fix some LibGit2 errors

base/libgit2/diff.jl

@@ -4,11 +4,11 @@
 function Base.cconvert(::Type{Ptr{DiffOptionsStruct}}, pathspecs::AbstractString)
     str_ref = Base.cconvert(Ref{Cstring}, [pathspecs])
     sa = StrArrayStruct(Base.unsafe_convert(Ref{Cstring}, str_ref), 1)
-    do_ref = Ref(DiffOptions(pathspec = sa))
+    do_ref = Ref(DiffOptionsStruct(pathspec = sa))
     do_ref, str_ref
 end
 function Base.unsafe_convert(::Type{Ptr{DiffOptionsStruct}}, rr::Tuple{Ref{DiffOptionsStruct}, Ref{Cstring}})
-    Base.unsafe_convert(Ptr{DiffOptionStruct}, first(rr))
+    Base.unsafe_convert(Ptr{DiffOptionsStruct}, first(rr))
 end
 
 
@@ -42,6 +42,6 @@ function Base.getindex(diff::GitDiff, i::Integer)
     delta_ptr = ccall((:git_diff_get_delta, :libgit2),
                       Ptr{DiffDelta},
                       (Ptr{Void}, Csize_t), diff.ptr, i-1)
-    delta_ptr == C_NULL && return nothing
+    delta_ptr == C_NULL && throw(BoundsError("Attempt to access $(count(diff))-element GitDiff at index $i"))
     return unsafe_load(delta_ptr)
 end

base/libgit2/libgit2.jl

@@ -75,18 +75,22 @@ end
 isdirty(repo::GitRepo, paths::AbstractString=""; cached::Bool=false) =
     isdiff(repo, Consts.HEAD_FILE, paths, cached=cached)
 
-""" git diff-index <treeish> [-- <path>]"""
+"""
+    LibGit2.isdiff(repo::GitRepo, treeish[, paths]; [cached=false])
+
+Checks if there are any differences between the tree specified by `treeish` and  working tree (if `cached=false`) or the index (if `cached=true`).
+
+See `git diff-index <treeish> [-- <path>]`
+"""
 function isdiff(repo::GitRepo, treeish::AbstractString, paths::AbstractString=""; cached::Bool=false)
     tree_oid = revparseid(repo, "$treeish^{tree}")
-    iszero(tree_oid) && return true
+    iszero(tree_oid) && return error("invalid treeish $treeish") # this can be removed by #20104
     result = false
     tree = get(GitTree, repo, tree_oid)
     try
-        diff = diff_tree(repo, tree, paths)
+        diff = diff_tree(repo, tree, paths, cached=cached)
         result = count(diff) > 0
         close(diff)
-    catch err
-        result = true
     finally
         close(tree)
     end

test/libgit2.jl

@@ -452,6 +452,36 @@ mktempdir() do dir
                 close(repo)
             end
         end
+
+        @testset "diff" begin
+            repo = LibGit2.GitRepo(cache_repo)
+            try
+                @test !LibGit2.isdirty(repo)
+                @test !LibGit2.isdiff(repo, "HEAD")
+                @test !LibGit2.isdirty(repo, cached=true)
+                @test !LibGit2.isdiff(repo, "HEAD", cached=true)
+                open(joinpath(cache_repo,test_file), "a") do f
+                    println(f, "zzzz")
+                end
+                @test LibGit2.isdirty(repo)
+                @test LibGit2.isdiff(repo, "HEAD")
+                @test !LibGit2.isdirty(repo, cached=true)
+                @test !LibGit2.isdiff(repo, "HEAD", cached=true)
+                LibGit2.add!(repo, test_file)
+                @test LibGit2.isdirty(repo)
+                @test LibGit2.isdiff(repo, "HEAD")
+                @test LibGit2.isdirty(repo, cached=true)
+                @test LibGit2.isdiff(repo, "HEAD", cached=true)
+                LibGit2.commit(repo, "zzz")
+                @test !LibGit2.isdirty(repo)
+                @test !LibGit2.isdiff(repo, "HEAD")
+                @test !LibGit2.isdirty(repo, cached=true)
+                @test !LibGit2.isdiff(repo, "HEAD", cached=true)
+            finally
+                close(repo)
+            end
+        end
+
     end
 
     @testset "Fetch from cache repository" begin