Meta: Lint for duplicate endpoint IDs

We currently have 16 endpoints. The IDs are typed by a human at creation time.
This check will detect with we ever use an endpoint ID twice.

Since the large irrelevant directories are ignored, this should be quick enough.

.travis.yml

@@ -40,6 +40,7 @@ script:
 - export SERENITY_ROOT="$(pwd)"
 - Meta/lint-shell-scripts.sh
 - Meta/lint-executable-resources.sh
+- Meta/lint-ipc-ids.sh
 - Meta/check-style.sh
 - cd Toolchain
 - TRY_USE_LOCAL_TOOLCHAIN=y ./BuildIt.sh

Meta/lint-ipc-ids.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+set -e pipefail
+
+script_path=$(cd -P -- "$(dirname -- "$0")" && pwd -P)
+cd "$script_path/.."
+
+ALL_ENDPOINTS=$(find \( -name Toolchain -o -name Build -o -name .git -o -name Ports \) -prune -o -name '*.ipc' -print0 | xargs -0 grep -P '^endpoint ' | sort -k4 -n)
+
+BAD_ENDPOINTS=$(echo "${ALL_ENDPOINTS}" | cut -d' ' -f4 | uniq -d)
+
+if [ -n "${BAD_ENDPOINTS}" ]
+then
+    echo "This is the full list of all endpoints:"
+    echo "${ALL_ENDPOINTS}"
+    echo "These endpoint IDs are duplicated:"
+    echo "${BAD_ENDPOINTS}"
+    exit 1
+fi