Improve error messaging for constraints violations.

1) Break up dense lines with clearer pretty-printing.
2) When a violation happens because of a select(), mention
   both the target with the select (as before) *and*
   the dep that the select() chose.
3) Integrate this messaging into --target_environment violations,
   which currently provide no info about the root cause.

Examples:

-------------------------------------
select() + compatible_with violation:
-------------------------------------
Before:
  ERROR: /workspace/testapp/BUILD:41:1: in cc_binary rule //testapp:top: the current command-line flags disqualify all supported environments because of incompatible select() paths:
 environment: //constraints:p removed by: //testapp:midlib (/workspace/testapp/BUILD:28:1)

After:
  ERROR: /workspace/testapp/BUILD:41:1: in cc_binary rule //testapp:top: the current command line flags disqualify all supported environments because of incompatible select() paths:

    environment: //constraints:p
      removed by: //testapp:midlib (/workspace/testapp/BUILD:28:1)
      which has a select() that chooses dep: //testapp:glib
      which lacks: //constraints:p.

-------------------------------------
select() + --target_environment=//constraints:p violation:
-------------------------------------
Before:
  ERROR: This is a restricted-environment build.
   - //testapp:top does not support required environment //constraints:p

After:
  ERROR: This is a restricted-environment build.

  //testapp:top does not support:
    environment: //constraints:p
      removed by: //testapp:midlib (/workspace/testapp/BUILD:28:1)
      which has a select() that chooses dep: //testapp:g
      which lacks: //constraints:p

Fixes: #5795
PiperOrigin-RevId: 207910308

1 files changed, 2 insertions, 1 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java b/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
index ddc1ad6746..09b989f751 100644
--- a/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
+++ b/src/main/java/com/google/devtools/build/lib/analysis/RuleConfiguredTargetBuilder.java
@@ -29,6 +29,7 @@ import com.google.devtools.build.lib.analysis.constraints.ConstraintSemantics;
 import com.google.devtools.build.lib.analysis.constraints.EnvironmentCollection;
 import com.google.devtools.build.lib.analysis.constraints.SupportedEnvironments;
 import com.google.devtools.build.lib.analysis.constraints.SupportedEnvironmentsProvider;
+import com.google.devtools.build.lib.analysis.constraints.SupportedEnvironmentsProvider.RemovedEnvironmentCulprit;
 import com.google.devtools.build.lib.analysis.test.ExecutionInfo;
 import com.google.devtools.build.lib.analysis.test.InstrumentedFilesProvider;
 import com.google.devtools.build.lib.analysis.test.TestActionBuilder;
@@ -183,7 +184,7 @@ public final class RuleConfiguredTargetBuilder {
         constraintSemantics.getSupportedEnvironments(ruleContext);
     if (supportedEnvironments != null) {
       EnvironmentCollection.Builder refinedEnvironments = new EnvironmentCollection.Builder();
-      Map<Label, LabelAndLocation> removedEnvironmentCulprits = new LinkedHashMap<>();
+      Map<Label, RemovedEnvironmentCulprit> removedEnvironmentCulprits = new LinkedHashMap<>();
       constraintSemantics.checkConstraints(ruleContext, supportedEnvironments, refinedEnvironments,
           removedEnvironmentCulprits);
       add(SupportedEnvironmentsProvider.class,