ci: extract installing clang into a script

Author: pietroalbini

src/ci/azure-pipelines/steps/install-clang.yml

@@ -57,7 +57,11 @@ steps:
   displayName: Install sccache
   condition: and(succeeded(), not(variables.SKIP_JOB))
 
-- template: install-clang.yml
+- bash: src/ci/scripts/install-clang.sh
+  env:
+    AGENT_OS: $(Agent.OS)
+  displayName: Install clang
+  condition: and(succeeded(), not(variables.SKIP_JOB))
 
 # Switch to XCode 9.3 on OSX since it seems to be the last version that supports
 # i686-apple-darwin. We'll eventually want to upgrade this and it will probably

src/ci/azure-pipelines/steps/run.yml

@@ -0,0 +1,42 @@
+#!/bin/bash
+# This script installs clang on the local machine. Note that we don't install
+# clang on Linux since its compiler story is just so different. Each container
+# has its own toolchain configured appropriately already.
+
+set -euo pipefail
+IFS=$'\n\t'
+
+source "$(cd "$(dirname "$0")" && pwd)/../shared.sh"
+
+if isMacOS; then
+    curl -f https://rust-lang-ci-mirrors.s3-us-west-1.amazonaws.com/rustc/clang%2Bllvm-7.0.0-x86_64-apple-darwin.tar.xz | tar xJf -
+
+    ciCommandSetEnv CC "$(pwd)/clang+llvm-7.0.0-x86_64-apple-darwin/bin/clang"
+    ciCommandSetEnv CXX "$(pwd)/clang+llvm-7.0.0-x86_64-apple-darwin/bin/clang++"
+
+    # Configure `AR` specifically so rustbuild doesn't try to infer it as
+    # `clang-ar` by accident.
+    ciCommandSetEnv AR "ar"
+elif isWindows; then
+    # If we're compiling for MSVC then we, like most other distribution builders,
+    # switch to clang as the compiler. This'll allow us eventually to enable LTO
+    # amongst LLVM and rustc. Note that we only do this on MSVC as I don't think
+    # clang has an output mode compatible with MinGW that we need. If it does we
+    # should switch to clang for MinGW as well!
+    #
+    # Note that the LLVM installer is an NSIS installer
+    #
+    # Original downloaded here came from
+    # http://releases.llvm.org/7.0.0/LLVM-7.0.0-win64.exe
+    # That installer was run through `wine` on Linux and then the resulting
+    # installation directory (found in `$HOME/.wine/drive_c/Program Files/LLVM`) was
+    # packaged up into a tarball. We've had issues otherwise that the installer will
+    # randomly hang, provide not a lot of useful information, pollute global state,
+    # etc. In general the tarball is just more confined and easier to deal with when
+    # working with various CI environments.
+
+    mkdir -p citools
+    cd citools
+    curl -f "${MIRRORS_BASE}/LLVM-7.0.0-win64.tar.gz" | tar xzf -
+    ciCommandSetEnv RUST_CONFIGURE_ARGS "${RUST_CONFIGURE_ARGS} --set llvm.clang-cl=$(pwd)/clang-rust/bin/clang-cl.exe"
+fi

src/ci/scripts/install-clang.sh

@@ -55,3 +55,14 @@ function ciCommandAddPath {
 
     echo "##vso[task.prependpath]${path}"
 }
+
+function ciCommandSetEnv {
+    if [[ $# -ne 2 ]]; then
+        echo "usage: $0 <name> <value>"
+        exit 1
+    fi
+    name="$1"
+    value="$2"
+
+    echo "##vso[task.setvariable variable=${name}]${value}"
+}