@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 ββββββββ v0.2.1
Installed URIParser βββββββββ v0.4.0
Installed Libz ββββββββββββββ v1.0.0
Installed BinaryProvider ββββ v0.5.6
Installed Gtk βββββββββββββββ v0.17.0
Installed Colors ββββββββββββ v0.9.6
Installed Reexport ββββββββββ v0.2.0
Installed WinRPM ββββββββββββ v0.4.2
Installed Homebrew ββββββββββ v0.7.1
Installed Compat ββββββββββββ v2.1.0
Installed FixedPointNumbers β v0.6.1
Installed Parsers βββββββββββ v0.3.7
Installed Graphics ββββββββββ v0.4.0
Installed JSON ββββββββββββββ v0.21.0
Installed NaNMath βββββββββββ v0.3.2
Installed Cairo βββββββββββββ v0.6.0
Installed LibCURL βββββββββββ v0.5.2
Installed BufferedStreams βββ v1.0.0
Installed BinDeps βββββββββββ v0.8.10
Installed ColorTypes ββββββββ v0.8.0
Installed LibExpat ββββββββββ v0.5.0
Installed GR ββββββββββββββββ 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 βββββββ `~/.julia/packages/GR/ZI5OE/deps/build.log`
Building LibCURL ββ `~/.julia/packages/LibCURL/lWJxD/deps/build.log`
Building WinRPM βββ `~/.julia/packages/WinRPM/Y9QdZ/deps/build.log`
Building Homebrew β `~/.julia/packages/Homebrew/s09IX/deps/build.log`
Building Cairo ββββ `~/.julia/packages/Cairo/p68X8/deps/build.log`
Building Gtk ββββββ `~/.julia/packages/Gtk/aP55V/deps/build.log`
Is this intentional (why?) or a bug?