add script to prevent point releases with same number as existing ones

.github/workflows/ci.yml

@@ -128,6 +128,9 @@ jobs:
       - name: ensure backported commits are in upstream branches
         run: src/ci/scripts/verify-backported-commits.sh
         if: success() && !env.SKIP_JOB
+      - name: ensure the stable version number is correct
+        run: src/ci/scripts/verify-stable-version-number.sh
+        if: success() && !env.SKIP_JOB
       - name: run the build
         run: src/ci/scripts/run-build-from-ci.sh
         env:
@@ -502,6 +505,9 @@ jobs:
       - name: ensure backported commits are in upstream branches
         run: src/ci/scripts/verify-backported-commits.sh
         if: success() && !env.SKIP_JOB
+      - name: ensure the stable version number is correct
+        run: src/ci/scripts/verify-stable-version-number.sh
+        if: success() && !env.SKIP_JOB
       - name: run the build
         run: src/ci/scripts/run-build-from-ci.sh
         env:
@@ -612,6 +618,9 @@ jobs:
       - name: ensure backported commits are in upstream branches
         run: src/ci/scripts/verify-backported-commits.sh
         if: success() && !env.SKIP_JOB
+      - name: ensure the stable version number is correct
+        run: src/ci/scripts/verify-stable-version-number.sh
+        if: success() && !env.SKIP_JOB
       - name: run the build
         run: src/ci/scripts/run-build-from-ci.sh
         env:

src/ci/github-actions/ci.yml

@@ -206,6 +206,10 @@ x--expand-yaml-anchors--remove:
         run: src/ci/scripts/verify-backported-commits.sh
         <<: *step
 
+      - name: ensure the stable version number is correct
+        run: src/ci/scripts/verify-stable-version-number.sh
+        <<: *step
+
       - name: run the build
         run: src/ci/scripts/run-build-from-ci.sh
         env:

src/ci/scripts/verify-stable-version-number.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+# On the stable channel, check whether we're trying to build artifacts with the
+# same version number of a release that's already been published, and fail the
+# build if that's the case.
+#
+# It's a mistake whenever that happens: the release process won't start if it
+# detects a duplicate version number, and the artifacts would have to be
+# rebuilt anyway.
+
+set -euo pipefail
+IFS=$'\n\t'
+
+if [[ "$(cat src/ci/channel)" != "stable" ]]; then
+    echo "This script only works on the stable channel. Skipping the check."
+    exit 0
+fi
+
+version="$(cat src/version)"
+url="https://static.rust-lang.org/dist/channel-rust-${version}.toml"
+
+if curl --silent --fail "${url}" >/dev/null; then
+    echo "The version number ${version} matches an existing release."
+    echo
+    echo "If you're trying to prepare a point release, remember to change the"
+    echo "version number in the src/version file."
+    exit 1
+else
+    echo "The version number ${version} does not match any released version!"
+    exit 0
+fi