Use getLast now that EP is on 21 (or will be after unknown commit)

RELNOTES=no
PiperOrigin-RevId: 826447287

Author: graememorgan

check_api/src/main/java/com/google/errorprone/apply/DescriptionBasedDiff.java

@@ -90,7 +90,7 @@ public boolean isEmpty() {
   public void onDescribed(Description description) {
     // Use only first (most likely) suggested fix
     if (description.fixes.size() > 0) {
-      handleFix(description.fixes.get(0));
+      handleFix(description.fixes.getFirst());
     }
   }
 

check_api/src/main/java/com/google/errorprone/dataflow/nullnesspropagation/NullnessPropagationTransfer.java

@@ -889,7 +889,7 @@ private static void setConditionalArgumentNullness(
       elseUpdates.set(var, NONNULL);
     }
     if (isEqualsMethod(calleeName, arguments, types, symtab)) {
-      LocalVariableNode var = variablesAtIndexes(ImmutableSet.of(0), arguments).get(0);
+      LocalVariableNode var = variablesAtIndexes(ImmutableSet.of(0), arguments).getFirst();
       thenUpdates.set(var, NONNULL);
     }
   }

check_api/src/main/java/com/google/errorprone/fixes/SuggestedFixes.java

@@ -582,7 +582,7 @@ int pos(ClassTree tree, VisitorState state) {
           // is just as good.
           return LAST.pos(tree, state);
         }
-        JCTree firstMember = (JCTree) members.get(0);
+        JCTree firstMember = (JCTree) members.getFirst();
         int firstMemberStart = firstMember.getStartPosition();
         List<ErrorProneToken> methodTokens = state.getOffsetTokens(classStart, firstMemberStart);
         ListIterator<ErrorProneToken> iter = methodTokens.listIterator(methodTokens.size());
@@ -744,7 +744,7 @@ public static SuggestedFix renameMethodInvocation(
     int endPos =
         tree.getArguments().isEmpty()
             ? state.getEndPosition(tree)
-            : getStartPosition(tree.getArguments().get(0));
+            : getStartPosition(tree.getArguments().getFirst());
     List<ErrorProneToken> tokens = state.getOffsetTokens(startPos, endPos);
     for (ErrorProneToken token : Lists.reverse(tokens)) {
       if (token.kind() == TokenKind.IDENTIFIER && token.name().equals(identifier)) {
@@ -909,7 +909,7 @@ public static Fix deleteExceptions(
             .map(state::getSourceForNode)
             .collect(joining(", "));
     return SuggestedFix.replace(
-        getStartPosition(tree.getThrows().get(0)),
+        getStartPosition(tree.getThrows().getFirst()),
         state.getEndPosition(getLast(tree.getThrows())),
         replacement);
   }
@@ -1135,7 +1135,7 @@ public static SuggestedFix.Builder addValuesToAnnotationArgument(
     if (!maybeExistingArgument.isPresent()) {
       return SuggestedFix.builder()
           .prefixWith(
-              annotation.getArguments().get(0),
+              annotation.getArguments().getFirst(),
               parameterName + " = " + newArgument(newValues) + ", ");
     }
 
@@ -1195,7 +1195,7 @@ public static SuggestedFix.Builder updateAnnotationArgumentValues(
     if (!maybeExistingArgument.isPresent()) {
       return SuggestedFix.builder()
           .prefixWith(
-              annotation.getArguments().get(0),
+              annotation.getArguments().getFirst(),
               parameterName + " = " + newArgument(newValues) + ", ");
     }
 
@@ -1667,19 +1667,19 @@ public static SuggestedFix replaceIncludingComments(
     //  int deletingThisVariable;
     // }
     // Treat this as morally part of the previous member.
-    if (!tokens.isEmpty() && tokens.get(0).kind() == TokenKind.SEMI) {
+    if (!tokens.isEmpty() && tokens.getFirst().kind() == TokenKind.SEMI) {
       tokens = tokens.subList(1, tokens.size());
     }
     if (tokens.isEmpty()) {
       return SuggestedFix.replace(tree, replacement);
     }
-    if (tokens.get(0).comments().isEmpty()) {
-      return SuggestedFix.replace(tokens.get(0).pos(), state.getEndPosition(tree), replacement);
+    if (tokens.getFirst().comments().isEmpty()) {
+      return SuggestedFix.replace(tokens.getFirst().pos(), state.getEndPosition(tree), replacement);
     }
     ImmutableList<ErrorProneComment> comments =
         ImmutableList.sortedCopyOf(
             Comparator.<ErrorProneComment>comparingInt(c -> c.getSourcePos(0)).reversed(),
-            tokens.get(0).comments());
+            tokens.getFirst().comments());
     int startPos = getStartPosition(tree);
     // This can happen for desugared expressions like `int a, b;`.
     if (startPos < startTokenization) {

check_api/src/main/java/com/google/errorprone/matchers/JUnitMatchers.java

@@ -17,6 +17,7 @@
 package com.google.errorprone.matchers;
 
 import static com.google.common.base.MoreObjects.firstNonNull;
+import static com.google.common.collect.Iterables.getOnlyElement;
 import static com.google.errorprone.matchers.ChildMultiMatcher.MatchType.AT_LEAST_ONE;
 import static com.google.errorprone.matchers.Matchers.allOf;
 import static com.google.errorprone.matchers.Matchers.annotations;
@@ -236,7 +237,7 @@ public boolean matches(ExpressionTree t, VisitorState state) {
         if (typeArgs.size() != 1) {
           return false;
         }
-        Type runnerType = typeArgs.get(0);
+        Type runnerType = getOnlyElement(typeArgs);
         for (String testRunner : runnerTypes) {
           Symbol parent = state.getSymbolFromString(testRunner);
           if (parent == null) {

check_api/src/main/java/com/google/errorprone/matchers/UnusedReturnValueMatcher.java

@@ -16,6 +16,7 @@
 
 package com.google.errorprone.matchers;
 
+import static com.google.common.collect.Iterables.getOnlyElement;
 import static com.google.errorprone.matchers.Matchers.allOf;
 import static com.google.errorprone.matchers.Matchers.anyOf;
 import static com.google.errorprone.matchers.Matchers.enclosingMethod;
@@ -228,7 +229,7 @@ private static boolean isOnlyStatementInBlock(StatementTree t, VisitorState s) {
     BlockTree parentBlock = ASTHelpers.findEnclosingNode(s.getPath(), BlockTree.class);
     return parentBlock != null
         && parentBlock.getStatements().size() == 1
-        && parentBlock.getStatements().get(0) == t;
+        && getOnlyElement(parentBlock.getStatements()) == t;
   }
 
   /** Allow return values to be ignored in tests that expect an exception to be thrown. */

check_api/src/main/java/com/google/errorprone/util/MoreAnnotations.java

@@ -66,7 +66,7 @@ public static Stream<Compound> getDeclarationAndTypeAttributes(Symbol sym) {
             groupingBy(c -> c.type.asElement().getQualifiedName(), LinkedHashMap::new, toList()))
         .values()
         .stream()
-        .map(c -> c.get(0));
+        .map(c -> c.getFirst());
   }
 
   /**

core/src/main/java/com/google/errorprone/bugpatterns/AbstractAsKeyOfSetOrMap.java

@@ -98,7 +98,7 @@ private Description matchType(ExpressionTree tree, VisitorState state) {
       if (argumentTypes.isEmpty()) {
         return Description.NO_MATCH;
       }
-      Type typeArg = argumentTypes.get(0);
+      Type typeArg = argumentTypes.getFirst();
       if (isBadType(typeArg, state)) {
         return describeMatch(tree);
       }

core/src/main/java/com/google/errorprone/bugpatterns/AbstractMockChecker.java

@@ -173,7 +173,7 @@ public static TypeExtractor<MethodInvocationTree> extractFirstArg(
         return Optional.empty();
       }
       if (tree.getArguments().size() >= 1) {
-        return Optional.ofNullable(ASTHelpers.getType(tree.getArguments().get(0)));
+        return Optional.ofNullable(ASTHelpers.getType(tree.getArguments().getFirst()));
       }
       return Optional.ofNullable(TargetType.targetType(state)).map(t -> t.type());
     };

core/src/main/java/com/google/errorprone/bugpatterns/AbstractMustBeClosedChecker.java

@@ -529,7 +529,8 @@ private static Optional<Change> wrapTryFinallyAroundVariableScope(
    */
   private static boolean isClosingDecorator(
       NewClassTree decorator, Tree resource, VisitorState state) {
-    if (decorator.getArguments().isEmpty() || !decorator.getArguments().get(0).equals(resource)) {
+    if (decorator.getArguments().isEmpty()
+        || !decorator.getArguments().getFirst().equals(resource)) {
       // we assume the decorated resource is always the first argument to the decorator constructor
       return false;
     }
@@ -538,7 +539,7 @@ private static boolean isClosingDecorator(
       // resource would not be closed if the decorator constructor throws
       return false;
     }
-    Type resourceType = constructor.params().get(0).type;
+    Type resourceType = constructor.params().getFirst().type;
     Type decoratorType = constructor.owner.type;
     return CLOSEABLE_DECORATOR_TYPES.keySet().stream()
         .filter(key -> isSameType(resourceType, state.getTypeFromString(key), state))

core/src/main/java/com/google/errorprone/bugpatterns/AbstractReturnValueIgnored.java

@@ -264,7 +264,7 @@ final ImmutableList<Fix> fixesAtCallSite(ExpressionTree invocationTree, VisitorS
     ImmutableMap.Builder<String, SuggestedFix> fixes = ImmutableMap.builder();
     if (MOCKITO_VERIFY.matches(invocationTree, state)) {
       ExpressionTree maybeCallToMock =
-          ((MethodInvocationTree) invocationTree).getArguments().get(0);
+          ((MethodInvocationTree) invocationTree).getArguments().getFirst();
       if (maybeCallToMock instanceof MethodInvocationTree methodInvocationTree) {
         ExpressionTree maybeMethodSelectOnMock = methodInvocationTree.getMethodSelect();
         if (maybeMethodSelectOnMock instanceof MemberSelectTree maybeSelectOnMock) {
@@ -420,7 +420,7 @@ private Description checkLostType(MethodInvocationTree tree, VisitorState state)
         && !returnedFutureType.hasTag(TypeTag.ERROR) // work around error-prone#996
         && !returnedFutureType.isRaw()) {
       if (isSubtype(
-          getUpperBound(returnedFutureType.getTypeArguments().get(0), state.getTypes()),
+          getUpperBound(returnedFutureType.getTypeArguments().getFirst(), state.getTypes()),
           lostType,
           state)) {
         return buildDescription(tree)