Drop libevent (#385)

`libevent` is no longer a required dependency on any major platform. Since [release 1.15](https://crystal-lang.org/2025/01/09/1.15.0-released/index.html#lifetime-eventloop) (crystal-lang/crystal#14996) we're directly using the system selectors (epoll, kqueue) on Linux, macOS, and FreeBSD. Libevent is still supported, but it needs opt-in via a compile-time flag [`-Devloop=libevent`](https://crystal-lang.org/2024/11/05/lifetime-event-loop/#effects).

It's safe to assume that barely anyone uses that.
So we should be able to remove this library from our distribution artifacts, reducing dependencies and size.

With this change, libevent is still supported, but it's an optional dependency, and you have to install it explicitly if you want to use it.

We may want to use libevent in stdlib specs, so I'm adding it to the `-build` images.

Author: straight-shoota

docker/alpine.Dockerfile

@@ -5,7 +5,7 @@ ARG llvm_version=20
 RUN \
   apk add --update --no-cache --force-overwrite \
     # core dependencies
-    gcc gmp-dev libevent-static musl-dev pcre-dev pcre2-dev pcre2-static \
+    gcc gmp-dev musl-dev pcre-dev pcre2-dev pcre2-static \
     # stdlib dependencies
     gc-dev gc-static libxml2-dev libxml2-static openssl-dev openssl-libs-static tzdata yaml-static zlib-static xz-static \
     # dev tools
@@ -28,6 +28,6 @@ FROM runtime as build
 RUN \
   apk add --update --no-cache --force-overwrite \
     llvm${llvm_version}-dev llvm${llvm_version}-static \
-    g++ libffi-dev
+    libevent-static g++ libffi-dev
 
 CMD ["/bin/sh"]

docker/ubuntu.Dockerfile

@@ -8,7 +8,7 @@ RUN \
   apt-get update && \
   DEBIAN_FRONTEND=noninteractive \
   apt-get install -y tzdata gcc pkg-config libssl-dev libxml2-dev libyaml-dev libgmp-dev git make \
-                     libpcre3-dev libpcre2-dev libevent-dev libz-dev libgc-dev && \
+                     libpcre3-dev libpcre2-dev libz-dev libgc-dev && \
   apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 ARG crystal_targz
@@ -24,7 +24,7 @@ FROM runtime as build
 
 RUN \
   apt-get update && \
-  apt-get install -y build-essential llvm-${llvm_version} lld-${llvm_version} libedit-dev gdb libffi-dev && \
+  apt-get install -y build-essential llvm-${llvm_version} lld-${llvm_version} libedit-dev libevent-dev gdb libffi-dev && \
   apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
 
 RUN ln -sf /usr/bin/ld.lld-${llvm_version} /usr/bin/ld.lld

linux/Dockerfile

@@ -25,7 +25,7 @@ RUN apk add --no-cache \
       # Statically-compiled llvm
       llvm${llvm_version}-dev llvm${llvm_version}-static \
       # Static stdlib dependencies
-      gc-dev gc-static zlib-static yaml-static libxml2-static pcre2-dev pcre2-static libevent-static zstd-static \
+      gc-dev gc-static zlib-static yaml-static libxml2-static pcre2-dev pcre2-static zstd-static \
       # Static compiler dependencies
       libffi-dev \
       # Build tools

linux/Makefile

@@ -26,7 +26,6 @@ PREVIOUS_CRYSTAL_RELEASE_LINUX64_TARGZ ?= https://github.com/crystal-lang/crysta
 SHARDS_VERSION = v0.19.1
 GC_VERSION = v8.2.8
 LIBPCRE2_VERSION = 10.44
-LIBEVENT_VERSION = release-2.1.12-stable
 
 OUTPUT_DIR = build
 OUTPUT_BASENAME64 = $(OUTPUT_DIR)/crystal-$(CRYSTAL_VERSION)-$(PACKAGE_ITERATION)-linux-$(arch)
@@ -48,8 +47,7 @@ BUILD_ARGS64 = $(BUILD_ARGS_COMMON) \
                --build-arg gnu_target=$(arch)-unknown-linux-gnu
 
 BUILD_ARGS64_BUNDLED = $(BUILD_ARGS64) \
-               --build-arg libpcre2_version=$(LIBPCRE2_VERSION) \
-               --build-arg libevent_version=$(LIBEVENT_VERSION)
+               --build-arg libpcre2_version=$(LIBPCRE2_VERSION)
 
 .PHONY: all
 all: all64 ## Build all distribution tarballs [default]

linux/bundled.dockerfile

@@ -13,28 +13,15 @@ RUN curl -L https://github.com/PCRE2Project/pcre2/releases/download/pcre2-${libp
  && ./configure --disable-shared --disable-cpp --enable-jit --enable-utf --enable-unicode-properties \
  && make -j$(nproc)
 
-# build libevent
-
-FROM debian AS libevent
-ARG libevent_version
-RUN git clone https://github.com/libevent/libevent \
- && cd libevent \
- && git checkout ${libevent_version} \
- && ./autogen.sh \
- && ./configure --disable-shared --disable-openssl \
- && make -j$(nproc)
-
 FROM debian
 ARG crystal_version
 ARG package_iteration
 ARG libpcre2_version
-ARG libevent_version
 
 RUN mkdir -p /output/lib/crystal/lib/
 
 # Copy libraries
 COPY --from=libpcre2 pcre2-${libpcre2_version}/.libs/libpcre2-8.a /output/lib/crystal/
-COPY --from=libevent libevent/.libs/libevent.a libevent/.libs/libevent_pthreads.a /output/lib/crystal/
 
 # Create tarball
 RUN mv /output /crystal-${crystal_version}-${package_iteration} \

omnibus/config/software/crystal.rb

@@ -16,7 +16,6 @@
 dependency "pcre2"
 dependency "bdw-gc"
 dependency "llvm_bin" unless FIRST_RUN
-dependency "libevent"
 dependency "libffi"
 
 env = with_standard_compiler_flags(with_embedded_path(

omnibus/config/software/libevent.rb

@@ -44,7 +44,7 @@ The following are the suggested packages to be able to use the whole standard li
 
 ```
 $ sudo apt-get install gcc pkg-config git tzdata \
-                       libpcre2-dev libevent-dev libyaml-dev \
+                       libpcre2-dev libyaml-dev \
                        libgmp-dev libssl-dev libxml2-dev
 ```
 

snapcraft/README.md

@@ -14,7 +14,7 @@ if [ ! -f $SNAP_USER_COMMON/env-check-success ]; then
   The following are the suggested packages to be able to use the whole standard library capabilities.
 
     $ sudo apt-get install gcc pkg-config git tzdata \\
-                           libpcre2-dev libevent-dev libyaml-dev \\
+                           libpcre2-dev libyaml-dev \\
                            libgmp-dev libssl-dev libxml2-dev
 
   You can find more detailed information in: