SONARJAVA-5015 Improve the tolerance to syntax errors when parsing switch expressions (#4926)

Author: alban-auzeill

java-frontend/src/main/java/org/sonar/java/model/JParser.java

@@ -258,7 +258,19 @@ public class JParser {
 
   private static final Logger LOG = LoggerFactory.getLogger(JParser.class);
 
-  private static final Predicate<IProblem> IS_SYNTAX_ERROR = error -> (error.getID() & IProblem.Syntax) != 0;
+  private static final Set<Integer> WRONGLY_CATEGORIZED_AS_SYNTAX_ERROR = Set.of(
+    // Accept missing default clause, it may be due to missing semantic information of the switch expression,
+    // in this case, an enum fully covered with the switch cases will be seen as something that is not an enum
+    // when it is unknown, and the parser will wrongly consider the missing default clause as a syntax error.
+    IProblem.SwitchExpressionsYieldMissingDefaultCase,
+    // Accept missing default clause, it may be due the switch expression being an enum from a wrong dependency.
+    // In this case, the parser will wrongly consider the missing default clause as a syntax error.
+    IProblem.SwitchExpressionsYieldMissingEnumConstantCase
+  );
+
+  private static final Predicate<IProblem> IS_SYNTAX_ERROR = error -> ((error.getID() & IProblem.Syntax) != 0) &&
+    !WRONGLY_CATEGORIZED_AS_SYNTAX_ERROR.contains(error.getID());
+
   private static final Predicate<IProblem> IS_UNDEFINED_TYPE_ERROR = error -> (error.getID() & IProblem.UndefinedType) != 0;
 
   /**

java-frontend/src/test/java/org/sonar/java/model/JParserSemanticTest.java

@@ -88,6 +88,7 @@
 import org.sonar.plugins.java.api.tree.TypeCastTree;
 import org.sonar.plugins.java.api.tree.TypeTree;
 import org.sonar.plugins.java.api.tree.VariableTree;
+import org.sonar.plugins.java.api.tree.YieldStatementTree;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
@@ -559,6 +560,36 @@ void expression_switch() {
     }
   }
 
+  @Test
+  void switch_expression_with_yield_of_unknown_identifier_without_default_clause() {
+    SwitchExpressionTreeImpl switchExpression = (SwitchExpressionTreeImpl) expression("switch (unknownIdentifier) { case A -> 0; case B -> 1; }");
+    assertThat(switchExpression.expression().symbolType().isUnknown()).isTrue();
+    // the expression type of the full switch expression the should have been int or unknown
+    // instead of java.lang.Object, it is probably a limitation in the JDT parser when it face a missing default clause error
+    assertThat(switchExpression.symbolType().isUnknown()).isFalse();
+    assertThat(switchExpression.symbolType().fullyQualifiedName()).isEqualTo("java.lang.Object");
+    assertThat(switchExpression.cases().get(0).body().get(0)).isInstanceOf(YieldStatementTree.class);
+  }
+
+  @Test
+  void switch_expression_of_unknown_identifier_without_default_clause() {
+    SwitchExpressionTreeImpl switchExpression = (SwitchExpressionTreeImpl) expression("switch (unknownIdentifier) { case A: return 0; case B: return 1; }");
+    assertThat(switchExpression.expression().symbolType().isUnknown()).isTrue();
+    assertThat(switchExpression.symbolType().isUnknown()).isTrue();
+    assertThat(switchExpression.cases().get(0).body().get(0)).isInstanceOf(ReturnStatementTree.class);
+  }
+
+  @Test
+  void switch_expression_of_enum_without_default_clause() {
+    CompilationUnitTree cu = test("class C { Object m(java.time.DayOfWeek x) { return switch (x) { case MONDAY: return 0; case TUESDAY: return 1; } ; } }");
+    ClassTree c = (ClassTree) cu.types().get(0);
+    MethodTree m = (MethodTree) c.members().get(0);
+    ReturnStatementTree s = (ReturnStatementTree) Objects.requireNonNull(m.block()).body().get(0);
+    SwitchExpressionTreeImpl switchExpression = (SwitchExpressionTreeImpl) s.expression();
+    assertThat(switchExpression.expression().symbolType().isUnknown()).isFalse();
+    assertThat(switchExpression.symbolType().isUnknown()).isTrue();
+  }
+
   /**
    * Pattern Matching for instanceof
    * (Preview in Java 14) https://openjdk.java.net/jeps/305