googleapis · miraleung · Aug 2, 2021 · Aug 2, 2021
diff --git a/src/main/java/com/google/api/generator/engine/ast/ThrowExpr.java b/src/main/java/com/google/api/generator/engine/ast/ThrowExpr.java
@@ -22,6 +22,9 @@
 public abstract class ThrowExpr implements Expr {
   // TODO(miraleung): Refactor with StringObjectValue and possibly with NewObjectExpr.
 
+  @Nullable
+  public abstract Expr throwExpr();
+
   @Override
   public abstract TypeNode type();
 
@@ -42,6 +45,9 @@ public static Builder builder() {
 
   @AutoValue.Builder
   public abstract static class Builder {
+    public abstract Builder setThrowExpr(Expr throwExpr);
+
+    // No-op if setThrowExpr is called.
     public abstract Builder setType(TypeNode type);
 
     public Builder setMessageExpr(String message) {
@@ -53,6 +59,8 @@ public Builder setMessageExpr(String message) {
     public abstract Builder setCauseExpr(Expr expr);
 
     // Private.
+    abstract Expr throwExpr();
+
     abstract TypeNode type();
 
     abstract Expr messageExpr();
@@ -62,6 +70,24 @@ public Builder setMessageExpr(String message) {
     abstract ThrowExpr autoBuild();
 
     public ThrowExpr build() {
+      if (throwExpr() != null) {
+        setType(throwExpr().type());
+        Preconditions.checkState(
+            messageExpr() == null && causeExpr() == null,
+            "Only one of throwExpr or [messageExpr or causeExpr, inclusive] can be present.");
+
+        if (throwExpr() instanceof VariableExpr) {
+          Preconditions.checkState(
+              !((VariableExpr) throwExpr()).isDecl(), "Cannot throw a variable declaration");
+        }
+
+        Preconditions.checkState(
+            TypeNode.isExceptionType(throwExpr().type()),
+            String.format("Only exception types can be thrown, found %s", throwExpr().type()));
+
+        return autoBuild();
+      }
+
       Preconditions.checkState(
           TypeNode.isExceptionType(type()),
           String.format("Type %s must be an exception type", type()));

diff --git a/src/main/java/com/google/api/generator/engine/writer/ImportWriterVisitor.java b/src/main/java/com/google/api/generator/engine/writer/ImportWriterVisitor.java
@@ -231,6 +231,13 @@ public void visit(AnonymousClassExpr anonymousClassExpr) {
   @Override
   public void visit(ThrowExpr throwExpr) {
     throwExpr.type().accept(this);
+    // If throwExpr is present, then messageExpr and causeExpr will not be present. Relies on AST
+    // build-time checks.
+    if (throwExpr.throwExpr() != null) {
+      throwExpr.throwExpr().accept(this);
+      return;
+    }
+
     if (throwExpr.messageExpr() != null) {
       throwExpr.messageExpr().accept(this);
     }

diff --git a/src/main/java/com/google/api/generator/engine/writer/JavaWriterVisitor.java b/src/main/java/com/google/api/generator/engine/writer/JavaWriterVisitor.java
@@ -392,6 +392,13 @@ public void visit(AnonymousClassExpr anonymousClassExpr) {
   public void visit(ThrowExpr throwExpr) {
     buffer.append(THROW);
     space();
+    // If throwExpr is present, then messageExpr and causeExpr will not be present. Relies on AST
+    // build-time checks.
+    if (throwExpr.throwExpr() != null) {
+      throwExpr.throwExpr().accept(this);
+      return;
+    }
+
     buffer.append(NEW);
     space();
     throwExpr.type().accept(this);

diff --git a/src/test/java/com/google/api/generator/engine/ast/ThrowExprTest.java b/src/test/java/com/google/api/generator/engine/ast/ThrowExprTest.java
@@ -14,6 +14,7 @@
 
 package com.google.api.generator.engine.ast;
 
+import static junit.framework.Assert.assertEquals;
 import static org.junit.Assert.assertThrows;
 
 import org.junit.Test;
@@ -24,7 +25,24 @@ public void createThrowExpr_basic() {
     TypeNode npeType = TypeNode.withExceptionClazz(NullPointerException.class);
     ThrowExpr.builder().setType(npeType).build();
     // No exception thrown, we're good.
+  }
 
+  @Test
+  public void createThrowExpr_basicExpr() {
+    TypeNode npeType = TypeNode.withExceptionClazz(NullPointerException.class);
+    VariableExpr throwVarExpr =
+        VariableExpr.builder()
+            .setVariable(
+                Variable.builder()
+                    .setName("e")
+                    .setType(TypeNode.withExceptionClazz(RuntimeException.class))
+                    .build())
+            .build();
+    ThrowExpr throwExpr = ThrowExpr.builder().setThrowExpr(throwVarExpr).build();
+    assertEquals(throwVarExpr.variable().type(), throwExpr.type());
+    // Setting the type doesn't matter.
+    throwExpr = ThrowExpr.builder().setThrowExpr(throwVarExpr).setType(npeType).build();
+    assertEquals(throwVarExpr.variable().type(), throwExpr.type());
   }
 
   @Test
@@ -123,4 +141,75 @@ public void createThrowExpr_messageAndCauseExpr() {
         .build();
     // Successfully created a ThrowExpr.
   }
+
+  @Test
+  public void createThrowExpr_cannotThrowVariableDeclaration() {
+    VariableExpr throwVarExpr =
+        VariableExpr.builder()
+            .setVariable(
+                Variable.builder()
+                    .setName("e")
+                    .setType(TypeNode.withExceptionClazz(RuntimeException.class))
+                    .build())
+            .build();
+    assertThrows(
+        IllegalStateException.class,
+        () ->
+            ThrowExpr.builder()
+                .setThrowExpr(throwVarExpr.toBuilder().setIsDecl(true).build())
+                .build());
+  }
+
+  @Test
+  public void createThrowExpr_cannotThrowNonExceptionTypedExpr() {
+    VariableExpr throwVarExpr =
+        VariableExpr.builder()
+            .setVariable(Variable.builder().setName("str").setType(TypeNode.STRING).build())
+            .build();
+    assertThrows(
+        IllegalStateException.class, () -> ThrowExpr.builder().setThrowExpr(throwVarExpr).build());
+  }
+
+  @Test
+  public void createThrowExpr_cannotHaveThrowVariableAndMessageExprPresent() {
+    Expr messageExpr =
+        MethodInvocationExpr.builder()
+            .setMethodName("foobar")
+            .setReturnType(TypeNode.STRING)
+            .build();
+    VariableExpr throwVarExpr =
+        VariableExpr.builder()
+            .setVariable(
+                Variable.builder()
+                    .setName("e")
+                    .setType(TypeNode.withExceptionClazz(RuntimeException.class))
+                    .build())
+            .build();
+    assertThrows(
+        IllegalStateException.class,
+        () -> ThrowExpr.builder().setThrowExpr(throwVarExpr).setMessageExpr(messageExpr).build());
+  }
+
+  @Test
+  public void createThrowExpr_cannotHaveThrowVariableAndCauseExprPresent() {
+    VariableExpr throwVarExpr =
+        VariableExpr.builder()
+            .setVariable(
+                Variable.builder()
+                    .setName("e")
+                    .setType(TypeNode.withExceptionClazz(RuntimeException.class))
+                    .build())
+            .build();
+    assertThrows(
+        IllegalStateException.class,
+        () ->
+            ThrowExpr.builder()
+                .setThrowExpr(throwVarExpr)
+                .setCauseExpr(
+                    NewObjectExpr.builder()
+                        .setType(
+                            TypeNode.withReference(ConcreteReference.withClazz(Throwable.class)))
+                        .build())
+                .build());
+  }
 }
diff --git a/src/test/java/com/google/api/generator/engine/writer/ImportWriterVisitorTest.java b/src/test/java/com/google/api/generator/engine/writer/ImportWriterVisitorTest.java
@@ -449,6 +449,26 @@ public void writeThrowExprImports_basic() {
     assertEquals("import java.io.IOException;\n\n", writerVisitor.write());
   }
 
+  @Test
+  public void writeThrowExprImports_throwExpr() {
+    Expr exprToThrow =
+        MethodInvocationExpr.builder()
+            .setStaticReferenceType(
+                TypeNode.withReference(ConcreteReference.withClazz(Statement.class)))
+            .setMethodName("createException")
+            .setReturnType(TypeNode.withExceptionClazz(Exception.class))
+            .build();
+
+    TypeNode ignoredExceptionType =
+        TypeNode.withReference(ConcreteReference.withClazz(IOException.class));
+    ThrowExpr throwExpr =
+        ThrowExpr.builder().setType(ignoredExceptionType).setThrowExpr(exprToThrow).build();
+    throwExpr.accept(writerVisitor);
+    assertEquals(
+        LineFormatter.lines("import com.google.api.generator.engine.ast.Statement;\n\n"),
+        writerVisitor.write());
+  }
+
   @Test
   public void writeThrowExprImports_messageExpr() {
     TypeNode npeType = TypeNode.withExceptionClazz(NullPointerException.class);

diff --git a/src/test/java/com/google/api/generator/engine/writer/JavaWriterVisitorTest.java b/src/test/java/com/google/api/generator/engine/writer/JavaWriterVisitorTest.java
@@ -1031,6 +1031,21 @@ public void writeThrowExpr_basic() {
     assertEquals("throw new NullPointerException()", writerVisitor.write());
   }
 
+  @Test
+  public void writeThrowExpr_basicThrowExpr() {
+    Expr exprToThrow =
+        MethodInvocationExpr.builder()
+            .setStaticReferenceType(
+                TypeNode.withReference(ConcreteReference.withClazz(Statement.class)))
+            .setMethodName("createException")
+            .setReturnType(TypeNode.withExceptionClazz(Exception.class))
+            .build();
+
+    ThrowExpr throwExpr = ThrowExpr.builder().setThrowExpr(exprToThrow).build();
+    throwExpr.accept(writerVisitor);
+    assertEquals("throw Statement.createException()", writerVisitor.write());
+  }
+
   @Test
   public void writeThrowExpr_basicWithMessage() {
     TypeNode npeType =