From 759b26b9a20e32ed3d4377c15066696e5c6ed148 Mon Sep 17 00:00:00 2001
From: Tim Holy <tim.holy@gmail.com>
Date: Sat, 2 Jan 2021 10:32:58 -0600
Subject: [PATCH] Add a convenience utility for locating the origin of methods

This can be handy when trying to figure out where some `var"#31#32"`
function was defined.
---
 src/Observables.jl | 20 ++++++++++++++++++++
 test/runtests.jl   | 28 ++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)

diff --git a/src/Observables.jl b/src/Observables.jl
index c1bfb44..afbaf43 100644
--- a/src/Observables.jl
+++ b/src/Observables.jl
@@ -439,4 +439,24 @@ include("flatten.jl")
 include("time.jl")
 include("macros.jl")
 
+# Look up the source location of `do` block Observable MethodInstances
+function methodlist(@nospecialize(ft::Type))
+    if ft <: OnUpdate
+        ft = Base.unwrap_unionall(Base.unwrap_unionall(ft).parameters[1])
+        if ft <: MapUpdater
+            ft = Base.unwrap_unionall(Base.unwrap_unionall(ft).parameters[1])
+        end
+    end
+    mt = ft.name.mt
+    ms = Method[]
+    Base.visit(mt) do m
+        push!(ms, m)
+    end
+    return Base.MethodList(ms, mt)
+end
+
+methodlist(mi::Core.MethodInstance) = methodlist(Base.unwrap_unionall(mi.specTypes).parameters[1])
+methodlist(obsf::ObserverFunction) = methodlist(obsf.f)
+methodlist(@nospecialize(f::Function)) = methodlist(typeof(f))
+
 end # module
diff --git a/test/runtests.jl b/test/runtests.jl
index 4a62208..c3a762f 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -336,3 +336,31 @@ end
     obs[] = 1
     @test obs_copy[] == 1
 end
+
+@testset "methodlist" begin
+    _only(list) = (@assert length(list) == 1; return list[1])  # `only` is avail in Julia 1.4+
+    obs = Observable(1)
+    obsf = on(obs) do x
+        x + 1
+    end
+    line1 = -2 + @__LINE__
+    obs2 = map(obs) do x
+        x + 1
+    end
+    line2 = -2 + @__LINE__
+    obsflist = onany(obs, 5) do x, y
+        x + y
+    end
+    line3 = -2 + @__LINE__
+    obsf2 = _only(obsflist)
+    m = _only(Observables.methodlist(obsf).ms)
+    @test occursin("runtests.jl:$line1", string(m))
+    m = _only(Observables.methodlist(obsf.f).ms)
+    @test occursin("runtests.jl:$line1", string(m))
+    m = _only(Observables.methodlist(obs.listeners[2]).ms)
+    @test occursin("runtests.jl:$line2", string(m))
+    m = _only(Observables.methodlist(obsf2).ms)
+    @test occursin("runtests.jl:$line3", string(m))
+    obsf3 = on(sqrt, obs)
+    @test Observables.methodlist(obsf3).mt.name === :sqrt
+end