Index and slice calls are implemented as separate AST nodes rather than special
function calls.
--
MOS_MIGRATED_REVID=133259901
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/SliceExpression.java b/src/main/java/com/google/devtools/build/lib/syntax/SliceExpression.java
new file mode 100644
index 0000000..20804ed
--- /dev/null
+++ b/src/main/java/com/google/devtools/build/lib/syntax/SliceExpression.java
@@ -0,0 +1,114 @@
+// Copyright 2014 The Bazel Authors. 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.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License 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 com.google.devtools.build.lib.syntax;
+
+import com.google.devtools.build.lib.events.Location;
+import java.util.List;
+
+/** Syntax node for an index expression. e.g. obj[field], but not obj[from:to] */
+public final class SliceExpression extends Expression {
+
+ private final Expression obj;
+ private final Expression start;
+ private final Expression end;
+ private final Expression step;
+
+ public SliceExpression(Expression obj, Expression start, Expression end, Expression step) {
+ this.obj = obj;
+ this.start = start;
+ this.end = end;
+ this.step = step;
+ }
+
+ public Expression getObject() {
+ return obj;
+ }
+
+ public Expression getStart() {
+ return start;
+ }
+
+ public Expression getEnd() {
+ return end;
+ }
+
+ public Expression getStep() {
+ return step;
+ }
+
+ @Override
+ public String toString() {
+ return String.format("%s[%s:%s%s]",
+ obj,
+ start,
+ // Omit `end` if it's a literal `None` (default value)
+ ((end instanceof Identifier) && (((Identifier) end).getName().equals("None"))) ? "" : end,
+ // Omit `step` if it's an integer literal `1` (default value)
+ ((step instanceof IntegerLiteral) && (((IntegerLiteral) step).value.equals(1)))
+ ? "" : ":" + step
+ );
+ }
+
+ @Override
+ Object doEval(Environment env) throws EvalException, InterruptedException {
+ Object objValue = obj.eval(env);
+ Object startValue = start.eval(env);
+ Object endValue = end.eval(env);
+ Object stepValue = step.eval(env);
+ return eval(objValue, startValue, endValue, stepValue, getLocation(), env);
+ }
+
+ /**
+ * Returns the result of the given slice, or null if no such slice is supported.
+ */
+ private Object eval(Object objValue, Object startValue, Object endValue, Object stepValue,
+ Location loc, Environment env) throws EvalException {
+ if (objValue instanceof SkylarkList) {
+ SkylarkList<Object> list = (SkylarkList<Object>) objValue;
+ Object slice = list.getSlice(startValue, endValue, stepValue, loc);
+ return SkylarkType.convertToSkylark(slice, env);
+ } else if (objValue instanceof String) {
+ String string = (String) objValue;
+ List<Integer> indices = MethodLibrary.getSliceIndices(startValue, endValue, stepValue,
+ string.length(), loc);
+ char[] result = new char[indices.size()];
+ char[] original = ((String) objValue).toCharArray();
+ int resultIndex = 0;
+ for (int originalIndex : indices) {
+ result[resultIndex] = original[originalIndex];
+ ++resultIndex;
+ }
+ return new String(result);
+ }
+
+ throw new EvalException(
+ loc,
+ Printer.format(
+ "Type %s has no operator [:](%s, %s, %s)",
+ EvalUtils.getDataTypeName(objValue),
+ EvalUtils.getDataTypeName(startValue),
+ EvalUtils.getDataTypeName(endValue),
+ EvalUtils.getDataTypeName(stepValue)));
+ }
+
+ @Override
+ public void accept(SyntaxTreeVisitor visitor) {
+ visitor.visit(this);
+ }
+
+ @Override
+ void validate(ValidationEnvironment env) throws EvalException {
+ obj.validate(env);
+ }
+}
