[ggj][codegen](2/2)feat: Add HashCode in resource name (#368)

Author: summer-ji-eng

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

@@ -17,6 +17,7 @@
 import com.google.api.core.BetaApi;
 import com.google.api.generator.engine.ast.AnnotationNode;
 import com.google.api.generator.engine.ast.AssignmentExpr;
+import com.google.api.generator.engine.ast.AssignmentOperationExpr;
 import com.google.api.generator.engine.ast.CastExpr;
 import com.google.api.generator.engine.ast.ClassDefinition;
 import com.google.api.generator.engine.ast.CommentStatement;
@@ -274,6 +275,7 @@ private static List<MethodDefinition> createClassMethods(
     javaMethods.add(
         createToStringMethod(templateFinalVarExprs, patternTokenVarExprs, tokenHierarchies));
     javaMethods.add(createEqualsMethod(resourceName, tokenHierarchies, types));
+    javaMethods.add(createHashCodeMethod(tokenHierarchies));
     return javaMethods;
   }
 
@@ -1257,6 +1259,74 @@ private static MethodInvocationExpr createObjectsEqualsForTokenMethodEpxr(
         .build();
   }
 
+  private static MethodDefinition createHashCodeMethod(List<List<String>> tokenHierarchies) {
+    List<Statement> asgmtBody = new ArrayList<>();
+    // code: int h = 1;
+    Variable hVar = Variable.builder().setType(TypeNode.INT).setName("h").build();
+    VariableExpr hVarExpr = VariableExpr.builder().setVariable(hVar).build();
+    ValueExpr hValueExpr =
+        ValueExpr.withValue(PrimitiveValue.builder().setType(TypeNode.INT).setValue("1").build());
+    AssignmentExpr hAssignmentExpr =
+        AssignmentExpr.builder()
+            .setVariableExpr(hVarExpr.toBuilder().setIsDecl(true).build())
+            .setValueExpr(hValueExpr)
+            .build();
+    asgmtBody.add(ExprStatement.withExpr(hAssignmentExpr));
+    // code: h *= 1000003;
+    // code: h ^= Objects.hashCode(...);
+    ValueExpr numValueExpr =
+        ValueExpr.withValue(
+            PrimitiveValue.builder().setType(TypeNode.INT).setValue("1000003").build());
+    AssignmentOperationExpr multiplyAsgmtOpExpr =
+        AssignmentOperationExpr.multiplyAssignmentWithExprs(hVarExpr, numValueExpr);
+    // If it has variants, add the multiply and xor assignment operation exprs for fixedValue.
+    boolean hasVariants = tokenHierarchies.size() > 1;
+    if (hasVariants) {
+      VariableExpr fixedValueVarExpr = FIXED_CLASS_VARS.get("fixedValue");
+      asgmtBody.add(ExprStatement.withExpr(multiplyAsgmtOpExpr));
+      asgmtBody.add(
+          ExprStatement.withExpr(
+              AssignmentOperationExpr.xorAssignmentWithExprs(
+                  hVarExpr, createObjectsHashCodeForVarMethod(fixedValueVarExpr))));
+    }
+    // Add the multiply and xor assignment operation exprs for tokens.
+    Set<String> tokenSet = getTokenSet(tokenHierarchies);
+    tokenSet.stream()
+        .forEach(
+            token -> {
+              VariableExpr tokenVarExpr =
+                  VariableExpr.withVariable(
+                      Variable.builder()
+                          .setName(JavaStyle.toLowerCamelCase(token))
+                          .setType(TypeNode.STRING)
+                          .build());
+              asgmtBody.add(ExprStatement.withExpr(multiplyAsgmtOpExpr));
+              asgmtBody.add(
+                  ExprStatement.withExpr(
+                      AssignmentOperationExpr.xorAssignmentWithExprs(
+                          hVarExpr, createObjectsHashCodeForVarMethod(tokenVarExpr))));
+            });
+
+    return MethodDefinition.builder()
+        .setIsOverride(true)
+        .setScope(ScopeNode.PUBLIC)
+        .setReturnType(TypeNode.INT)
+        .setName("hashCode")
+        .setBody(asgmtBody)
+        .setReturnExpr(hVarExpr)
+        .build();
+  }
+
+  private static MethodInvocationExpr createObjectsHashCodeForVarMethod(VariableExpr varExpr) {
+    // code: Objects.hashCode(varExpr)
+    return MethodInvocationExpr.builder()
+        .setMethodName("hashCode")
+        .setStaticReferenceType(STATIC_TYPES.get("Objects"))
+        .setArguments(varExpr)
+        .setReturnType(TypeNode.INT)
+        .build();
+  }
+
   private static List<ClassDefinition> createNestedBuilderClasses(
       ResourceName resourceName,
       List<List<String>> tokenHierarchies,

src/test/java/com/google/api/generator/gapic/composer/goldens/FoobarName.golden

@@ -264,6 +264,22 @@ public class FoobarName implements ResourceName {
     return false;
   }
 
+  @Override
+  public int hashCode() {
+    int h = 1;
+    h *= 1000003;
+    h ^= Objects.hashCode(fixedValue);
+    h *= 1000003;
+    h ^= Objects.hashCode(project);
+    h *= 1000003;
+    h ^= Objects.hashCode(foobar);
+    h *= 1000003;
+    h ^= Objects.hashCode(variant);
+    h *= 1000003;
+    h ^= Objects.hashCode(barFoo);
+    return h;
+  }
+
   /** Builder for projects/{project}/foobars/{foobar}. */
   public static class Builder {
     private String project;

src/test/java/com/google/api/generator/gapic/composer/goldens/SessionName.golden

@@ -113,6 +113,14 @@ public class SessionName implements ResourceName {
     return false;
   }
 
+  @Override
+  public int hashCode() {
+    int h = 1;
+    h *= 1000003;
+    h ^= Objects.hashCode(session);
+    return h;
+  }
+
   /** Builder for sessions/{session}. */
   public static class Builder {
     private String session;