Style guide allows empty catch blocks with clear parameter names sett…

…ing up expectation.

Exempting expected, ignored and ok parameter names.

https://google.github.io/styleguide/javaguide.html#s6.2-caught-exceptions

Inverse flume results (matches that won't be flagged now) : unknown commit

Fixes #1654

PiperOrigin-RevId: 322052035

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

@@ -20,13 +20,15 @@
 import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
 import static com.google.errorprone.matchers.Description.NO_MATCH;
 
+import com.google.common.collect.ImmutableSet;
 import com.google.errorprone.BugPattern;
 import com.google.errorprone.VisitorState;
 import com.google.errorprone.bugpatterns.BugChecker.CatchTreeMatcher;
 import com.google.errorprone.matchers.Description;
 import com.google.errorprone.util.ASTHelpers;
 import com.sun.source.tree.BlockTree;
 import com.sun.source.tree.CatchTree;
+import com.sun.source.tree.VariableTree;
 
 /** A {@link BugChecker}; see the associated {@link BugPattern} annotation for details. */
 @BugPattern(
@@ -39,6 +41,9 @@
     )
 public class EmptyCatch extends BugChecker implements CatchTreeMatcher {
 
+  private static final ImmutableSet<String> EXEMPTED_PARAMETER_NAMES =
+      ImmutableSet.of("expected", "ok", "ignored");
+
   @Override
   public Description matchCatch(CatchTree tree, VisitorState state) {
     BlockTree block = tree.getBlock();
@@ -51,6 +56,11 @@ public Description matchCatch(CatchTree tree, VisitorState state) {
     if (ASTHelpers.isJUnitTestCode(state)) {
       return NO_MATCH;
     }
+    VariableTree param = tree.getParameter();
+    if (EXEMPTED_PARAMETER_NAMES.stream()
+        .anyMatch(paramName -> param.getName().contentEquals(paramName))) {
+      return NO_MATCH;
+    }
     return describeMatch(tree);
   }
 }

core/src/test/java/com/google/errorprone/bugpatterns/testdata/EmptyCatchNegativeCases.java

@@ -126,11 +126,32 @@ public void catchIsLoggedOnly() {
   }
 
   @Test
-  public void expectedException() {
+  public void expectedExceptionInTest() {
     try {
       System.err.println();
       fail();
     } catch (Exception expected) {
     }
   }
+
+  public void expectedException() {
+    try {
+      System.err.println();
+    } catch (Exception expected) {
+    }
+  }
+
+  public void ignoredException() {
+    try {
+      System.err.println();
+    } catch (Exception ignored) {
+    }
+  }
+
+  public void okException() {
+    try {
+      System.err.println();
+    } catch (Exception ok) {
+    }
+  }
 }