UnusedVariable: subject the parameters of @Inject &c methods to analy…

…sis.

These should be used, or they should be removed. Removing them should be safe, given only the framework should be calling them.

I used "should" a lot there; they could be manually invoked, but that's a problem unto itself.

PiperOrigin-RevId: 499443898

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

@@ -28,6 +28,7 @@
 import static com.google.errorprone.util.ASTHelpers.getStartPosition;
 import static com.google.errorprone.util.ASTHelpers.getSymbol;
 import static com.google.errorprone.util.ASTHelpers.getType;
+import static com.google.errorprone.util.ASTHelpers.hasAnnotation;
 import static com.google.errorprone.util.ASTHelpers.isStatic;
 import static com.google.errorprone.util.ASTHelpers.isSubtype;
 import static com.google.errorprone.util.ASTHelpers.shouldKeep;
@@ -141,6 +142,16 @@ public final class UnusedVariable extends BugChecker implements CompilationUnitT
           "org.apache.beam.sdk.transforms.DoFn.TimerId",
           "org.apache.beam.sdk.transforms.DoFn.StateId");
 
+  // TODO(ghm): Find a sensible place to dedupe this with UnnecessarilyVisible.
+  private static final ImmutableSet<String> ANNOTATIONS_INDICATING_PARAMETERS_SHOULD_BE_CHECKED =
+      ImmutableSet.of(
+          "com.google.inject.Inject",
+          "com.google.inject.Provides",
+          "com.google.inject.multibindings.ProvidesIntoMap",
+          "com.google.inject.multibindings.ProvidesIntoSet",
+          "dagger.Provides",
+          "javax.inject.Inject");
+
   private final ImmutableSet<String> methodAnnotationsExemptingParameters;
 
   /** The set of types exempting a type that is extending or implementing them. */
@@ -640,11 +651,16 @@ private boolean isParameterSubjectToAnalysis(Symbol sym) {
       Symbol enclosingMethod = sym.owner;
 
       for (String annotationName : methodAnnotationsExemptingParameters) {
-        if (ASTHelpers.hasAnnotation(enclosingMethod, annotationName, state)) {
+        if (hasAnnotation(enclosingMethod, annotationName, state)) {
           return false;
         }
       }
 
+      if (ANNOTATIONS_INDICATING_PARAMETERS_SHOULD_BE_CHECKED.stream()
+          .anyMatch(a -> hasAnnotation(enclosingMethod, a, state))) {
+        return true;
+      }
+
       return enclosingMethod.getModifiers().contains(Modifier.PRIVATE);
     }
 

core/src/test/java/com/google/errorprone/bugpatterns/UnusedVariableTest.java

@@ -708,6 +708,21 @@ public void unusedInject() {
         .doTest();
   }
 
+  @Test
+  public void unusedInjectConstructorParameter() {
+    helper
+        .addSourceLines(
+            "Test.java",
+            "package unusedvars;",
+            "import javax.inject.Inject;",
+            "public class Test {",
+            "  @Inject Test(",
+            "    // BUG: Diagnostic contains:",
+            "    String foo) {}",
+            "}")
+        .doTest();
+  }
+
   @Test
   public void unusedInject_notByDefault() {
     helper