add /target/ to .gitignore files for all crates (#4217)

* add /target/ to .gitignore files for all crates

* shellcheck

ci/nits.sh

@@ -38,3 +38,17 @@ if _ git grep 'Default::default()' -- '*.rs'; then
     exit 1
 fi
 
+# Let's keep a .gitignore for every crate, ensure it's got
+#  /target/ in it
+declare gitignores_ok=true
+for i in $(git ls-files \*/Cargo.toml ); do
+  dir=$(dirname "$i")
+  if [[ ! -f $dir/.gitignore ]]; then
+      echo 'error: nits.sh .gitnore missing for crate '"$dir" >&2
+      gitignores_ok=false
+  elif ! grep -q -e '^/target/$' "$dir"/.gitignore; then
+      echo 'error: nits.sh "/target/" apparently missing from '"$dir"'/.gitignore' >&2
+      gitignores_ok=false
+  fi
+done
+"$gitignores_ok"