fix(packagebundler): filter out dangling symlinks (#143)

`cp` errors out in libuv when it encounters dangling symlinks and `follow_symlinks` is set to `true`. In this PR, instead of calling `cp` directly on the directory we walk the directory tree copying files one by one and ignoring dangling symlinks.

Author: nkottary

docs/src/internal.md

@@ -5,6 +5,7 @@
 ```@docs
 JuliaHub._PackageBundler.bundle
 JuliaHub._PackageBundler.path_filterer
+JuliaHub._PackageBundler.cp_skip_dangling_symlinks
 ```
 
 ## Index

src/PackageBundler/PackageBundler.jl

@@ -96,7 +96,7 @@ function bundle(dir; output="", force=false, allownoenv=false, verbose=true)::St
     # add the depot and such, and finally tar all that up.
     tmp_dir = mktempdir()
     output_dir = joinpath(tmp_dir, name)
-    cp(dir, output_dir; follow_symlinks=true)
+    cp_skip_dangling_symlinks(dir, output_dir)
     bundle_dir = joinpath(output_dir, ".bundle")
     mkpath(bundle_dir)
     # Bundle artifacts

src/PackageBundler/utils.jl

@@ -96,6 +96,30 @@ function get_bundleignore(file, top)
     return patterns, top
 end
 
+"""
+    cp_skip_dangling_symlinks(src, dst)
+
+Recursively copies the directory `src` to `dst`, mirroring the behaviour of
+`cp(src, dst; follow_symlinks=true)` but silently skipping any dangling symlinks
+(symlinks whose target does not exist) instead of erroring on them.
+"""
+function cp_skip_dangling_symlinks(src::AbstractString, dst::AbstractString)
+    mkpath(dst)
+    for entry in readdir(src)
+        src_entry = joinpath(src, entry)
+        dst_entry = joinpath(dst, entry)
+        if isdir(src_entry)
+            cp_skip_dangling_symlinks(src_entry, dst_entry)
+        elseif isfile(src_entry)
+            cp(src_entry, dst_entry; follow_symlinks=true)
+        elseif islink(src_entry)
+            # Dangling symlink: isfile/isdir follow symlinks so both return false for a
+            # dangling symlink, while islink uses lstat so it returns true.
+            @warn "Skipping dangling symlink" path = src_entry
+        end
+    end
+end
+
 """
     path_filterer(top)
 

test/packagebundler.jl

@@ -267,6 +267,40 @@ end
     end
 end
 
+@testset "cp_skip_dangling_symlinks" begin
+    mktempdir() do src
+        # Regular file
+        write(joinpath(src, "regular.txt"), "hello")
+        # Subdirectory with a nested file
+        mkdir(joinpath(src, "subdir"))
+        write(joinpath(src, "subdir", "nested.txt"), "world")
+        # Valid symlink to an existing file
+        symlink(joinpath(src, "regular.txt"), joinpath(src, "valid_link.txt"))
+        # Dangling symlink (target does not exist)
+        symlink(joinpath(src, "nonexistent.txt"), joinpath(src, "dangling_link.txt"))
+
+        dst = tempname()
+        @test_logs (:warn, r"dangling") match_mode = :any JuliaHub._PackageBundler.cp_skip_dangling_symlinks(
+            src, dst
+        )
+
+        # Regular files and nested files are copied
+        @test isfile(joinpath(dst, "regular.txt"))
+        @test read(joinpath(dst, "regular.txt"), String) == "hello"
+        @test isfile(joinpath(dst, "subdir", "nested.txt"))
+        @test read(joinpath(dst, "subdir", "nested.txt"), String) == "world"
+
+        # Valid symlink is dereferenced: content present, no symlink at dst
+        @test isfile(joinpath(dst, "valid_link.txt"))
+        @test !islink(joinpath(dst, "valid_link.txt"))
+        @test read(joinpath(dst, "valid_link.txt"), String) == "hello"
+
+        # Dangling symlink is silently skipped
+        @test !ispath(joinpath(dst, "dangling_link.txt"))
+        @test !islink(joinpath(dst, "dangling_link.txt"))
+    end
+end
+
 function bundle_and_file_listing(bundle_root_path::AbstractString)
     out = tempname()
     JuliaHub._PackageBundler.bundle(