Add lint to ensure substitutions use the full form

Check that any variable substitutions use the full ${VAR} form,
not just $VAR (but don't check for quoting yet).

components/servo/fake-ld.sh

@@ -9,7 +9,7 @@ set -o nounset
 set -o pipefail
 
 TARGET_DIR="${OUT_DIR}/../../.."
-arm-linux-androideabi-gcc "$@" \
+arm-linux-androideabi-gcc "${@}" \
                           "${LDFLAGS-}" -lc -shared \
                           -o "${TARGET_DIR}/libservo.so"
 touch "${TARGET_DIR}/servo"

etc/ci/lockfile_changed.sh

@@ -9,5 +9,5 @@ set -o nounset
 set -o pipefail
 
 diff="$(git diff -- */*/Cargo.lock)"
-echo "$diff"
-[[ ! $diff ]]
+echo "${diff}"
+[[ -z "${diff}" ]]

etc/ci/manifest_changed.sh

@@ -17,5 +17,5 @@ set -o pipefail
 ./mach test-wpt --manifest-update --binary= SKIP_TESTS > /dev/null
 
 diff="$(git diff -- tests/*/MANIFEST.json)"
-echo "$diff"
-[[ ! $diff ]]
+echo "${diff}"
+[[ -z "${diff}" ]]

etc/ci/upload_docs.sh

@@ -12,7 +12,7 @@ set -o errexit
 set -o nounset
 set -o pipefail
 
-cd "$(dirname $0)/../.."
+cd "$(dirname ${0})/../.."
 
 ./mach doc
 # etc/doc.servo.org/index.html overwrites $(mach rust-root)/doc/index.html

etc/ci/upload_nightly.sh

@@ -27,7 +27,7 @@ upload() {
 
 
 main() {
-    if [[ "$#" != 1 ]]; then
+    if [[ "${#}" != 1 ]]; then
         usage >&2
         return 1
     fi
@@ -58,4 +58,4 @@ main() {
     upload "${platform}" ${package} "${extension}"
 }
 
-main "$@"
+main "${@}"

ports/geckolib/gecko_bindings/tools/regen.sh

@@ -8,8 +8,8 @@ set -o errexit
 set -o nounset
 set -o pipefail
 
-if [ $# -eq 0 ]; then
-  echo "Usage: $0 /path/to/gecko/objdir [other-regen.py-flags]"
+if [ ${#} -eq 0 ]; then
+  echo "Usage: ${0} /path/to/gecko/objdir [other-regen.py-flags]"
   exit 1
 fi
 
@@ -32,4 +32,4 @@ else
   LIBCLANG_PATH="$(brew --prefix llvm38)/lib/llvm-3.8/lib"
 fi
 
-./regen.py --target all "$@"
+./regen.py --target all "${@}"

ports/geckolib/gecko_bindings/tools/setup_bindgen.sh

@@ -9,7 +9,7 @@ set -o nounset
 set -o pipefail
 
 # Run in the tools directory.
-cd "$(dirname $0)"
+cd "$(dirname ${0})"
 
 # Setup and build bindgen.
 if [ "$(uname)" == "Linux" ]; then
@@ -25,8 +25,8 @@ if [ ! -x "$(command -v clang-3.8)" ]; then
     exit 1
 fi
 
-export LD_LIBRARY_PATH=$LIBCLANG_PATH
-export DYLD_LIBRARY_PATH=$LIBCLANG_PATH
+export LD_LIBRARY_PATH="${LIBCLANG_PATH}"
+export DYLD_LIBRARY_PATH="${LIBCLANG_PATH}"
 
 # Check for multirust
 if [ ! -x "$(command -v multirust)" ]; then

python/tidy/servo_tidy/tidy.py

@@ -347,6 +347,13 @@ def check_shell(file_name, lines):
         if "`" in stripped:
             yield (idx + 1, "script should not use backticks for command substitution")
 
+        for dollar in re.finditer('\$', stripped):
+            next_idx = dollar.end()
+            if next_idx < len(stripped):
+                next_char = stripped[next_idx]
+                if not (next_char == '{' or next_char == '('):
+                    yield(idx + 1, "variable substitutions should use the full \"${VAR}\" form")
+
 
 def check_rust(file_name, lines):
     if not file_name.endswith(".rs") or \

python/tidy/servo_tidy_tests/shell_tidy.sh

@@ -7,3 +7,4 @@ set -o nounset
 # Talking about some `concept in backticks` # shouldn't trigger
 echo "hello world"
 some_var=`echo "command substitution"`
+another_var="$some_var"

python/tidy/servo_tidy_tests/test_tidy.py

@@ -53,6 +53,7 @@ class CheckTidiness(unittest.TestCase):
         self.assertEqual('script does not have shebang "#!/usr/bin/env bash"', errors.next()[2])
         self.assertEqual('script is missing options "set -o errexit", "set -o pipefail"', errors.next()[2])
         self.assertEqual('script should not use backticks for command substitution', errors.next()[2])
+        self.assertEqual('variable substitutions should use the full \"${VAR}\" form', errors.next()[2])
         self.assertNoMoreErrors(errors)
 
     def test_rust(self):