From b609aa4f66caaac843867d7dc30c414e2e6b62da Mon Sep 17 00:00:00 2001
From: Tim Holy <tim.holy@gmail.com>
Date: Sat, 27 Jun 2020 07:14:20 -0500
Subject: [PATCH 1/2] Specify interface for LibGit2 abstract types

This improves inference results for a number LibGit2 operations,
and reduces invalidations from methods (notably, `peel`) that operate
on the values extracted from these fields.
---
 stdlib/LibGit2/src/types.jl | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/stdlib/LibGit2/src/types.jl b/stdlib/LibGit2/src/types.jl
index 6276544100888..c94bc01acaaf0 100644
--- a/stdlib/LibGit2/src/types.jl
+++ b/stdlib/LibGit2/src/types.jl
@@ -966,11 +966,43 @@ function split_cfg_entry(ce::ConfigEntry)
 end
 
 # Abstract object types
+
+"""
+    AbstractGitObject
+
+`AbstractGitObject`s must obey the following interface:
+- `obj.owner`, if present, must be a `Union{Nothing,GitRepo,GitTree}`
+- `obj.ptr`, if present, must be a `Union{Ptr{Cvoid},Ptr{SignatureStruct}}`
+"""
 abstract type AbstractGitObject end
+
+function Base.getproperty(obj::AbstractGitObject, name::Symbol)
+    if name === :owner
+        return getfield(obj, :owner)::Union{Nothing,GitRepo,GitTree}
+    elseif name === :ptr
+        return getfield(obj, :ptr)::Union{Ptr{Cvoid},Ptr{SignatureStruct}}
+    else
+        return getfield(obj, name)
+    end
+end
+
 Base.isempty(obj::AbstractGitObject) = (obj.ptr == C_NULL)
 
+# `GitObject`s must obey the following interface:
+# - `obj.owner` must be a `GitRepo`
+# - `obj.ptr` must be a Ptr{Cvoid}
 abstract type GitObject <: AbstractGitObject end
 
+function Base.getproperty(obj::GitObject, name::Symbol)
+    if name === :owner
+        return getfield(obj, :owner)::GitRepo
+    elseif name === :ptr
+        return getfield(obj, :ptr)::Ptr{Cvoid}
+    else
+        return getfield(obj, name)
+    end
+end
+
 for (typ, owntyp, sup, cname) in [
     (:GitRepo,           nothing,                 :AbstractGitObject, :git_repository),
     (:GitConfig,         :(Union{GitRepo, Nothing}), :AbstractGitObject, :git_config),

From 9b0c0386b82825e10fc4720221b3259f3709edb9 Mon Sep 17 00:00:00 2001
From: Tim Holy <tim.holy@gmail.com>
Date: Mon, 13 Jul 2020 05:13:02 -0500
Subject: [PATCH 2/2] Explain the getproperty methods

---
 stdlib/LibGit2/src/types.jl | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/stdlib/LibGit2/src/types.jl b/stdlib/LibGit2/src/types.jl
index c94bc01acaaf0..fb76331c04e55 100644
--- a/stdlib/LibGit2/src/types.jl
+++ b/stdlib/LibGit2/src/types.jl
@@ -977,6 +977,10 @@ end
 abstract type AbstractGitObject end
 
 function Base.getproperty(obj::AbstractGitObject, name::Symbol)
+    # These type-assertions enforce the interface requirements above.
+    # They assist type-inference in cases where the compiler only knows that it
+    # has an `AbstractGitObject` without being certain about the concrete type.
+    # See detailed explanation in https://github.com/JuliaLang/julia/pull/36452.
     if name === :owner
         return getfield(obj, :owner)::Union{Nothing,GitRepo,GitTree}
     elseif name === :ptr