Link to troubleshooting guide from exception messages

gson/src/main/java/com/google/gson/Gson.java

@@ -105,7 +105,7 @@
  * <p>See the <a href="https://github.com/google/gson/blob/master/UserGuide.md">Gson User Guide</a>
  * for a more complete set of examples.</p>
  *
- * <h2>Lenient JSON handling</h2>
+ * <h2 id="default-lenient">Lenient JSON handling</h2>
  * For legacy reasons most of the {@code Gson} methods allow JSON data which does not
  * comply with the JSON specification, regardless of whether {@link GsonBuilder#setLenient()}
  * is used or not. If this behavior is not desired, the following workarounds can be used:

gson/src/main/java/com/google/gson/internal/TroubleshootingGuide.java

@@ -0,0 +1,12 @@
+package com.google.gson.internal;
+
+public class TroubleshootingGuide {
+  private TroubleshootingGuide() {}
+
+  /**
+   * Creates a URL referring to the specified troubleshooting section.
+   */
+  public static String createUrl(String id) {
+    return "https://github.com/google/gson/blob/master/Troubleshooting.md#" + id;
+  }
+}

gson/src/main/java/com/google/gson/internal/bind/ReflectiveTypeAdapterFactory.java

@@ -33,6 +33,7 @@
 import com.google.gson.internal.ObjectConstructor;
 import com.google.gson.internal.Primitives;
 import com.google.gson.internal.ReflectionAccessFilterHelper;
+import com.google.gson.internal.TroubleshootingGuide;
 import com.google.gson.internal.reflect.ReflectionHelper;
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
@@ -114,7 +115,7 @@ public <T> TypeAdapter<T> create(Gson gson, final TypeToken<T> type) {
     if (filterResult == FilterResult.BLOCK_ALL) {
       throw new JsonIOException(
           "ReflectionAccessFilter does not permit using reflection for " + raw
-              + ". Register a TypeAdapter for this type or adjust the access filter.");
+          + ". Register a TypeAdapter for this type or adjust the access filter.");
     }
     boolean blockInaccessible = filterResult == FilterResult.BLOCK_INACCESSIBLE;
 
@@ -306,7 +307,8 @@ private Map<String, BoundField> getBoundFields(Gson context, TypeToken<?> type,
         if (previous != null) {
           throw new IllegalArgumentException("Class " + originalRaw.getName()
               + " declares multiple JSON fields named '" + previous.name + "'; conflict is caused"
-              + " by fields " + ReflectionHelper.fieldToString(previous.field) + " and " + ReflectionHelper.fieldToString(field));
+              + " by fields " + ReflectionHelper.fieldToString(previous.field) + " and " + ReflectionHelper.fieldToString(field)
+              + "\nSee " + TroubleshootingGuide.createUrl("duplicate-fields"));
         }
       }
       type = TypeToken.get($Gson$Types.resolve(type.getType(), raw, raw.getGenericSuperclass()));

gson/src/main/java/com/google/gson/internal/bind/TypeAdapters.java

@@ -28,6 +28,7 @@
 import com.google.gson.TypeAdapterFactory;
 import com.google.gson.annotations.SerializedName;
 import com.google.gson.internal.LazilyParsedNumber;
+import com.google.gson.internal.TroubleshootingGuide;
 import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
@@ -73,12 +74,14 @@ private TypeAdapters() {
     @Override
     public void write(JsonWriter out, Class value) throws IOException {
       throw new UnsupportedOperationException("Attempted to serialize java.lang.Class: "
-              + value.getName() + ". Forgot to register a type adapter?");
+          + value.getName() + ". Forgot to register a type adapter?"
+          + "\nSee " + TroubleshootingGuide.createUrl("java-lang-class-unsupported"));
     }
     @Override
     public Class read(JsonReader in) throws IOException {
       throw new UnsupportedOperationException(
-              "Attempted to deserialize a java.lang.Class. Forgot to register a type adapter?");
+          "Attempted to deserialize a java.lang.Class. Forgot to register a type adapter?"
+          + "\nSee " + TroubleshootingGuide.createUrl("java-lang-class-unsupported"));
     }
   }.nullSafe();
 

gson/src/main/java/com/google/gson/internal/reflect/ReflectionHelper.java

@@ -18,6 +18,7 @@
 
 import com.google.gson.JsonIOException;
 import com.google.gson.internal.GsonBuildConfig;
+import com.google.gson.internal.TroubleshootingGuide;
 import java.lang.reflect.AccessibleObject;
 import java.lang.reflect.Constructor;
 import java.lang.reflect.Field;
@@ -40,6 +41,17 @@ public class ReflectionHelper {
 
   private ReflectionHelper() {}
 
+  private static String getInaccessibleTroubleshootingSuffix(Exception e) {
+    // Class was added in Java 9, therefore cannot use instanceof
+    if (e.getClass().getName().equals("java.lang.reflect.InaccessibleObjectException")) {
+      String message = e.getMessage();
+      String troubleshootingId = message != null && message.contains("to module com.google.gson")
+          ? "reflection-inaccessible-to-module-gson" : "reflection-inaccessible";
+      return "\nSee " + TroubleshootingGuide.createUrl(troubleshootingId);
+    }
+    return "";
+  }
+
   /**
    * Internal implementation of making an {@link AccessibleObject} accessible.
    *
@@ -52,7 +64,8 @@ public static void makeAccessible(AccessibleObject object) throws JsonIOExceptio
     } catch (Exception exception) {
       String description = getAccessibleObjectDescription(object, false);
       throw new JsonIOException("Failed making " + description + " accessible; either increase its visibility"
-              + " or write a custom TypeAdapter for its declaring type.", exception);
+          + " or write a custom TypeAdapter for its declaring type." + getInaccessibleTroubleshootingSuffix(exception),
+          exception);
     }
   }
 
@@ -142,7 +155,7 @@ public static String tryMakeAccessible(Constructor<?> constructor) {
       return "Failed making constructor '" + constructorToString(constructor) + "' accessible;"
           + " either increase its visibility or write a custom InstanceCreator or TypeAdapter for"
           // Include the message since it might contain more detailed information
-          + " its declaring type: " + exception.getMessage();
+          + " its declaring type: " + exception.getMessage() + getInaccessibleTroubleshootingSuffix(exception);
     }
   }
 

gson/src/main/java/com/google/gson/stream/JsonReader.java

@@ -17,6 +17,7 @@
 package com.google.gson.stream;
 
 import com.google.gson.internal.JsonReaderInternalAccess;
+import com.google.gson.internal.TroubleshootingGuide;
 import com.google.gson.internal.bind.JsonTreeReader;
 import java.io.Closeable;
 import java.io.EOFException;
@@ -355,7 +356,7 @@ public void beginArray() throws IOException {
       pathIndices[stackSize - 1] = 0;
       peeked = PEEKED_NONE;
     } else {
-      throw new IllegalStateException("Expected BEGIN_ARRAY but was " + peek() + locationString());
+      throw unexpectedTokenError("BEGIN_ARRAY");
     }
   }
 
@@ -373,7 +374,7 @@ public void endArray() throws IOException {
       pathIndices[stackSize - 1]++;
       peeked = PEEKED_NONE;
     } else {
-      throw new IllegalStateException("Expected END_ARRAY but was " + peek() + locationString());
+      throw unexpectedTokenError("END_ARRAY");
     }
   }
 
@@ -390,7 +391,7 @@ public void beginObject() throws IOException {
       push(JsonScope.EMPTY_OBJECT);
       peeked = PEEKED_NONE;
     } else {
-      throw new IllegalStateException("Expected BEGIN_OBJECT but was " + peek() + locationString());
+      throw unexpectedTokenError("BEGIN_OBJECT");
     }
   }
 
@@ -409,7 +410,7 @@ public void endObject() throws IOException {
       pathIndices[stackSize - 1]++;
       peeked = PEEKED_NONE;
     } else {
-      throw new IllegalStateException("Expected END_OBJECT but was " + peek() + locationString());
+      throw unexpectedTokenError("END_OBJECT");
     }
   }
 
@@ -797,7 +798,7 @@ public String nextName() throws IOException {
     } else if (p == PEEKED_DOUBLE_QUOTED_NAME) {
       result = nextQuotedValue('"');
     } else {
-      throw new IllegalStateException("Expected a name but was " + peek() + locationString());
+      throw unexpectedTokenError("a name");
     }
     peeked = PEEKED_NONE;
     pathNames[stackSize - 1] = result;
@@ -833,7 +834,7 @@ public String nextString() throws IOException {
       result = new String(buffer, pos, peekedNumberLength);
       pos += peekedNumberLength;
     } else {
-      throw new IllegalStateException("Expected a string but was " + peek() + locationString());
+      throw unexpectedTokenError("a string");
     }
     peeked = PEEKED_NONE;
     pathIndices[stackSize - 1]++;
@@ -861,7 +862,7 @@ public boolean nextBoolean() throws IOException {
       pathIndices[stackSize - 1]++;
       return false;
     }
-    throw new IllegalStateException("Expected a boolean but was " + peek() + locationString());
+    throw unexpectedTokenError("a boolean");
   }
 
   /**
@@ -880,7 +881,7 @@ public void nextNull() throws IOException {
       peeked = PEEKED_NONE;
       pathIndices[stackSize - 1]++;
     } else {
-      throw new IllegalStateException("Expected null but was " + peek() + locationString());
+      throw unexpectedTokenError("null");
     }
   }
 
@@ -915,14 +916,13 @@ public double nextDouble() throws IOException {
     } else if (p == PEEKED_UNQUOTED) {
       peekedString = nextUnquotedValue();
     } else if (p != PEEKED_BUFFERED) {
-      throw new IllegalStateException("Expected a double but was " + peek() + locationString());
+      throw unexpectedTokenError("a double");
     }
 
     peeked = PEEKED_BUFFERED;
     double result = Double.parseDouble(peekedString); // don't catch this NumberFormatException.
     if (!lenient && (Double.isNaN(result) || Double.isInfinite(result))) {
-      throw new MalformedJsonException(
-          "JSON forbids NaN and infinities: " + result + locationString());
+      throw syntaxError("JSON forbids NaN and infinities: " + result);
     }
     peekedString = null;
     peeked = PEEKED_NONE;
@@ -970,7 +970,7 @@ public long nextLong() throws IOException {
         // Fall back to parse as a double below.
       }
     } else {
-      throw new IllegalStateException("Expected a long but was " + peek() + locationString());
+      throw unexpectedTokenError("a long");
     }
 
     peeked = PEEKED_BUFFERED;
@@ -1208,7 +1208,7 @@ public int nextInt() throws IOException {
         // Fall back to parse as a double below.
       }
     } else {
-      throw new IllegalStateException("Expected an int but was " + peek() + locationString());
+      throw unexpectedTokenError("an int");
     }
 
     peeked = PEEKED_BUFFERED;
@@ -1584,10 +1584,10 @@ public String getPath() {
   /**
    * Unescapes the character identified by the character or characters that
    * immediately follow a backslash. The backslash '\' should have already
-   * been read. This supports both unicode escapes "u000A" and two-character
+   * been read. This supports both Unicode escapes "u000A" and two-character
    * escapes "\n".
    *
-   * @throws MalformedJsonException if any unicode escape sequences are
+   * @throws MalformedJsonException if any Unicode escape sequences are
    *     malformed.
    */
   @SuppressWarnings("fallthrough")
@@ -1614,7 +1614,7 @@ private char readEscapeCharacter() throws IOException {
         } else if (c >= 'A' && c <= 'F') {
           result += (c - 'A' + 10);
         } else {
-          throw new MalformedJsonException("\\u" + new String(buffer, pos, 4));
+          throw syntaxError("Malformed Unicode escape \\u" + new String(buffer, pos, 4));
         }
       }
       pos += 4;
@@ -1656,7 +1656,16 @@ private char readEscapeCharacter() throws IOException {
    * with this reader's content.
    */
   private IOException syntaxError(String message) throws IOException {
-    throw new MalformedJsonException(message + locationString());
+    throw new MalformedJsonException(message + locationString()
+      + "\nSee " + TroubleshootingGuide.createUrl("malformed-json"));
+  }
+
+  private IllegalStateException unexpectedTokenError(String expected) throws IOException {
+    JsonToken peeked = peek();
+    String troubleshootingId = peeked == JsonToken.NULL
+        ? "adapter-not-null-safe" : "unexpected-json-structure";
+    return new IllegalStateException("Expected " + expected + " but was " + peek() + locationString()
+        + "\nSee " + TroubleshootingGuide.createUrl(troubleshootingId));
   }
 
   /**
@@ -1699,8 +1708,7 @@ private void consumeNonExecutePrefix() throws IOException {
         } else if (p == PEEKED_UNQUOTED_NAME) {
           reader.peeked = PEEKED_UNQUOTED;
         } else {
-          throw new IllegalStateException(
-              "Expected a name but was " + reader.peek() + reader.locationString());
+          throw reader.unexpectedTokenError("a name");
         }
       }
     };

gson/src/test/java/com/google/gson/JsonArrayTest.java

@@ -17,7 +17,6 @@
 package com.google.gson;
 
 import static com.google.common.truth.Truth.assertThat;
-import static com.google.common.truth.Truth.assertWithMessage;
 import static org.junit.Assert.fail;
 
 import com.google.common.testing.EqualsTester;
@@ -140,22 +139,19 @@ public void testFailedGetArrayValues() {
       jsonArray.getAsBoolean();
       fail("expected getBoolean to fail");
     } catch (UnsupportedOperationException e) {
-      assertWithMessage("Expected an exception message")
-          .that(e).hasMessageThat().isEqualTo("JsonObject");
+      assertThat(e).hasMessageThat().isEqualTo("JsonObject");
     }
     try {
       jsonArray.get(-1);
       fail("expected get to fail");
     } catch (IndexOutOfBoundsException e) {
-      assertWithMessage("Expected an exception message")
-          .that(e).hasMessageThat().isEqualTo("Index -1 out of bounds for length 1");
+      assertThat(e).hasMessageThat().isEqualTo("Index -1 out of bounds for length 1");
     }
     try {
       jsonArray.getAsString();
       fail("expected getString to fail");
     } catch (UnsupportedOperationException e) {
-      assertWithMessage("Expected an exception message")
-          .that(e).hasMessageThat().isEqualTo("JsonObject");
+      assertThat(e).hasMessageThat().isEqualTo("JsonObject");
     }
 
     jsonArray.remove(0);
@@ -164,36 +160,31 @@ public void testFailedGetArrayValues() {
       jsonArray.getAsDouble();
       fail("expected getDouble to fail");
     } catch (NumberFormatException e) {
-      assertWithMessage("Expected an exception message")
-          .that(e).hasMessageThat().isEqualTo("For input string: \"hello\"");
+      assertThat(e).hasMessageThat().isEqualTo("For input string: \"hello\"");
     }
     try {
       jsonArray.getAsInt();
       fail("expected getInt to fail");
     } catch (NumberFormatException e) {
-      assertWithMessage("Expected an exception message")
-          .that(e).hasMessageThat().isEqualTo("For input string: \"hello\"");
+      assertThat(e).hasMessageThat().isEqualTo("For input string: \"hello\"");
     }
     try {
       jsonArray.get(0).getAsJsonArray();
       fail("expected getJSONArray to fail");
     } catch (IllegalStateException e) {
-      assertWithMessage("Expected an exception message")
-          .that(e).hasMessageThat().isEqualTo("Not a JSON Array: \"hello\"");
+      assertThat(e).hasMessageThat().isEqualTo("Not a JSON Array: \"hello\"");
     }
     try {
       jsonArray.getAsJsonObject();
       fail("expected getJSONObject to fail");
     } catch (IllegalStateException e) {
-      assertWithMessage("Expected an exception message")
-          .that(e).hasMessageThat().isEqualTo( "Not a JSON Object: [\"hello\"]");
+      assertThat(e).hasMessageThat().isEqualTo("Not a JSON Object: [\"hello\"]");
     }
     try {
       jsonArray.getAsLong();
       fail("expected getLong to fail");
     } catch (NumberFormatException e) {
-      assertWithMessage("Expected an exception message")
-          .that(e).hasMessageThat().isEqualTo("For input string: \"hello\"");
+      assertThat(e).hasMessageThat().isEqualTo("For input string: \"hello\"");
     }
   }