Add a way to construct Frames in a two-step process
RELNOTES: None
PiperOrigin-RevId: 166857589
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Environment.java b/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
index 0ae54ff..2c0a2a6 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Environment.java
@@ -95,20 +95,51 @@
* was defined. When the function is called from other {@code Environment}s (possibly
* simultaneously), that global frame must already be frozen; a new local {@code Frame} is created
* to represent the lexical scope of the function.
+ *
+ * A {@code Frame} can also be constructed in a two-phase process. To do this, call the nullary
+ * constructor to create an uninitialized {@code Frame}, then call {@link #initialize}. It is
+ * illegal to use any other method in-between these two calls, or to call {@link #initialize} on
+ * an already initialized {@code Frame}.
*/
public static final class Frame implements Freezable {
- private final Mutability mutability;
-
+ /**
+ * Final, except that it may be initialized after instantiation. Null mutability indicates that
+ * this Frame is uninitialized.
+ */
@Nullable
- private final Frame parent;
+ private Mutability mutability;
- // If this frame is a global frame, the label for the corresponding target, e.g. //foo:bar.bzl.
+ /** Final, except that it may be initialized after instantiation. */
@Nullable
- private final Label label;
+ private Frame parent;
+
+ /**
+ * If this frame is a global frame, the label for the corresponding target, e.g. {@code
+ * //foo:bar.bzl}.
+ *
+ * <p>Final, except that it may be initialized after instantiation.
+ */
+ @Nullable
+ private Label label;
private final Map<String, Object> bindings;
+ /** Constructs an uninitialized instance; caller must call {@link #initialize} before use. */
+ public Frame() {
+ this.mutability = null;
+ this.parent = null;
+ this.label = null;
+ this.bindings = new LinkedHashMap<>();
+ }
+
+ public Frame(Mutability mutability, @Nullable Frame parent, @Nullable Label label) {
+ this.mutability = Preconditions.checkNotNull(mutability);
+ this.parent = parent;
+ this.label = label;
+ this.bindings = new LinkedHashMap<>();
+ }
+
public Frame(Mutability mutability) {
this(mutability, null, null);
}
@@ -117,15 +148,18 @@
this(mutability, parent, null);
}
- public Frame(Mutability mutability, Frame parent, Label label) {
- this.mutability = mutability;
- this.parent = parent;
- this.label = label;
- this.bindings = new LinkedHashMap<>();
+ private void checkInitialized() {
+ Preconditions.checkNotNull(mutability, "Attempted to use Frame before initializing it");
}
- public Frame(Mutability mutability, Frame parent, Label label, Map<String, Object> bindings) {
- this(mutability, parent, label);
+ public void initialize(
+ Mutability mutability, @Nullable Frame parent,
+ @Nullable Label label, Map<String, Object> bindings) {
+ Preconditions.checkState(this.mutability == null,
+ "Attempted to initialize an already initialized Frame");
+ this.mutability = Preconditions.checkNotNull(mutability);
+ this.parent = parent;
+ this.label = label;
this.bindings.putAll(bindings);
}
@@ -134,6 +168,7 @@
* given value.
*/
public Frame withLabel(Label label) {
+ checkInitialized();
return new Frame(mutability, this, label);
}
@@ -143,12 +178,14 @@
*/
@Override
public Mutability mutability() {
+ checkInitialized();
return mutability;
}
/** Returns the parent {@code Frame}, if it exists. */
@Nullable
public Frame getParent() {
+ checkInitialized();
return parent;
}
@@ -160,6 +197,7 @@
*/
@Nullable
public Label getLabel() {
+ checkInitialized();
return label;
}
@@ -169,6 +207,7 @@
*/
@Nullable
public Label getTransitiveLabel() {
+ checkInitialized();
if (label != null) {
return label;
} else if (parent != null) {
@@ -185,6 +224,7 @@
* invalidated by any subsequent modification to the {@code Frame}'s bindings.
*/
public Map<String, Object> getBindings() {
+ checkInitialized();
return Collections.unmodifiableMap(bindings);
}
@@ -193,6 +233,7 @@
* taking into account shadowing precedence.
*/
public Map<String, Object> getTransitiveBindings() {
+ checkInitialized();
// Can't use ImmutableMap.Builder because it doesn't allow duplicates.
HashMap<String, Object> collectedBindings = new HashMap<>();
accumulateTransitiveBindings(collectedBindings);
@@ -200,6 +241,7 @@
}
private void accumulateTransitiveBindings(Map<String, Object> accumulator) {
+ checkInitialized();
// Put parents first, so child bindings take precedence.
if (parent != null) {
parent.accumulateTransitiveBindings(accumulator);
@@ -217,6 +259,7 @@
* @return the value bound to the variable, or null if no binding is found
*/
public Object get(String varname) {
+ checkInitialized();
if (bindings.containsKey(varname)) {
return bindings.get(varname);
}
@@ -238,6 +281,7 @@
*/
public void put(Environment env, String varname, Object value)
throws MutabilityException {
+ checkInitialized();
Mutability.checkMutable(this, env.mutability());
bindings.put(varname, value);
}
@@ -247,13 +291,18 @@
* be part of the public interface.
*/
void remove(Environment env, String varname) throws MutabilityException {
+ checkInitialized();
Mutability.checkMutable(this, env.mutability());
bindings.remove(varname);
}
@Override
public String toString() {
- return String.format("<Frame%s>", mutability());
+ if (mutability == null) {
+ return "<Uninitialized Frame>";
+ } else {
+ return String.format("<Frame%s>", mutability());
+ }
}
}
