTraces.StackFrame}) = treelist(buildframes(st))
+function treelist(exstk::Base.ExceptionStack)
+    if length(exstk.stack) == 1
+        return treelist(exstk.stack[1].backtrace)
+    end
+    # Don't error to avoid trashing `Main.err`
+    @error "exception stack contains $(length(exstk.stack)) exceptions, pick one with `ascend(err.stack[i].backtrace)`"
+    return nothing
+end

src/callsite.jl

@@ -540,5 +540,6 @@ function maybe_callsite(info::MultiCallInfo, callee::MethodInstance)
     return false
 end
 maybe_callsite(info::PureCallInfo, mi::MethodInstance) = mi.specTypes <: Tuple{mapany(Core.Typeof ∘ unwrapconst, info.argtypes)...}
+maybe_callsite(info::RTCallInfo, mi::MethodInstance) = false
 
 unwrapconst(@nospecialize(arg)) = arg isa Core.Const ? arg.val : arg

test/test_terminal.jl

@@ -297,6 +297,51 @@ end
             write(in, 'q')
             wait(t)
         end
+        # With backtraces
+        bt = try
+            sum([])
+        catch e
+            catch_backtrace()
+        end
+        fake_terminal() do term, in, out, _
+            t = @async begin
+                @with_try_stderr out ascend(term, bt)
+            end
+            str = readuntil(out, 'v'; keep=true)
+            @test occursin(r"zero.*Type{Any}", str)
+            write(in, 'q')
+            wait(t)
+        end
+        # With stacktraces
+        st = try
+            sum([])
+        catch e
+            stacktrace(catch_backtrace())
+        end
+        fake_terminal() do term, in, out, _
+            t = @async begin
+                @with_try_stderr out ascend(term, st)
+            end
+            str = readuntil(out, 'v'; keep=true)
+            @test occursin(r"zero.*Type{Any}", str)
+            write(in, 'q')
+            wait(t)
+        end
+        # With ExceptionStack (e.g., REPL's global `err` variable)
+        exstk = try
+            sum([])
+        catch e
+            Base.ExceptionStack([(exception=e, backtrace=stacktrace(catch_backtrace()))])
+        end
+        fake_terminal() do term, in, out, _
+            t = @async begin
+                @with_try_stderr out ascend(term, exstk)
+            end
+            str = readuntil(out, 'v'; keep=true)
+            @test occursin(r"zero.*Type{Any}", str)
+            write(in, 'q')
+            wait(t)
+        end
     finally
         # Restore the previous settings
         for fn in fieldnames(Cthulhu.CthulhuConfig)