Remove unused annotation imports in Checker stubs (#1510)

config/checker/com.intellij.astub

@@ -1,6 +1,5 @@
 
 import org.checkerframework.checker.guieffect.qual.AlwaysSafe;
-import org.checkerframework.checker.guieffect.qual.PolyUI;
 import org.checkerframework.checker.guieffect.qual.PolyUIEffect;
 import org.checkerframework.checker.guieffect.qual.PolyUIType;
 import org.checkerframework.checker.guieffect.qual.SafeEffect;

scripts/enforce-astub-explicit-annotation-import

@@ -8,16 +8,20 @@ source "$self_dir"/utils.sh
 exit_code=0
 
 for file in $(git ls-files '*.astub'); do
-  # Print the lines present in the first output but missing from the second
-  # First <(...) covers all annotations used across the file,
-  # second <(...) covers all symbols imported in the file.
-  output=$(comm -23 \
-    <(grep -Po '(?<=@)[a-zA-Z0-9.]*' "$file" | sort -u) \
-    <(grep -Po '(?<=import ).*(?=;)' "$file" | rev | cut -d. -f1 | rev | sort -u)
-  )
+  annotations_imported_in_file=$(grep -Po '(?<=import ).*(?=;)' "$file" | rev | cut -d. -f1 | rev | sort -u)
+  annotations_used_across_file=$(grep -Po '(?<=@)[a-zA-Z0-9.]*' "$file" | sort -u)
 
-  if [[ $output ]]; then
-    echo "$file: $(echo -n "$output" | tr '\n' ',' | sed 's/,/, /g') must be imported explicitly"
+  # Print the lines missing from the first input but present in the second
+  unimported_annotations=$(comm -13 <(echo "$annotations_imported_in_file") <(echo "$annotations_used_across_file"))
+  if [[ $unimported_annotations ]]; then
+    echo "$file: $(echo -n "$unimported_annotations" | tr '\n' ',' | sed 's/,/, /g') must be imported explicitly"
+    exit_code=1
+  fi
+
+  # Print the lines present in the first input but missing from the second
+  unused_annotations=$(comm -23 <(echo "$annotations_imported_in_file") <(echo "$annotations_used_across_file"))
+  if [[ $unused_annotations ]]; then
+    echo "$file: $(echo -n "$unused_annotations" | tr '\n' ',' | sed 's/,/, /g') imported but unused"
     exit_code=1
   fi
 done