Add PO file update check to tests

The PO file updates can now run in a normal test, eliminating the need for
special handling.

Rename the `check-translations.fish` script, to clarify which part of the checks
happens in it.

build_tools/check.sh

@@ -2,17 +2,25 @@
 
 set -ex
 
+cleanup () {
+  if [ -n "$template_file" ] && [ -e "$template_file" ]; then
+    rm "$template_file"
+  fi
+}
+
+trap cleanup EXIT INT TERM HUP
+
 RUSTFLAGS='-D warnings'; export RUSTFLAGS
 RUSTDOCFLAGS='-D warnings'; export RUSTDOCFLAGS
 
 repo_root="$(dirname "$0")/.."
 build_dir="$repo_root/target/debug"
 
-cargo build --workspace --all-targets
+template_file=$(mktemp)
+FISH_GETTEXT_EXTRACTION_FILE=$template_file cargo build --workspace --all-targets
 PATH="$build_dir:$PATH" "$repo_root/build_tools/style.fish" --all --check
 cargo clippy --workspace --all-targets
 cargo test --no-default-features --workspace --all-targets
 cargo test --doc --workspace
 cargo doc --workspace
-
-"$repo_root/tests/test_driver.py" "$build_dir"
+FISH_GETTEXT_EXTRACTION_FILE=$template_file "$repo_root/tests/test_driver.py" "$build_dir"

tests/checks/po-files-up-to-date.fish

@@ -0,0 +1,19 @@
+#RUN: fish=%fish %fish %s
+#REQUIRES: msguniq --help
+# Compiling in this test is too expensive.
+# We need the gettext template extracted from the Rust sources passed in via env var,
+# in order to pass it on.
+#REQUIRES: test -e "$FISH_GETTEXT_EXTRACTION_FILE"
+
+set -l dir (status dirname)
+
+# Ensure that fish is in $PATH for the translation scripts.
+set -lxp PATH (path dirname $fish)
+
+# Using cargo in this test is expensive because $HOME is changed,
+# so the entire toolchain needs to be downloaded and installed,
+# followed by a clean build of the repo.
+# The `--use-existing-template` argument allows using the pre-built version of the gettext template
+# file.
+$dir/../../build_tools/update_translations.fish --dry-run --use-existing-template=$FISH_GETTEXT_EXTRACTION_FILE
+or exit 1