[operators][integrate]feat!: Integrate OperationExpr into GeneralForStatement

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

@@ -22,19 +22,11 @@
 
 @AutoValue
 public abstract class GeneralForStatement implements Statement {
-  public abstract Expr initializationExpr();
+  public abstract AssignmentExpr initializationExpr();
 
-  // TODO(summerji): Integrate OperationExpr here. Start by uncommenting the following section to
-  // replace the localVariableExpr and maxSizeExpr getters after it.
-  /*
-  // Uses the same terminology as https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html.
   public abstract Expr terminationExpr();
-  public abstract Expr incrementExpr();
-  */
-
-  public abstract VariableExpr localVariableExpr();
 
-  public abstract Expr maxSizeExpr();
+  public abstract Expr incrementExpr();
 
   public abstract ImmutableList<Statement> body();
 
@@ -43,14 +35,26 @@ public void accept(AstNodeVisitor visitor) {
     visitor.visit(this);
   }
 
-  // Convenience wrapper.
+  // incrementWith is convenience wrapper to generate index-base for-loop with lower and upper bound
+  // and post increment on variable, like code in ```for (int i = 0; i < getMax(); i++) {..}```
+  // TODO (developer): Add more convenience wrapper for the future generation needs.
   public static GeneralForStatement incrementWith(
-      VariableExpr variableExpr, Expr maxSizeExpr, List<Statement> body) {
-    // TODO(summerji): Do some integration here, in JavaWriterVisitor, in ImportWriterVisitor, and
-    // add more tests.
+      VariableExpr localVariableExpr,
+      ValueExpr initialValueExpr,
+      Expr maxSizeExpr,
+      List<Statement> body) {
     return builder()
-        .setLocalVariableExpr(variableExpr.toBuilder().setIsDecl(false).build())
-        .setMaxSizeExpr(maxSizeExpr)
+        .setInitializationExpr(
+            AssignmentExpr.builder()
+                .setVariableExpr(localVariableExpr)
+                .setValueExpr(initialValueExpr)
+                .build())
+        .setTerminationExpr(
+            RelationalOperationExpr.lessThanWithExprs(
+                localVariableExpr.toBuilder().setIsDecl(false).build(), maxSizeExpr))
+        .setIncrementExpr(
+            UnaryOperationExpr.postfixIncrementWithExpr(
+                localVariableExpr.toBuilder().setIsDecl(false).build()))
         .setBody(body)
         .build();
   }
@@ -61,22 +65,24 @@ public static Builder builder() {
 
   @AutoValue.Builder
   public abstract static class Builder {
-    public abstract Builder setInitializationExpr(Expr initializationExpr);
-
-    public abstract Builder setBody(List<Statement> body);
-
-    // Private.
-    abstract Builder setLocalVariableExpr(VariableExpr variableExpr);
-
-    abstract Builder setMaxSizeExpr(Expr maxSizeExpr);
-
-    abstract VariableExpr localVariableExpr();
+    // Private setter.
+    abstract Builder setInitializationExpr(AssignmentExpr initializationExpr);
+    // Private setter.
+    abstract Builder setTerminationExpr(Expr terminationExpr);
+    // Private setter.
+    abstract Builder setIncrementExpr(Expr incrementExpr);
+    // Private setter.
+    abstract Builder setBody(List<Statement> body);
 
     abstract GeneralForStatement autoBuild();
 
     // Type-checking will be done in the sub-expressions.
     public GeneralForStatement build() {
-      VariableExpr varExpr = localVariableExpr();
+      GeneralForStatement generalForStatement = autoBuild();
+      AssignmentExpr initializationExpr = generalForStatement.initializationExpr();
+      Expr terminationExpr = generalForStatement.terminationExpr();
+      Expr incrementExpr = generalForStatement.incrementExpr();
+      VariableExpr varExpr = initializationExpr.variableExpr();
       Preconditions.checkState(
           varExpr.scope().equals(ScopeNode.LOCAL),
           String.format(
@@ -87,16 +93,18 @@ public GeneralForStatement build() {
           String.format(
               "Variable %s in a general for-loop cannot be static or final",
               varExpr.variable().identifier().name()));
-      setInitializationExpr(
-          AssignmentExpr.builder()
-              .setVariableExpr(varExpr.toBuilder().setIsDecl(true).build())
-              .setValueExpr(
-                  ValueExpr.withValue(
-                      PrimitiveValue.builder().setValue("0").setType(TypeNode.INT).build()))
-              .build());
-      // TODO(summerji): Remove the following two lines.
-      // This temporary workaround will be removed soon, so it doesn't need a test.
-      setLocalVariableExpr(varExpr.toBuilder().setIsDecl(false).build());
+      Preconditions.checkState(
+          terminationExpr.type().equals(TypeNode.BOOLEAN),
+          "Terminal expression %s must be boolean-type expression.");
+      Preconditions.checkState(
+          (incrementExpr instanceof MethodInvocationExpr)
+              || (incrementExpr instanceof AssignmentExpr)
+              || (incrementExpr instanceof AssignmentOperationExpr)
+              // TODO(developer): Currently we only support postIncrement (i++), please add
+              // postDecrement, prefixIncrement, prefixIncrement if needs.
+              || (incrementExpr instanceof UnaryOperationExpr
+                  && ((UnaryOperationExpr) incrementExpr).isPostfixIncrement()),
+          "Increment expression %s must be either a method invocation, assignment, or unary post-fix operation expression.");
       return autoBuild();
     }
   }

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

@@ -281,8 +281,8 @@ public void visit(ForStatement forStatement) {
   @Override
   public void visit(GeneralForStatement generalForStatement) {
     generalForStatement.initializationExpr().accept(this);
-    generalForStatement.localVariableExpr().accept(this);
-    generalForStatement.maxSizeExpr().accept(this);
+    generalForStatement.terminationExpr().accept(this);
+    generalForStatement.incrementExpr().accept(this);
     statements(generalForStatement.body());
   }
 

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

@@ -540,17 +540,11 @@ public void visit(GeneralForStatement generalForStatement) {
     semicolon();
     space();
 
-    generalForStatement.localVariableExpr().accept(this);
-    space();
-    buffer.append(LEFT_ANGLE);
-    space();
-    generalForStatement.maxSizeExpr().accept(this);
+    generalForStatement.terminationExpr().accept(this);
     semicolon();
     space();
 
-    generalForStatement.localVariableExpr().accept(this);
-    // TODO(summerji): Remove the following temporary workaround.
-    buffer.append("++");
+    generalForStatement.incrementExpr().accept(this);
     rightParen();
     space();
     leftBrace();

src/main/java/com/google/api/generator/gapic/composer/BatchingDescriptorComposer.java

@@ -354,10 +354,16 @@ private static MethodDefinition createSplitResponseMethod(
       // TODO(miraleung): Increment batchMessageIndexVarExpr.
 
       VariableExpr forIndexVarExpr =
-          VariableExpr.withVariable(Variable.builder().setType(TypeNode.INT).setName("i").build());
+          VariableExpr.builder()
+              .setIsDecl(true)
+              .setVariable(Variable.builder().setType(TypeNode.INT).setName("i").build())
+              .build();
+      ValueExpr initValueExpr =
+          ValueExpr.withValue(PrimitiveValue.builder().setValue("0").setType(TypeNode.INT).build());
       GeneralForStatement innerSubresponseForStatement =
           GeneralForStatement.incrementWith(
               forIndexVarExpr,
+              initValueExpr,
               subresponseCountVarExpr,
               innerSubresponseForExprs.stream()
                   .map(e -> ExprStatement.withExpr(e))