Add --toolchain_resolution_debug option to give more information about

toolchain selection.

Fixes #3431.

Change-Id: Ia38415575b6a121cbb6a028bfc0276691cd11b6d
PiperOrigin-RevId: 163196646

1 files changed, 50 insertions, 5 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ToolchainResolutionFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/ToolchainResolutionFunction.java
index 28a6ebe0ca..410578f497 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ToolchainResolutionFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ToolchainResolutionFunction.java
@@ -17,11 +17,14 @@ package com.google.devtools.build.lib.skyframe;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
 import com.google.devtools.build.lib.analysis.PlatformConfiguration;
+import com.google.devtools.build.lib.analysis.PlatformOptions;
 import com.google.devtools.build.lib.analysis.config.BuildConfiguration;
 import com.google.devtools.build.lib.analysis.platform.ConstraintValueInfo;
 import com.google.devtools.build.lib.analysis.platform.DeclaredToolchainInfo;
 import com.google.devtools.build.lib.analysis.platform.PlatformInfo;
 import com.google.devtools.build.lib.cmdline.Label;
+import com.google.devtools.build.lib.events.Event;
+import com.google.devtools.build.lib.events.EventHandler;
 import com.google.devtools.build.lib.packages.NoSuchThingException;
 import com.google.devtools.build.lib.skyframe.ConfiguredTargetFunction.ConfiguredValueCreationException;
 import com.google.devtools.build.lib.skyframe.RegisteredToolchainsFunction.InvalidTargetException;
@@ -74,12 +77,14 @@ public class ToolchainResolutionFunction implements SkyFunction {
     }
 
     // Find the right one.
+    boolean debug = configuration.getOptions().get(PlatformOptions.class).toolchainResolutionDebug;
     DeclaredToolchainInfo toolchain =
         resolveConstraints(
             key.toolchainType(),
             key.execPlatform(),
             key.targetPlatform(),
-            toolchains.registeredToolchains());
+            toolchains.registeredToolchains(),
+            debug ? env.getListener() : null);
 
     if (toolchain == null) {
       throw new ToolchainResolutionFunctionException(
@@ -93,35 +98,75 @@ public class ToolchainResolutionFunction implements SkyFunction {
       Label toolchainType,
       PlatformInfo execPlatform,
       PlatformInfo targetPlatform,
-      ImmutableList<DeclaredToolchainInfo> toolchains) {
+      ImmutableList<DeclaredToolchainInfo> toolchains,
+      @Nullable EventHandler eventHandler) {
+
+    debugMessage(eventHandler, "Looking for toolchain of type %s...", toolchainType);
     for (DeclaredToolchainInfo toolchain : toolchains) {
       // Make sure the type matches.
       if (!toolchain.toolchainType().equals(toolchainType)) {
         continue;
       }
-      if (!checkConstraints(toolchain.execConstraints(), execPlatform)) {
+      debugMessage(eventHandler, "  Considering toolchain %s...", toolchain.toolchainLabel());
+      if (!checkConstraints(eventHandler, toolchain.execConstraints(), "execution", execPlatform)) {
+        debugMessage(
+            eventHandler,
+            "  Rejected toolchain %s, because of execution platform mismatch",
+            toolchain.toolchainLabel());
         continue;
       }
-      if (!checkConstraints(toolchain.targetConstraints(), targetPlatform)) {
+      if (!checkConstraints(
+          eventHandler, toolchain.targetConstraints(), "target", targetPlatform)) {
+        debugMessage(
+            eventHandler,
+            "  Rejected toolchain %s, because of target platform mismatch",
+            toolchain.toolchainLabel());
         continue;
       }
 
+      debugMessage(eventHandler, "  Selected toolchain %s", toolchain.toolchainLabel());
       return toolchain;
     }
 
+    debugMessage(eventHandler, "  No toolchain found");
     return null;
   }
 
   /**
+   * Helper method to print a debugging message, if the given {@link EventHandler} is not {@code
+   * null}.
+   */
+  private static void debugMessage(
+      @Nullable EventHandler eventHandler, String template, Object... args) {
+    if (eventHandler == null) {
+      return;
+    }
+
+    eventHandler.handle(Event.info("ToolchainResolution: " + String.format(template, args)));
+  }
+
+  /**
    * Returns {@code true} iff all constraints set by the toolchain are present in the {@link
    * PlatformInfo}.
    */
   private static boolean checkConstraints(
-      Iterable<ConstraintValueInfo> toolchainConstraints, PlatformInfo platform) {
+      @Nullable EventHandler eventHandler,
+      Iterable<ConstraintValueInfo> toolchainConstraints,
+      String platformType,
+      PlatformInfo platform) {
 
     for (ConstraintValueInfo constraint : toolchainConstraints) {
       ConstraintValueInfo found = platform.getConstraint(constraint.constraint());
       if (!constraint.equals(found)) {
+        debugMessage(
+            eventHandler,
+            "    Toolchain constraint %s has value %s, "
+                + "which does not match value %s from the %s platform %s",
+            constraint.constraint().label(),
+            constraint.label(),
+            found != null ? found.label() : "<missing>",
+            platformType,
+            platform.label());
         return false;
       }
     }