Improve in-code rule-set composition

This commit adds a `SyntaxElement` abstract class that contains several
methods intended for use in constructing rule-sets in code. This class
implements two new interfaces (`ToCondition` and `ToExpression`) to support
converting between types of syntax elements that compose into rule-sets.
The `Condition`, `Parameter`, and `Expression` classes extend this,
allowing all types of ruleset syntax to be composed this way.

Author: kstich

smithy-aws-endpoints/src/main/java/software/amazon/smithy/rulesengine/aws/language/functions/AwsPartition.java

@@ -18,7 +18,7 @@
 import software.amazon.smithy.rulesengine.language.evaluation.type.Type;
 import software.amazon.smithy.rulesengine.language.evaluation.value.Value;
 import software.amazon.smithy.rulesengine.language.syntax.Identifier;
-import software.amazon.smithy.rulesengine.language.syntax.expressions.Expression;
+import software.amazon.smithy.rulesengine.language.syntax.ToExpression;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.ExpressionVisitor;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.FunctionDefinition;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.FunctionNode;
@@ -74,7 +74,7 @@ public static Definition getDefinition() {
      * @param arg1 the region to retrieve partition information from.
      * @return The resulting {@link AwsPartition} function.
      */
-    public static AwsPartition ofExpressions(Expression arg1) {
+    public static AwsPartition ofExpressions(ToExpression arg1) {
         return DEFINITION.createFunction(FunctionNode.ofExpressions(ID, arg1));
     }
 

smithy-aws-endpoints/src/main/java/software/amazon/smithy/rulesengine/aws/language/functions/IsVirtualHostableS3Bucket.java

@@ -10,6 +10,7 @@
 import java.util.regex.Pattern;
 import software.amazon.smithy.rulesengine.language.evaluation.type.Type;
 import software.amazon.smithy.rulesengine.language.evaluation.value.Value;
+import software.amazon.smithy.rulesengine.language.syntax.ToExpression;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.Expression;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.ExpressionVisitor;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.FunctionDefinition;
@@ -45,10 +46,22 @@ public static Definition getDefinition() {
      * @param arg2 whether to allow subdomains.
      * @return The resulting {@link IsVirtualHostableS3Bucket} function.
      */
-    public static IsVirtualHostableS3Bucket ofExpressions(Expression arg1, Expression arg2) {
+    public static IsVirtualHostableS3Bucket ofExpressions(ToExpression arg1, ToExpression arg2) {
         return DEFINITION.createFunction(FunctionNode.ofExpressions(ID, arg1, arg2));
     }
 
+
+    /**
+     * Creates a {@link IsVirtualHostableS3Bucket} function from the given expressions.
+     *
+     * @param arg1 the value to check.
+     * @param arg2 whether to allow subdomains.
+     * @return The resulting {@link IsVirtualHostableS3Bucket} function.
+     */
+    public static IsVirtualHostableS3Bucket ofExpressions(ToExpression arg1, boolean arg2) {
+        return ofExpressions(arg1, Expression.of(arg2));
+    }
+
     @Override
     public <T> T accept(ExpressionVisitor<T> visitor) {
         return visitor.visitLibraryFunction(DEFINITION, getArguments());

smithy-aws-endpoints/src/main/java/software/amazon/smithy/rulesengine/aws/language/functions/ParseArn.java

@@ -14,7 +14,7 @@
 import software.amazon.smithy.rulesengine.language.evaluation.type.Type;
 import software.amazon.smithy.rulesengine.language.evaluation.value.Value;
 import software.amazon.smithy.rulesengine.language.syntax.Identifier;
-import software.amazon.smithy.rulesengine.language.syntax.expressions.Expression;
+import software.amazon.smithy.rulesengine.language.syntax.ToExpression;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.ExpressionVisitor;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.FunctionDefinition;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.FunctionNode;
@@ -56,7 +56,7 @@ public static Definition getDefinition() {
      * @param arg1 the ARN to parse.
      * @return The resulting {@link ParseArn} function.
      */
-    public static ParseArn ofExpressions(Expression arg1) {
+    public static ParseArn ofExpressions(ToExpression arg1) {
         return DEFINITION.createFunction(FunctionNode.ofExpressions(ID, arg1));
     }
 

smithy-aws-endpoints/src/test/java/software/amazon/smithy/rulesengine/aws/language/functions/FunctionsTest.java

@@ -16,8 +16,12 @@ public void awsPartitionOfExpression() {
     @Test
     public void isVirtualHostableS3BucketOfExpression() {
         IsVirtualHostableS3Bucket function = IsVirtualHostableS3Bucket.ofExpressions(
-                Expression.of("foobar"), Expression.of(true));
+                Expression.of("foobar"), true);
         assertThat(function, instanceOf(IsVirtualHostableS3Bucket.class));
+
+        IsVirtualHostableS3Bucket function2 = IsVirtualHostableS3Bucket.ofExpressions(
+                Expression.of("foobar"), Expression.of(true));
+        assertThat(function2, instanceOf(IsVirtualHostableS3Bucket.class));
     }
 
     @Test

smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/SyntaxElement.java

@@ -0,0 +1,124 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.rulesengine.language.syntax;
+
+import software.amazon.smithy.rulesengine.language.syntax.expressions.Expression;
+import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.BooleanEquals;
+import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.GetAttr;
+import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.IsSet;
+import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.IsValidHostLabel;
+import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.Not;
+import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.ParseUrl;
+import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.StringEquals;
+import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.Substring;
+import software.amazon.smithy.rulesengine.language.syntax.rule.Condition;
+import software.amazon.smithy.utils.SmithyInternalApi;
+
+/**
+ * A class that is coercible into {@link Condition}s and {@link Expression}s for
+ * use in composing rule-sets in code.
+ */
+@SmithyInternalApi
+public abstract class SyntaxElement implements ToCondition, ToExpression {
+    /**
+     * Returns a BooleanEquals expression comparing this expression to the provided boolean value.
+     *
+     * @param value the value to compare against.
+     * @return the {@link BooleanEquals} function.
+     */
+    public final BooleanEquals booleanEqual(boolean value) {
+        return BooleanEquals.ofExpressions(toExpression(), Expression.of(value));
+    }
+
+    /**
+     * Returns a StringEquals function of this expression and the given string value.
+     *
+     * @param value the string value to compare this expression to.
+     * @return the {@link StringEquals} function.
+     */
+    public final StringEquals stringEqual(String value) {
+        return StringEquals.ofExpressions(toExpression(), Expression.of(value));
+    }
+
+    /**
+     * Returns a GetAttr function containing the given path string.
+     *
+     * @param path the path.
+     * @return the {@link GetAttr} function.
+     */
+    public final GetAttr getAttr(String path) {
+        return GetAttr.ofExpressions(toExpression(), path);
+    }
+
+    /**
+     * Returns a GetAttr function containing the given identifier.
+     *
+     * @param path the path.
+     * @return the {@link GetAttr} function.
+     */
+    public final GetAttr getAttr(Identifier path) {
+        return GetAttr.ofExpressions(toExpression(), path.toString());
+    }
+
+    /**
+     * Returns an IsSet expression for this instance.
+     *
+     * @return the {@link IsSet} function.
+     */
+    public final IsSet isSet() {
+        return IsSet.ofExpressions(toExpression());
+    }
+
+    /**
+     * Returns an isValidHostLabel expression of this expression.
+     *
+     * @param allowDots whether the UTF-8 {@code .} is considered valid within a host label.
+     * @return the {@link IsValidHostLabel} function.
+     */
+    public final IsValidHostLabel isValidHostLabel(boolean allowDots) {
+        return IsValidHostLabel.ofExpressions(toExpression(), allowDots);
+    }
+
+    /**
+     * Returns a Not expression of this instance.
+     *
+     * @return the {@link Not} function.
+     */
+    public final Not not() {
+        return Not.ofExpressions(toExpression());
+    }
+
+    /**
+     * Returns a parseUrl expression of this expression.
+     *
+     * @return the {@link ParseUrl} function.
+     */
+    public final ParseUrl parseUrl() {
+        return ParseUrl.ofExpressions(toExpression());
+    }
+
+    /**
+     * Returns a Substring expression of this expression.
+     *
+     * @param startIndex the starting index of the string.
+     * @param stopIndex  the ending index of the string.
+     * @param reverse    whether the indexing is should start from end of the string to start.
+     * @return the {@link Substring} function.
+     */
+    public final Substring substring(int startIndex, int stopIndex, boolean reverse) {
+        return Substring.ofExpressions(toExpression(), startIndex, stopIndex, reverse);
+    }
+
+    /**
+     * Converts this expression to a string template.
+     * By default, this implementation returns a {@link RuntimeException}.
+     *
+     * @return the String template.
+     */
+    public String template() {
+        throw new RuntimeException(String.format("cannot convert %s to a string template", this));
+    }
+}

smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/ToCondition.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.rulesengine.language.syntax;
+
+import software.amazon.smithy.rulesengine.language.syntax.rule.Condition;
+import software.amazon.smithy.utils.SmithyInternalApi;
+
+/**
+ * Supplies functionality to be coercible into {@link Condition}s for
+ * use in composing rule-sets in code.
+ */
+@SmithyInternalApi
+public interface ToCondition {
+    /**
+     * Convert this into a condition builder for compositional use.
+     *
+     * @return the condition builder.
+     */
+    Condition.Builder toConditionBuilder();
+
+    /**
+     * Convert this into a condition.
+     *
+     * @return the condition.
+     */
+    default Condition toCondition() {
+        return toConditionBuilder().build();
+    }
+
+    /**
+     * Converts this function into a condition which stores the output in the named result.
+     *
+     * @param result the name of the result parameter.
+     * @return the function as a condition.
+     */
+    default Condition toCondition(String result) {
+        return toConditionBuilder().result(result).build();
+    }
+}

smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/ToExpression.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package software.amazon.smithy.rulesengine.language.syntax;
+
+import software.amazon.smithy.rulesengine.language.syntax.expressions.Expression;
+import software.amazon.smithy.utils.SmithyInternalApi;
+
+/**
+ * Supplies functionality to be coercible into {@link Expression}s for
+ * use in composing rule-sets in code.
+ */
+@SmithyInternalApi
+public interface ToExpression {
+    /**
+     * Convert this into an expression.
+     *
+     * @return the expression.
+     */
+    Expression toExpression();
+}

smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/expressions/Expression.java

@@ -21,10 +21,11 @@
 import software.amazon.smithy.rulesengine.language.evaluation.TypeCheck;
 import software.amazon.smithy.rulesengine.language.evaluation.type.Type;
 import software.amazon.smithy.rulesengine.language.syntax.Identifier;
+import software.amazon.smithy.rulesengine.language.syntax.SyntaxElement;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.FunctionNode;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.GetAttr;
-import software.amazon.smithy.rulesengine.language.syntax.expressions.functions.Not;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.literal.Literal;
+import software.amazon.smithy.rulesengine.language.syntax.rule.Condition;
 import software.amazon.smithy.utils.SmithyUnstableApi;
 
 /**
@@ -33,7 +34,7 @@
  * Expressions are the fundamental building block of the rule language.
  */
 @SmithyUnstableApi
-public abstract class Expression implements FromSourceLocation, ToNode, TypeCheck {
+public abstract class Expression extends SyntaxElement implements FromSourceLocation, ToNode, TypeCheck {
     private final SourceLocation sourceLocation;
     private Type cachedType;
 
@@ -65,15 +66,6 @@ public static Literal of(String value) {
         return getLiteral(StringNode.from(value));
     }
 
-    /**
-     * Negates the current expression.
-     *
-     * @return the negated expression.
-     */
-    public Expression not() {
-        return Not.ofExpressions(this);
-    }
-
     /**
      * Constructs an expression from the provided {@link Node}.
      *
@@ -160,14 +152,14 @@ public Type type() {
         return cachedType;
     }
 
-    /**
-     * Converts this expression to a string template. By default,
-     * this implementation returns a {@link RuntimeException}.
-     *
-     * @return the string template.
-     */
-    public String getTemplate() {
-        throw new RuntimeException(String.format("Cannot convert `%s` to a string template.", this));
+    @Override
+    public Condition.Builder toConditionBuilder() {
+        return Condition.builder().fn(this);
+    }
+
+    @Override
+    public Expression toExpression() {
+        return this;
     }
 
     @Override

smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/expressions/Reference.java

@@ -44,7 +44,7 @@ public Identifier getName() {
     }
 
     @Override
-    public String getTemplate() {
+    public String template() {
         return String.format("{%s}", name);
     }
 

smithy-rules-engine/src/main/java/software/amazon/smithy/rulesengine/language/syntax/expressions/functions/BooleanEquals.java

@@ -9,6 +9,7 @@
 import java.util.List;
 import software.amazon.smithy.rulesengine.language.evaluation.type.Type;
 import software.amazon.smithy.rulesengine.language.evaluation.value.Value;
+import software.amazon.smithy.rulesengine.language.syntax.ToExpression;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.Expression;
 import software.amazon.smithy.rulesengine.language.syntax.expressions.ExpressionVisitor;
 import software.amazon.smithy.utils.SmithyUnstableApi;
@@ -41,10 +42,21 @@ public static Definition getDefinition() {
      * @param arg2 the second argument to compare.
      * @return The resulting {@link BooleanEquals} function.
      */
-    public static BooleanEquals ofExpressions(Expression arg1, Expression arg2) {
+    public static BooleanEquals ofExpressions(ToExpression arg1, ToExpression arg2) {
         return DEFINITION.createFunction(FunctionNode.ofExpressions(ID, arg1, arg2));
     }
 
+    /**
+     * Creates a {@link BooleanEquals} function from the given expressions.
+     *
+     * @param arg1 the first argument to compare.
+     * @param arg2 the second argument to compare.
+     * @return The resulting {@link BooleanEquals} function.
+     */
+    public static BooleanEquals ofExpressions(ToExpression arg1, boolean arg2) {
+        return ofExpressions(arg1, Expression.of(arg2));
+    }
+
     @Override
     public <R> R accept(ExpressionVisitor<R> visitor) {
         return visitor.visitBoolEquals(functionNode.getArguments().get(0), functionNode.getArguments().get(1));