From 0101903aa0401946fe1dbba9630accbde0bd6279 Mon Sep 17 00:00:00 2001
From: projectured <projectured@gmail.com>
Date: Mon, 14 Sep 2026 14:38:34 +0200
Subject: [PATCH] ensurecompiled: load the packages instead of precompiling
 them

`ensurecompiled` only has to leave a cache that the sysimage build can read.
That build runs with `--pkgimages=no`, so it needs the source-only cache, and
loading the packages writes it.

`Pkg.precompile()` reaches the same state, but under `--pkgimages=no` Pkg's own
native code is not available, so the first call in a process compiles Pkg's
precompile path from IR. `ensurecompiled` starts a fresh process every build,
so it pays that every time.

On `examples/MyApp` with a warm depot of 381 packages, all with
`--pkgimages=no`: `using Pkg; Pkg.precompile()` takes 28.7 s and 26.8 s on
repeat, `import MyApp` takes 0.6 s and 0.6 s. In one process the first
`Pkg.precompile()` costs 21.1 s and the second 0.0 s.

Assisted-by: Claude Code (Opus 5)
---
 src/PackageCompiler.jl | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/PackageCompiler.jl b/src/PackageCompiler.jl
index a5f48264..bba2cc75 100644
--- a/src/PackageCompiler.jl
+++ b/src/PackageCompiler.jl
@@ -497,8 +497,10 @@ end
 
 function ensurecompiled(project, packages, sysimage)
     length(packages) == 0 && return
-    # TODO: Only precompile `packages` (should be available in Pkg 1.8)
-    cmd = `$(get_julia_cmd()) --sysimage=$sysimage -e 'using Pkg; Pkg.precompile()'`
+    # `import` writes the source-only cache that the --pkgimages=no sysimage
+    # build needs. Pkg.precompile() would JIT-compile Pkg itself to do the same.
+    imports = join(("import " * String(package) for package in packages), "\n")
+    cmd = `$(get_julia_cmd()) --sysimage=$sysimage -e $imports`
     splitter = Sys.iswindows() ? ';' : ':'
     @debug "ensurecompiled: running $cmd" JULIA_LOAD_PATH = "$project$(splitter)@stdlib"
     cmd = addenv(cmd, "JULIA_LOAD_PATH" => "$project$(splitter)@stdlib")