From 1ae734ce1b656c32d6cd80f27cc595f690396e35 Mon Sep 17 00:00:00 2001
From: bhagwani <bhagwani@google.com>
Date: Sun, 19 Jul 2020 15:25:23 -0700
Subject: [PATCH] Style guide allows empty catch blocks with clear parameter
 names setting 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
---
 .../errorprone/bugpatterns/EmptyCatch.java    | 10 ++++++++
 .../testdata/EmptyCatchNegativeCases.java     | 23 ++++++++++++++++++-
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/EmptyCatch.java b/core/src/main/java/com/google/errorprone/bugpatterns/EmptyCatch.java
index 8b6020a70d5..fd2e36751a7 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/EmptyCatch.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/EmptyCatch.java
@@ -20,6 +20,7 @@
 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;
@@ -27,6 +28,7 @@
 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);
   }
 }
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/testdata/EmptyCatchNegativeCases.java b/core/src/test/java/com/google/errorprone/bugpatterns/testdata/EmptyCatchNegativeCases.java
index 57d7f72a656..4fa5ac8e1ae 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/testdata/EmptyCatchNegativeCases.java
+++ b/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) {
+    }
+  }
 }