@jheinen noticed in Fastest way to draw on Gtk.jl 'canvas' with plots produced from Plots.jl? - #12 by jheinen that Homebrew is installed automatically as a dependency even if running in Linux OS.
I tested this with a fresh installation (removed .julia):
julia> versioninfo()
Julia Version 1.2.0
Commit c6da87ff4b (2019-08-20 00:03 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: Intel(R) Core(TM) i7-2860QM CPU @ 2.50GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-6.0.1 (ORCJIT, sandybridge)
(v1.2) pkg> add GR Cairo Gtk
Cloning default registries into `~/.julia`
Cloning registry from "https://github.com/JuliaRegistries/General.git"
Added registry `General` to `~/.julia/registries/General`
Resolving package versions...
Installed HTTPClient ──────── v0.2.1
Installed URIParser ───────── v0.4.0
Installed Libz ────────────── v1.0.0
Installed BinaryProvider ──── v0.5.6
Installed Gtk ─────────────── v0.17.0
Installed Colors ──────────── v0.9.6
Installed Reexport ────────── v0.2.0
Installed WinRPM ──────────── v0.4.2
Installed Homebrew ────────── v0.7.1
Installed Compat ──────────── v2.1.0
Installed FixedPointNumbers ─ v0.6.1
Installed Parsers ─────────── v0.3.7
Installed Graphics ────────── v0.4.0
Installed JSON ────────────── v0.21.0
Installed NaNMath ─────────── v0.3.2
Installed Cairo ───────────── v0.6.0
Installed LibCURL ─────────── v0.5.2
Installed BufferedStreams ─── v1.0.0
Installed BinDeps ─────────── v0.8.10
Installed ColorTypes ──────── v0.8.0
Installed LibExpat ────────── v0.5.0
Installed GR ──────────────── v0.41.0
Updating `~/.julia/environments/v1.2/Project.toml`
[159f3aea] + Cairo v0.6.0
[28b8d3ca] + GR v0.41.0
[4c0ca9eb] + Gtk v0.17.0
Updating `~/.julia/environments/v1.2/Manifest.toml`
[9e28174c] + BinDeps v0.8.10
[b99e7846] + BinaryProvider v0.5.6
[e1450e63] + BufferedStreams v1.0.0
[159f3aea] + Cairo v0.6.0
[3da002f7] + ColorTypes v0.8.0
[5ae59095] + Colors v0.9.6
[34da2185] + Compat v2.1.0
[53c48c17] + FixedPointNumbers v0.6.1
[28b8d3ca] + GR v0.41.0
[a2bd30eb] + Graphics v0.4.0
[4c0ca9eb] + Gtk v0.17.0
[0862f596] + HTTPClient v0.2.1
[d9be37ee] + Homebrew v0.7.1
[682c06a0] + JSON v0.21.0
[b27032c2] + LibCURL v0.5.2
[522f3ed2] + LibExpat v0.5.0
[2ec943e9] + Libz v1.0.0
[77ba4419] + NaNMath v0.3.2
[69de0a69] + Parsers v0.3.7
[189a3867] + Reexport v0.2.0
[30578b45] + URIParser v0.4.0
[c17dfb99] + WinRPM v0.4.2
[2a0f44e3] + Base64
[ade2ca70] + Dates
[8bb1440f] + DelimitedFiles
[8ba89e20] + Distributed
[b77e0a4c] + InteractiveUtils
[76f85450] + LibGit2
[8f399da3] + Libdl
[37e2e46d] + LinearAlgebra
[56ddb016] + Logging
[d6f4376e] + Markdown
[a63ad114] + Mmap
[44cfe95a] + Pkg
[de0858da] + Printf
[3fa0cd96] + REPL
[9a3f8284] + Random
[ea8e919c] + SHA
[9e88b42a] + Serialization
[1a1011a3] + SharedArrays
[6462fe0b] + Sockets
[2f01184e] + SparseArrays
[10745b16] + Statistics
[8dfed614] + Test
[cf7118a7] + UUIDs
[4ec0a83e] + Unicode
Building GR ──────→ `~/.julia/packages/GR/ZI5OE/deps/build.log`
Building LibCURL ─→ `~/.julia/packages/LibCURL/lWJxD/deps/build.log`
Building WinRPM ──→ `~/.julia/packages/WinRPM/Y9QdZ/deps/build.log`
Building Homebrew → `~/.julia/packages/Homebrew/s09IX/deps/build.log`
Building Cairo ───→ `~/.julia/packages/Cairo/p68X8/deps/build.log`
Building Gtk ─────→ `~/.julia/packages/Gtk/aP55V/deps/build.log`
Is this intentional (why?) or a bug?