Add an initial skylark debug server implementation.

Not intending this to be a complete implementation yet.

Among the things still to do:
- officially add support for debugging aspects, rules, etc.,
  with corresponding tests.
- handle breakpoints at return statements (an edge case which
  bypasses Eval).

PiperOrigin-RevId: 199692670

2 files changed, 29 insertions, 8 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/DebugServer.java b/src/main/java/com/google/devtools/build/lib/syntax/DebugServer.java
index f462550797..0238e51959 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/DebugServer.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/DebugServer.java
@@ -14,11 +14,14 @@
 
 package com.google.devtools.build.lib.syntax;
 
+import java.util.function.Function;
+
 /** A debug server interface, called from core skylark code. */
 public interface DebugServer {
 
   /**
-   * Tracks the execution of the given callable object in the debug server.
+   * Executes the given callable and returns its result, while making any skylark evaluation visible
+   * to the debugger. This method should be used to evaluate all debuggable Skylark code.
    *
    * @param env the Skylark execution environment
    * @param threadName the descriptive name of the thread
@@ -29,6 +32,15 @@ public interface DebugServer {
   <T> T runWithDebugging(Environment env, String threadName, DebugCallable<T> callable)
       throws EvalException, InterruptedException;
 
+  /** Shuts down the debug server, closing any open sockets, etc. */
+  void close();
+
+  /**
+   * Returns a custom {@link Eval} supplier used to intercept statement execution to check for
+   * breakpoints.
+   */
+  Function<Environment, Eval> evalOverride();
+
   /** Represents an invocation that will be tracked as a thread by the Skylark debug server. */
   interface DebugCallable<T> {
 
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/DebugServerUtils.java b/src/main/java/com/google/devtools/build/lib/syntax/DebugServerUtils.java
index f653cd994f..808d10704a 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/DebugServerUtils.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/DebugServerUtils.java
@@ -16,10 +16,14 @@ package com.google.devtools.build.lib.syntax;
 
 import com.google.devtools.build.lib.syntax.DebugServer.DebugCallable;
 import java.util.concurrent.atomic.AtomicReference;
-import java.util.function.Function;
 import java.util.function.Supplier;
 
-/** A helper class for enabling/disabling skylark debugging. */
+/**
+ * A helper class for enabling/disabling skylark debugging.
+ *
+ * <p>{@code runWithDebuggingIfEnabled} must be called after {@code initializeDebugServer}, and
+ * before {@code disableDebugging}.
+ */
 public final class DebugServerUtils {
 
   private DebugServerUtils() {}
@@ -30,15 +34,20 @@ public final class DebugServerUtils {
    * Called at the start of a debuggable skylark session to enable debugging. The custom {@link
    * Eval} supplier provided should intercept statement execution to check for breakpoints.
    */
-  public static void initializeDebugServer(
-      DebugServer server, Function<Environment, Eval> evalOverride) {
+  public static void initializeDebugServer(DebugServer server) {
     instance.set(server);
-    Eval.setEvalSupplier(evalOverride);
+    Eval.setEvalSupplier(server.evalOverride());
   }
 
-  /** Called at the end of a debuggable skylark session to disable debugging. */
+  /**
+   * Called at the end of a debuggable skylark session to shut down the debug server and disable
+   * debugging.
+   */
   public static void disableDebugging() {
-    instance.set(null);
+    DebugServer server = instance.getAndSet(null);
+    if (server != null) {
+      server.close();
+    }
     Eval.removeCustomEval();
   }