feat(ast): Add support for Throwable causes [ggj]

src/main/java/com/google/api/generator/engine/ast/ThrowExpr.java

@@ -28,6 +28,9 @@ public abstract class ThrowExpr implements Expr {
   @Nullable
   public abstract Expr messageExpr();
 
+  @Nullable
+  public abstract Expr causeExpr();
+
   @Override
   public void accept(AstNodeVisitor visitor) {
     visitor.visit(this);
@@ -47,22 +50,36 @@ public Builder setMessageExpr(String message) {
 
     public abstract Builder setMessageExpr(Expr expr);
 
+    public abstract Builder setCauseExpr(Expr expr);
+
     // Private.
     abstract TypeNode type();
 
     abstract Expr messageExpr();
 
+    abstract Expr causeExpr();
+
     abstract ThrowExpr autoBuild();
 
     public ThrowExpr build() {
       Preconditions.checkState(
           TypeNode.isExceptionType(type()),
           String.format("Type %s must be an exception type", type()));
+
       if (messageExpr() != null) {
         Preconditions.checkState(
             messageExpr().type().equals(TypeNode.STRING),
             String.format("Message expression type must be a string for exception %s", type()));
       }
+
+      if (causeExpr() != null) {
+        Preconditions.checkState(
+            TypeNode.THROWABLE.reference().isSupertypeOrEquals(causeExpr().type().reference()),
+            String.format(
+                "Cause expression type must be a subclass of Throwable, but found %s",
+                causeExpr().type()));
+      }
+
       return autoBuild();
     }
   }

src/main/java/com/google/api/generator/engine/ast/TypeNode.java

@@ -81,6 +81,9 @@ public enum TypeKind {
   public static final TypeNode STRING = withReference(ConcreteReference.withClazz(String.class));
   public static final TypeNode VOID_OBJECT = withReference(ConcreteReference.withClazz(Void.class));
 
+  public static final TypeNode THROWABLE =
+      withReference(ConcreteReference.withClazz(Throwable.class));
+
   public static final TypeNode DEPRECATED =
       withReference(ConcreteReference.withClazz(Deprecated.class));
 

src/main/java/com/google/api/generator/engine/writer/ImportWriterVisitor.java

@@ -234,6 +234,9 @@ public void visit(ThrowExpr throwExpr) {
     if (throwExpr.messageExpr() != null) {
       throwExpr.messageExpr().accept(this);
     }
+    if (throwExpr.causeExpr() != null) {
+      throwExpr.causeExpr().accept(this);
+    }
   }
 
   @Override

src/main/java/com/google/api/generator/engine/writer/JavaWriterVisitor.java

@@ -399,6 +399,13 @@ public void visit(ThrowExpr throwExpr) {
     if (throwExpr.messageExpr() != null) {
       throwExpr.messageExpr().accept(this);
     }
+    if (throwExpr.causeExpr() != null) {
+      if (throwExpr.messageExpr() != null) {
+        buffer.append(COMMA);
+        space();
+      }
+      throwExpr.causeExpr().accept(this);
+    }
     rightParen();
   }
 

src/test/java/com/google/api/generator/engine/ast/ThrowExprTest.java

@@ -62,4 +62,65 @@ public void createThrowExpr_badMessageExpr() {
         IllegalStateException.class,
         () -> ThrowExpr.builder().setType(npeType).setMessageExpr(messageExpr).build());
   }
+
+  @Test
+  public void createThrowExpr_causeExpr() {
+    TypeNode npeType =
+        TypeNode.withReference(ConcreteReference.withClazz(NullPointerException.class));
+    ThrowExpr.builder()
+        .setType(npeType)
+        .setCauseExpr(
+            NewObjectExpr.builder()
+                .setType(TypeNode.withReference(ConcreteReference.withClazz(Throwable.class)))
+                .build())
+        .build();
+    // Successfully created a ThrowExpr.
+  }
+
+  @Test
+  public void createThrowExpr_causeExpr_throwableSubtype() {
+    TypeNode npeType =
+        TypeNode.withReference(ConcreteReference.withClazz(NullPointerException.class));
+    ThrowExpr.builder()
+        .setType(npeType)
+        .setCauseExpr(
+            NewObjectExpr.builder()
+                .setType(TypeNode.withExceptionClazz(IllegalStateException.class))
+                .build())
+        .build();
+    // Successfully created a ThrowExpr.
+  }
+
+  @Test
+  public void createThrowExpr_causeExpr_onThrowableSubtype() {
+    TypeNode npeType =
+        TypeNode.withReference(ConcreteReference.withClazz(NullPointerException.class));
+    assertThrows(
+        IllegalStateException.class,
+        () ->
+            ThrowExpr.builder()
+                .setType(npeType)
+                .setCauseExpr(NewObjectExpr.builder().setType(TypeNode.STRING).build())
+                .build());
+  }
+
+  @Test
+  public void createThrowExpr_messageAndCauseExpr() {
+    TypeNode npeType =
+        TypeNode.withReference(ConcreteReference.withClazz(NullPointerException.class));
+    Expr messageExpr =
+        MethodInvocationExpr.builder()
+            .setMethodName("foobar")
+            .setReturnType(TypeNode.STRING)
+            .build();
+    ThrowExpr.builder()
+        .setType(npeType)
+        .setMessageExpr(messageExpr)
+        .setCauseExpr(
+            NewObjectExpr.builder()
+                .setType(TypeNode.withReference(ConcreteReference.withClazz(Throwable.class)))
+                .build())
+        .build();
+    // Successfully created a ThrowExpr.
+  }
 }

src/test/java/com/google/api/generator/engine/writer/ImportWriterVisitorTest.java

@@ -58,6 +58,7 @@
 import com.google.common.base.Function;
 import com.google.common.base.Strings;
 import java.io.File;
+import java.io.FileNotFoundException;
 import java.io.FileOutputStream;
 import java.io.IOException;
 import java.util.ArrayList;
@@ -475,6 +476,42 @@ public void writeThrowExprImports_messageExpr() {
         writerVisitor.write());
   }
 
+  @Test
+  public void writeThrowExprImports_messageAndCauseExpr() {
+    TypeNode npeType = TypeNode.withExceptionClazz(NullPointerException.class);
+    Expr messageExpr =
+        MethodInvocationExpr.builder()
+            .setStaticReferenceType(
+                TypeNode.withReference(ConcreteReference.withClazz(IfStatement.class)))
+            .setMethodName("conditionExpr")
+            .setReturnType(TypeNode.withReference(ConcreteReference.withClazz(Expr.class)))
+            .build();
+
+    messageExpr =
+        MethodInvocationExpr.builder()
+            .setExprReferenceExpr(messageExpr)
+            .setMethodName("foobar")
+            .setReturnType(TypeNode.STRING)
+            .build();
+    ThrowExpr throwExpr =
+        ThrowExpr.builder()
+            .setType(npeType)
+            .setMessageExpr(messageExpr)
+            .setCauseExpr(
+                NewObjectExpr.builder()
+                    .setType(TypeNode.withExceptionClazz(FileNotFoundException.class))
+                    .build())
+            .build();
+
+    throwExpr.accept(writerVisitor);
+    assertEquals(
+        LineFormatter.lines(
+            "import com.google.api.generator.engine.ast.Expr;\n",
+            "import com.google.api.generator.engine.ast.IfStatement;\n",
+            "import java.io.FileNotFoundException;\n\n"),
+        writerVisitor.write());
+  }
+
   @Test
   public void writeInstanceofExprImports_basic() {
     TypeNode exprType = TypeNode.withReference(ConcreteReference.withClazz(Expr.class));

src/test/java/com/google/api/generator/engine/writer/JavaWriterVisitorTest.java

@@ -1041,6 +1041,22 @@ public void writeThrowExpr_basicWithMessage() {
     assertEquals("throw new NullPointerException(\"Some message asdf\")", writerVisitor.write());
   }
 
+  @Test
+  public void writeThrowExpr_basicWithCause() {
+    TypeNode npeType =
+        TypeNode.withReference(ConcreteReference.withClazz(NullPointerException.class));
+    ThrowExpr throwExpr =
+        ThrowExpr.builder()
+            .setType(npeType)
+            .setCauseExpr(
+                NewObjectExpr.builder()
+                    .setType(TypeNode.withReference(ConcreteReference.withClazz(Throwable.class)))
+                    .build())
+            .build();
+    throwExpr.accept(writerVisitor);
+    assertEquals("throw new NullPointerException(new Throwable())", writerVisitor.write());
+  }
+
   @Test
   public void writeThrowExpr_messageExpr() {
     TypeNode npeType = TypeNode.withExceptionClazz(NullPointerException.class);
@@ -1055,6 +1071,29 @@ public void writeThrowExpr_messageExpr() {
     assertEquals("throw new NullPointerException(foobar())", writerVisitor.write());
   }
 
+  @Test
+  public void writeThrowExpr_messageAndCauseExpr() {
+    TypeNode npeType = TypeNode.withExceptionClazz(NullPointerException.class);
+    Expr messageExpr =
+        MethodInvocationExpr.builder()
+            .setMethodName("foobar")
+            .setReturnType(TypeNode.STRING)
+            .build();
+    ThrowExpr throwExpr =
+        ThrowExpr.builder()
+            .setType(npeType)
+            .setMessageExpr(messageExpr)
+            .setCauseExpr(
+                NewObjectExpr.builder()
+                    .setType(TypeNode.withReference(ConcreteReference.withClazz(Throwable.class)))
+                    .build())
+            .build();
+
+    throwExpr.accept(writerVisitor);
+    assertEquals(
+        "throw new NullPointerException(foobar(), new Throwable())", writerVisitor.write());
+  }
+
   @Test
   public void writeInstanceofExpr() {
     Variable variable = Variable.builder().setName("x").setType(TypeNode.STRING).build();