# Why does it always recompile a package?

**URL:** <https://discourse.julialang.org/t/why-does-it-always-recompile-a-package/131037>\
**Category:** General Usage\
**Tags:** compilation, precompilation\
**Created:** [July 25, 2025, 12:12am UTC](https://discourse.julialang.org/t/why-does-it-always-recompile-a-package/131037 "2025-07-25T00:12:17Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Kirby\_Zhang](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kirby_zhang/32/36204_2.png) [@Kirby\_Zhang](https://discourse.julialang.org/u/Kirby_Zhang)\
**Post date:** [July 25, 2025, 12:12am UTC](https://discourse.julialang.org/t/why-does-it-always-recompile-a-package/131037/1 "2025-07-25T00:12:17Z")

</div>

I have a locally developed package `Inherit.jl`. It has a ` __precompile__ (true)` statement. When I open the package project, importing it **does not** show any compilation time:

```julia-auto
K:\DevDocuments\fourthwave\pkg\Inherit>more Manifest.toml
# This file is machine-generated - editing it directly is not advised

julia_version = "1.10.10"
manifest_format = "2.0"
project_hash = "ae8820c6ea01bd8b2e229ea098dee154477e55fe"

[[deps.MacroTools]]
git-tree-sha1 = "1e0228a030642014fe5cfe68c2c0a818f9e3f522"
uuid = "1914dd2f-81c6-5fcd-8719-6d5c9610ff09"
version = "0.5.16"

K:\DevDocuments\fourthwave\pkg\Inherit>julia --project -e "@time import Inherit"
  0.008992 seconds (10.12 k allocations: 2.091 MiB)

K:\DevDocuments\fourthwave\pkg\Inherit>julia --project -e "@time import Inherit"
  0.008357 seconds (10.12 k allocations: 2.091 MiB)

```

But when importing the same package from another project, which only contains `Inherit.jl`, it always shows compilation time, and in fact loads slower (but without allocating more memory?):

```julia-auto
K:\DevDocuments\fourthwave\pkg>more Manifest.toml
# This file is machine-generated - editing it directly is not advised

julia_version = "1.10.10"
manifest_format = "2.0"
project_hash = "c72befabb43ba325ce509143141e3a1ffe8b0b9a"

[[deps.Inherit]]
deps = ["MacroTools"]
path = "Inherit"
uuid = "341b8389-5eed-42ab-a01e-622c6bedf032"
version = "0.2.0"

    [deps.Inherit.extensions]
    TestExt = "Test"

    [deps.Inherit.weakdeps]
    Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"

[[deps.MacroTools]]
git-tree-sha1 = "1e0228a030642014fe5cfe68c2c0a818f9e3f522"
uuid = "1914dd2f-81c6-5fcd-8719-6d5c9610ff09"
version = "0.5.16"

K:\DevDocuments\fourthwave\pkg>julia --project -e "@time import Inherit"
  0.013090 seconds (10.27 k allocations: 2.096 MiB, 37.25% compilation time)

K:\DevDocuments\fourthwave\pkg>julia --project -e "@time import Inherit"
  0.013046 seconds (10.27 k allocations: 2.096 MiB, 38.16% compilation time)

```

The manifests look the same to me. What could be happening?

---

<div class="post-metadata">

**Author:** ![Kirby\_Zhang](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kirby_zhang/32/36204_2.png) [@Kirby\_Zhang](https://discourse.julialang.org/u/Kirby_Zhang)\
**Post date:** [July 25, 2025, 12:26am UTC](https://discourse.julialang.org/t/why-does-it-always-recompile-a-package/131037/2 "2025-07-25T00:26:01Z")

</div>

`Inherit.jl` contains a TestExt package extension. When extension is loaded, the difference in load times between the two projects is even larger:

```julia-auto
K:\DevDocuments\fourthwave\pkg\Inherit>julia --project -e "@time import Test"
  0.020310 seconds (36.41 k allocations: 4.382 MiB)

K:\DevDocuments\fourthwave\pkg\Inherit>julia --project -e "@time begin import Test, Inherit end"
  0.027284 seconds (46.56 k allocations: 5.289 MiB)

K:\DevDocuments\fourthwave\pkg\Inherit>julia --project -e "@time begin import Inherit, Test end"
  0.025016 seconds (46.57 k allocations: 5.352 MiB)

```

vs

```julia-auto
K:\DevDocuments\fourthwave\pkg>julia --project -e "@time import Test"
  0.017926 seconds (36.33 k allocations: 4.375 MiB)

K:\DevDocuments\fourthwave\pkg>julia --project -e "@time begin import Test, Inherit end"
  0.043615 seconds (133.40 k allocations: 11.632 MiB, 35.19% compilation time)

K:\DevDocuments\fourthwave\pkg>julia --project -e "@time begin import Inherit, Test end"
  0.040809 seconds (133.60 k allocations: 11.643 MiB, 35.76% compilation time)

```

I believe this is indeed caused by extension mechanism. I have a pre-extension version of `Inherit.jl` and it doesn’t exhibit this behavior.

I was able to reproduce the issue from this MWE [itsdfish/PackageExtensionsExample.jl: A minimum working example of a package extension in Julia.](https://github.com/itsdfish/PackageExtensionsExample.jl)

```julia-auto
K:\DevDocuments\PackageExtensionsExample.jl>julia +1.11 --project -e "@time import PackageExtensionsExample"
  0.001460 seconds (1.20 k allocations: 84.116 KiB)

K:\DevDocuments\PackageExtensionsExample.jl>julia +1.11 --project -e "@time import PackageExtensionsExample"
  0.001321 seconds (1.20 k allocations: 84.069 KiB)

K:\DevDocuments\PackageExtensionsExample.jl>cd ..

K:\DevDocuments>julia +1.11 --project -e "@time import PackageExtensionsExample"
  0.006718 seconds (2.46 k allocations: 150.663 KiB, 41.72% compilation time)

K:\DevDocuments>julia +1.11 --project -e "@time import PackageExtensionsExample"
  0.004149 seconds (2.46 k allocations: 150.694 KiB, 63.95% compilation time)

```

---

<div class="post-metadata">

**Author:** ![Kirby\_Zhang](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/kirby_zhang/32/36204_2.png) [@Kirby\_Zhang](https://discourse.julialang.org/u/Kirby_Zhang)\
**Post date:** [July 25, 2025, 1:11am UTC](https://discourse.julialang.org/t/why-does-it-always-recompile-a-package/131037/3 "2025-07-25T01:11:50Z")

</div>

Could be I’m reading too much into “compilation time”. It might not be the recompilation of package code, but compilation of methods to process the extension modules. For example:

```julia-auto
K:\DevDocuments>julia --banner=no --project
... 你好我在 K:\DevDocuments
... aliases: pn = propertynames
... utilities available: @history, @cls, cls()
julia> @time import Inherit
  0.013344 seconds (10.98 k allocations: 1.487 MiB, 36.63% compilation time)

julia> @time import PackageExtensionsExample
  0.003583 seconds (1.63 k allocations: 126.219 KiB)

julia>

K:\DevDocuments>julia --banner=no --project
... 你好我在 K:\DevDocuments
... aliases: pn = propertynames
... utilities available: @history, @cls, cls()
julia> @time import PackageExtensionsExample
  0.006131 seconds (2.48 k allocations: 181.250 KiB, 72.28% compilation time)

julia> @time import Inherit
  0.007673 seconds (10.13 k allocations: 1.419 MiB)

```

Both modules use the extension mechanism, only the first loaded module shows “compilation time”. 😁