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Add ability to serialize the JMESPath AST #1059

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merged 2 commits into from
Jan 19, 2022
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Add ability to serialize the JMESPath AST #1059

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6d6bd13
Add ability to serialize the JMESPath AST
mtdowling Jan 14, 2022
135e351
Update smithy-jmespath/src/main/java/software/amazon/smithy/jmespath/…
mtdowling Jan 18, 2022
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383 changes: 383 additions & 0 deletions smithy-jmespath/src/main/java/software/amazon/smithy/jmespath/ExpressionSerializer.java
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Original file line number Diff line number Diff line change
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/*
* Copyright 2022 Amazon.com, Inc. or its affiliates. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License").
* You may not use this file except in compliance with the License.
* A copy of the License is located at
*
* http://aws.amazon.com/apache2.0
*
* or in the "license" file accompanying this file. This file is distributed
* on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
* express or implied. See the License for the specific language governing
* permissions and limitations under the License.
*/

package software.amazon.smithy.jmespath;

import java.util.Map;
import java.util.Set;
import software.amazon.smithy.jmespath.ast.AndExpression;
import software.amazon.smithy.jmespath.ast.BinaryExpression;
import software.amazon.smithy.jmespath.ast.ComparatorExpression;
import software.amazon.smithy.jmespath.ast.CurrentExpression;
import software.amazon.smithy.jmespath.ast.ExpressionTypeExpression;
import software.amazon.smithy.jmespath.ast.FieldExpression;
import software.amazon.smithy.jmespath.ast.FilterProjectionExpression;
import software.amazon.smithy.jmespath.ast.FlattenExpression;
import software.amazon.smithy.jmespath.ast.FunctionExpression;
import software.amazon.smithy.jmespath.ast.IndexExpression;
import software.amazon.smithy.jmespath.ast.LiteralExpression;
import software.amazon.smithy.jmespath.ast.MultiSelectHashExpression;
import software.amazon.smithy.jmespath.ast.MultiSelectListExpression;
import software.amazon.smithy.jmespath.ast.NotExpression;
import software.amazon.smithy.jmespath.ast.ObjectProjectionExpression;
import software.amazon.smithy.jmespath.ast.OrExpression;
import software.amazon.smithy.jmespath.ast.ProjectionExpression;
import software.amazon.smithy.jmespath.ast.SliceExpression;
import software.amazon.smithy.jmespath.ast.Subexpression;

/**
* Serializes the JMESPath expression AST back to a JMESPath expression.
*/
public final class ExpressionSerializer {

/**
* Serialize the given JMESPath expression to a string.
*
* @param expression JMESPath expression to serialize.
* @return Returns the serialized expression.
*/
public String serialize(JmespathExpression expression) {
StringBuilder builder = new StringBuilder();
Visitor visitor = new Visitor(builder);
expression.accept(visitor);
return builder.toString();
}

private static final class Visitor implements ExpressionVisitor<Void> {
private final StringBuilder builder;

Visitor(StringBuilder builder) {
this.builder = builder;
}

@Override
public Void visitComparator(ComparatorExpression expression) {
// e.g.: foo > bar
expression.getLeft().accept(this);
builder.append(' ');
builder.append(expression.getComparator());
builder.append(' ');
expression.getRight().accept(this);
return null;
}

@Override
public Void visitCurrentNode(CurrentExpression expression) {
builder.append('@');
return null;
}

@Override
public Void visitExpressionType(ExpressionTypeExpression expression) {
// e.g.: &(foo.bar)
builder.append("&(");
expression.getExpression().accept(this);
builder.append(')');
return null;
}

@Override
public Void visitFlatten(FlattenExpression expression) {
// e.g.: foo[]
expression.getExpression().accept(this);
builder.append("[]");
return null;
}

@Override
public Void visitFunction(FunctionExpression expression) {
// e.g.: some_function(@, foo)
builder.append(expression.getName());
builder.append('(');
for (int i = 0; i < expression.getArguments().size(); i++) {
expression.getArguments().get(i).accept(this);
if (i < expression.getArguments().size() - 1) {
builder.append(", ");
}
}
builder.append(')');
return null;
}

@Override
public Void visitField(FieldExpression expression) {
// Always quote fields: "foo"
builder.append('"');
builder.append(sanitizeString(expression.getName(), false));
builder.append('"');
return null;
}

private String sanitizeString(String str, boolean escapeBackticks) {
String result = str.replace("\\", "\\\\").replace("\"", "\\\"");
if (escapeBackticks) {
result = result.replace("`", "\\`");
}
return result;
}

@Override
public Void visitIndex(IndexExpression expression) {
// e.g.: [1]
builder.append('[').append(expression.getIndex()).append(']');
return null;
}

@Override
public Void visitLiteral(LiteralExpression expression) {
// e.g.: `[true]`
visitLiteral(expression, false);
return null;
}

private void visitLiteral(LiteralExpression expression, boolean nestedInsideLiteral) {
if (!nestedInsideLiteral) {
builder.append('`');
}

switch (expression.getType()) {
case NUMBER:
builder.append(expression.expectNumberValue());
break;
case NULL:
case ANY: // treat "any" like null
builder.append("null");
break;
case ARRAY:
builder.append('[');
int ai = 0;
for (Object value : expression.expectArrayValue()) {
LiteralExpression exp = LiteralExpression.from(value);
visitLiteral(exp, true);
if (ai++ < expression.expectArrayValue().size() - 1) {
builder.append(", ");
}
}
builder.append(']');
break;
case OBJECT:
builder.append('{');
int oi = 0;
Set<Map.Entry<String, Object>> objectEntries = expression.expectObjectValue().entrySet();
for (Map.Entry<String, Object> objectEntry : objectEntries) {
builder.append('"')
.append(sanitizeString(objectEntry.getKey(), true))
.append("\": ");
LiteralExpression exp = LiteralExpression.from(objectEntry.getValue());
visitLiteral(exp, true);
if (oi++ < objectEntries.size() - 1) {
builder.append(", ");
}
}
builder.append('}');
break;
case STRING:
builder.append('"')
.append(sanitizeString(expression.expectStringValue(), true))
.append('"');
break;
case BOOLEAN:
builder.append(expression.expectBooleanValue());
break;
case EXPRESSION:
// fall-through
default:
throw new JmespathException("Unable to serialize literal runtime value: " + expression);
}

if (!nestedInsideLiteral) {
builder.append('`');
}
}

@Override
public Void visitMultiSelectList(MultiSelectListExpression expression) {
// e.g.: [foo, bar[].baz]
builder.append('[');
for (int i = 0; i < expression.getExpressions().size(); i++) {
expression.getExpressions().get(i).accept(this);
if (i < expression.getExpressions().size() - 1) {
builder.append(", ");
}
}
builder.append(']');
return null;
}

@Override
public Void visitMultiSelectHash(MultiSelectHashExpression expression) {
// e.g.: {foo: `true`, bar: bar}
builder.append('{');
int i = 0;
for (Map.Entry<String, JmespathExpression> entry : expression.getExpressions().entrySet()) {
builder.append('"').append(sanitizeString(entry.getKey(), false)).append("\": ");
entry.getValue().accept(this);
if (i < expression.getExpressions().entrySet().size() - 1) {
builder.append(", ");
}
i++;
}
builder.append('}');
return null;
}

@Override
public Void visitAnd(AndExpression expression) {
// e.g.: (a && b)
builder.append('(');
expression.getLeft().accept(this);
builder.append(" && ");
expression.getRight().accept(this);
builder.append(')');
return null;
}

@Override
public Void visitOr(OrExpression expression) {
// e.g.: (a || b)
builder.append('(');
expression.getLeft().accept(this);
builder.append(" || ");
expression.getRight().accept(this);
builder.append(')');
return null;
}

@Override
public Void visitNot(NotExpression expression) {
// e.g.: !(foo.bar)
builder.append("!(");
expression.getExpression().accept(this);
builder.append(')');
return null;
}

@Override
public Void visitProjection(ProjectionExpression expression) {
if (!(expression.getLeft() instanceof CurrentExpression)) {
expression.getLeft().accept(this);
}

// Without this check, [::1].a would be reserialized into [::-1][*]."a",
// which is equivalent, but convoluted.
if (!(expression.getLeft() instanceof SliceExpression)) {
// Flatten expressions, when parsed, inherently create a projection. Unroll
// that here.
if (!(expression.getLeft() instanceof FlattenExpression)) {
builder.append("[*]");
}
}

// Avoid unnecessary addition of extracting the current node.
// We add the current node in projections if there's no RHS.
if (!(expression.getRight() instanceof CurrentExpression)) {
// Add a "." if the right hand side needs it.
if (rhsNeedsDot(expression.getRight())) {
builder.append('.');
}
expression.getRight().accept(this);
}

return null;
}

@Override
public Void visitFilterProjection(FilterProjectionExpression expression) {
// e.g.: foo[?bar == `10`].baz
// Don't emit a pointless the current node select.
if (!(expression.getLeft() instanceof CurrentExpression)) {
expression.getLeft().accept(this);
}

builder.append("[?");
expression.getComparison().accept(this);
builder.append(']');

// Avoid unnecessary addition of extracting the current node.
if (!(expression.getRight() instanceof CurrentExpression)) {
// Add a "." if the right hand side needs it.
if (rhsNeedsDot(expression.getRight())) {
builder.append('.');
}
expression.getRight().accept(this);
}

return null;
}

@Override
public Void visitObjectProjection(ObjectProjectionExpression expression) {
// Avoid the unnecessary "@.*" by just emitting "*".
if (!(expression.getLeft() instanceof CurrentExpression)) {
expression.getLeft().accept(this);
builder.append(".*");
} else {
builder.append('*');
}

// Avoid unnecessary addition of extracting the current node.
// We add the current node in projections if there's no RHS.
if (!(expression.getRight() instanceof CurrentExpression)) {
// Add a "." if the right hand side needs it.
if (rhsNeedsDot(expression.getRight())) {
builder.append('.');
}
expression.getRight().accept(this);
}

return null;
}

@Override
public Void visitSlice(SliceExpression expression) {
// e.g.: [0::1], [0:1:2], etc
builder.append('[');
expression.getStart().ifPresent(builder::append);
builder.append(':');
expression.getStop().ifPresent(builder::append);
builder.append(':');
builder.append(expression.getStep());
builder.append(']');
return null;
}

@Override
public Void visitSubexpression(Subexpression expression) {
// e.g.: "foo"."bar", "foo" | "bar"
expression.getLeft().accept(this);

if (expression.isPipe()) {
// pipe has a different precedence than dot, so this is important.
builder.append(" | ");
} else if (rhsNeedsDot(expression.getRight())) {
builder.append('.');
}

expression.getRight().accept(this);
return null;
}

// These expression need to be preceded by a "." in a binary expression.
private boolean rhsNeedsDot(JmespathExpression expression) {
return expression instanceof FieldExpression
|| expression instanceof MultiSelectHashExpression
|| expression instanceof MultiSelectListExpression
|| expression instanceof ObjectProjectionExpression
|| expression instanceof FunctionExpression
|| (expression instanceof BinaryExpression
&& rhsNeedsDot(((BinaryExpression) expression).getLeft()));
}
}
}
2 changes: 1 addition & 1 deletion smithy-jmespath/src/main/java/software/amazon/smithy/jmespath/Parser.java
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Original file line number Diff line number Diff line change
Expand Up @@ -170,7 +170,7 @@ private JmespathExpression led(JmespathExpression left) {
case AND: // Example: a && b
return new AndExpression(left, expression(token.type.lbp), token.line, token.column);
case PIPE: // Example: a | b
return new Subexpression(left, expression(token.type.lbp), token.line, token.column);
return new Subexpression(left, expression(token.type.lbp), token.line, token.column, true);
case FILTER: // Example: a[?foo == bar]
return parseFilter(left);
case LBRACKET:
Expand Down
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