Add computation visitors

* Fix immutable fields
* Fix .gitignore
* Re-add Guava dependency

Author: rebecca-odonoghue

.gitignore

@@ -7,9 +7,9 @@
 **/.kotlin
 
 # Build dirs
-rsvp/build
-rsvp/bin
-rsvp/app/build
-rsvp/app/bin
-rsvp/policy-ast/build
-rsvp/policy-ast/bin
+/rsvp/build
+/rsvp/bin
+/rsvp/app/build
+/rsvp/app/bin
+/rsvp/policy-ast/build
+/rsvp/policy-ast/bin

rsvp/README.md

@@ -49,10 +49,18 @@ Before building this project, you will need to build and deploy CedarJava locall
 
 ## Implement a new policy visitor
 
-Visitor classes can be found in the `uq.pac.rsvp.policy.ast.visitor` package. Visitors that don't need to visit every node type but would still like to traverse the entire tree can extend the `PolicyVisitorImpl` class. Otherwise, interface `PolicyVisitor` can be implemented directly.
+Visitor classes can be found in the `uq.pac.rsvp.policy.ast.visitor` package.
 
-The JSON schema for the serialised Java AST is defined in `lib/src/main/resources/ast.schema.json`. A schema for the Cedar JSON
-Schema syntax can be found in the [Cedar VSCode Extension repository](https://raw.githubusercontent.com/cedar-policy/vscode-cedar/refs/heads/main/schemas/cedarschema.schema.json).
+There are two types of visitors, visitors that return `void` from their visit methods, and visitors that return a
+generic typed value. Visitors that return void should implement `PolicyVisitor` or `SchemaVisitor`. If they don't
+need to visit every node type but would still like to traverse the entire tree, `PolicyVisitorImpl` or
+`SchemaVisitorImpl` can be extended instead.
+
+Visitors that return a value from their `visit` methods should implement `PolicyComputationVisitor` or
+`SchemaComputationVisitor` and call the generic `compute` method on each `AST` node, rather than `visit`.
+
+The JSON schema for the serialised Java AST is defined in `lib/src/main/resources/ast.schema.json`. A
+schema for the Cedar JSON schema syntax can be found in the [Cedar VSCode Extension repository](https://raw.githubusercontent.com/cedar-policy/vscode-cedar/refs/heads/main/schemas/cedarschema.schema.json).
 
 ## Using the policy AST library in another project
 

rsvp/build.gradle

@@ -10,10 +10,9 @@ allprojects {
     dependencies {
         // Custom cedar-java fork (https://github.com/rebecca-odonoghue/cedar-java)
         implementation 'com.cedarpolicy:cedar-java:3.1.2-rsvp:uber'
-
         implementation 'com.google.code.gson:gson:2.13.2'
-
         implementation 'com.fasterxml.jackson.core:jackson-databind:2.20.0'
+        implementation libs.guava
 
         // Use JUnit Jupiter for testing.
         testImplementation libs.junit.jupiter

rsvp/policy-ast/src/main/java/uq/pac/rsvp/policy/ast/Policy.java

@@ -3,6 +3,7 @@
 import com.google.gson.annotations.SerializedName;
 
 import uq.pac.rsvp.policy.ast.expr.Expression;
+import uq.pac.rsvp.policy.ast.visitor.PolicyComputationVisitor;
 import uq.pac.rsvp.policy.ast.visitor.PolicyVisitor;
 
 public class Policy {
@@ -42,6 +43,10 @@ public void accept(PolicyVisitor visitor) {
         visitor.visitPolicy(this);
     }
 
+    public <T> T compute(PolicyComputationVisitor<T> visitor) {
+        return visitor.visitPolicy(this);
+    }
+
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();

rsvp/policy-ast/src/main/java/uq/pac/rsvp/policy/ast/expr/BinaryExpression.java

@@ -5,6 +5,7 @@
 import com.google.gson.annotations.SerializedName;
 
 import uq.pac.rsvp.policy.ast.SourceLoc;
+import uq.pac.rsvp.policy.ast.visitor.PolicyComputationVisitor;
 import uq.pac.rsvp.policy.ast.visitor.PolicyVisitor;
 
 public class BinaryExpression extends Expression {
@@ -84,6 +85,11 @@ public void accept(PolicyVisitor visitor) {
         visitor.visitBinaryExpr(this);
     }
 
+    @Override
+    public <T> T compute(PolicyComputationVisitor<T> visitor) {
+        return visitor.visitBinaryExpr(this);
+    }
+
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();

rsvp/policy-ast/src/main/java/uq/pac/rsvp/policy/ast/expr/BooleanExpression.java

@@ -3,6 +3,7 @@
 import static uq.pac.rsvp.policy.ast.expr.Expression.ExprType.BooleanLiteral;
 
 import uq.pac.rsvp.policy.ast.SourceLoc;
+import uq.pac.rsvp.policy.ast.visitor.PolicyComputationVisitor;
 import uq.pac.rsvp.policy.ast.visitor.PolicyVisitor;;
 
 public class BooleanExpression extends Expression {
@@ -23,6 +24,11 @@ public void accept(PolicyVisitor visitor) {
         visitor.visitBooleanExpr(this);
     }
 
+    @Override
+    public <T> T compute(PolicyComputationVisitor<T> visitor) {
+        return visitor.visitBooleanExpr(this);
+    }
+
     @Override
     public String toString() {
         return String.valueOf(value);

rsvp/policy-ast/src/main/java/uq/pac/rsvp/policy/ast/expr/CallExpression.java

@@ -5,6 +5,7 @@
 import java.util.List;
 
 import uq.pac.rsvp.policy.ast.SourceLoc;
+import uq.pac.rsvp.policy.ast.visitor.PolicyComputationVisitor;
 import uq.pac.rsvp.policy.ast.visitor.PolicyVisitor;
 
 public class CallExpression extends Expression {
@@ -43,6 +44,11 @@ public void accept(PolicyVisitor visitor) {
         visitor.visitCallExpr(this);
     }
 
+    @Override
+    public <T> T compute(PolicyComputationVisitor<T> visitor) {
+        return visitor.visitCallExpr(this);
+    }
+
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();

rsvp/policy-ast/src/main/java/uq/pac/rsvp/policy/ast/expr/ConditionalExpression.java

@@ -5,6 +5,7 @@
 import com.google.gson.annotations.SerializedName;
 
 import uq.pac.rsvp.policy.ast.SourceLoc;
+import uq.pac.rsvp.policy.ast.visitor.PolicyComputationVisitor;
 import uq.pac.rsvp.policy.ast.visitor.PolicyVisitor;
 
 public class ConditionalExpression extends Expression {
@@ -40,6 +41,11 @@ public void accept(PolicyVisitor visitor) {
         visitor.visitConditionalExpr(this);
     }
 
+    @Override
+    public <T> T compute(PolicyComputationVisitor<T> visitor) {
+        return visitor.visitConditionalExpr(this);
+    }
+
     @Override
     public String toString() {
         StringBuilder sb = new StringBuilder();

rsvp/policy-ast/src/main/java/uq/pac/rsvp/policy/ast/expr/EntityExpression.java

@@ -13,6 +13,7 @@
 import com.google.gson.JsonElement;
 
 import uq.pac.rsvp.policy.ast.SourceLoc;
+import uq.pac.rsvp.policy.ast.visitor.PolicyComputationVisitor;
 import uq.pac.rsvp.policy.ast.visitor.PolicyVisitor;;
 
 public class EntityExpression extends Expression {
@@ -41,6 +42,11 @@ public void accept(PolicyVisitor visitor) {
         visitor.visitEntityExpr(this);
     }
 
+    @Override
+    public <T> T compute(PolicyComputationVisitor<T> visitor) {
+        return visitor.visitEntityExpr(this);
+    }
+
     @Override
     public String toString() {
         return String.join("::", path) + "::\"" + eid + "\"";

rsvp/policy-ast/src/main/java/uq/pac/rsvp/policy/ast/expr/Expression.java

@@ -10,6 +10,7 @@
 import com.google.gson.annotations.SerializedName;
 
 import uq.pac.rsvp.policy.ast.SourceLoc;
+import uq.pac.rsvp.policy.ast.visitor.PolicyComputationVisitor;
 import uq.pac.rsvp.policy.ast.visitor.PolicyVisitor;
 
 public abstract class Expression {
@@ -68,6 +69,8 @@ protected Expression(ExprType type, SourceLoc source) {
 
     public abstract void accept(PolicyVisitor visitor);
 
+    public abstract <T> T compute(PolicyComputationVisitor<T> visitor);
+
     public final SourceLoc getSourceLoc() {
         return source != null ? source : MISSING_SRC;
     }