Introduce FlagGroup.expandIfTrue, expandIfFalse

This cl adds support for expand_if_true and expand_if_false messages
to the flag_group, allowing more elegant design of build variables. 
This cl also adds IntegerValue VariableValue subclass.

--
PiperOrigin-RevId: 140849578
MOS_MIGRATED_REVID=140849578

2 files changed, 111 insertions, 4 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainFeatures.java b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainFeatures.java
index 4515aaaec3..5894035668 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainFeatures.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/cpp/CcToolchainFeatures.java
@@ -340,6 +340,8 @@ public class CcToolchainFeatures implements Serializable {
     private final ImmutableSet<String> usedVariables;
     private String iterateOverVariable;
     private final ImmutableSet<String> expandIfAllAvailable;
+    private final String expandIfTrue;
+    private final String expandIfFalse;
 
     /**
      * TODO(b/32655571): Cleanup and get rid of usedVariables field once implicit iteration is not
@@ -375,14 +377,14 @@ public class CcToolchainFeatures implements Serializable {
       this.usedVariables = usedVariables.build();
       this.expandables = expandables.build();
       this.expandIfAllAvailable = ImmutableSet.copyOf(flagGroup.getExpandIfAllAvailableList());
+      this.expandIfTrue = flagGroup.getExpandIfTrue();
+      this.expandIfFalse = flagGroup.getExpandIfFalse();
     }
     
     @Override
     public void expand(Variables variables, final List<String> commandLine) {
-      for (String variable : expandIfAllAvailable) {
-        if (!variables.isAvailable(variable)) {
-          return;
-        }
+      if (!canBeExpanded(variables)) {
+        return;
       }
       if (iterateOverVariable == null) {
         // TODO(b/32655571): Remove branch once implicit iteration is not needed anymore.
@@ -402,6 +404,25 @@ public class CcToolchainFeatures implements Serializable {
       }
     }
 
+    private boolean canBeExpanded(Variables variables) {
+      for (String variable : expandIfAllAvailable) {
+        if (!variables.isAvailable(variable)) {
+          return false;
+        }
+      }
+      if (expandIfTrue != null
+          && variables.isAvailable(expandIfTrue)
+          && !variables.getVariable(expandIfTrue).isTruthy()) {
+        return false;
+      }
+      if (expandIfFalse != null
+          && variables.isAvailable(expandIfFalse)
+          && variables.getVariable(expandIfFalse).isTruthy()) {
+        return false;
+      }
+      return true;
+    }
+
     private Set<String> getUsedVariables() {
       return usedVariables;
     }
@@ -798,6 +819,9 @@ public class CcToolchainFeatures implements Serializable {
        * @param variableName name of the variable value at hand, for better exception message.
        */
       VariableValue getFieldValue(String variableName, String field);
+
+      /** Return true if the variable is truthy */
+      boolean isTruthy();
     }
 
     /** Interface for VariableValue builders */
@@ -905,6 +929,12 @@ public class CcToolchainFeatures implements Serializable {
       }
 
       /** Adds a field to the structure. */
+      public StructureBuilder addField(String name, int value) {
+        fields.put(name, new IntegerValue(value));
+        return this;
+      }
+
+      /** Adds a field to the structure. */
       public StructureBuilder addField(String name, ImmutableList<String> values) {
         fields.put(name, new StringSequence(values));
         return this;
@@ -962,6 +992,11 @@ public class CcToolchainFeatures implements Serializable {
                     + "found sequence",
                 variableName));
       }
+
+      @Override
+      public boolean isTruthy() {
+        return !values.isEmpty();
+      }
     }
 
     /**
@@ -1010,6 +1045,11 @@ public class CcToolchainFeatures implements Serializable {
                     + "found sequence",
                 variableName));
       }
+
+      @Override
+      public boolean isTruthy() {
+        return !Iterables.isEmpty(values);
+      }
     }
 
     /** Sequence of arbitrary VariableValue objects. */
@@ -1049,6 +1089,11 @@ public class CcToolchainFeatures implements Serializable {
                     + "found sequence",
                 variableName));
       }
+
+      @Override
+      public boolean isTruthy() {
+        return values.isEmpty();
+      }
     }
 
     /**
@@ -1095,6 +1140,11 @@ public class CcToolchainFeatures implements Serializable {
       public boolean isSequence() {
         return false;
       }
+
+      @Override
+      public boolean isTruthy() {
+        return !value.isEmpty();
+      }
     }
 
     /**
@@ -1138,6 +1188,59 @@ public class CcToolchainFeatures implements Serializable {
       public boolean isSequence() {
         return false;
       }
+
+      @Override
+      public boolean isTruthy() {
+        return !value.isEmpty();
+      }
+    }
+
+    /**
+     * The leaves in the variable sequence node tree are simple integer values. Note that this
+     * should never live outside of {@code expand}, as the object overhead is prohibitively
+     * expensive.
+     */
+    @Immutable
+    static final class IntegerValue implements VariableValue {
+
+      private final int value;
+
+      public IntegerValue(int value) {
+        this.value = value;
+      }
+
+      @Override
+      public String getStringValue(String variableName) {
+        return Integer.toString(value);
+      }
+
+      @Override
+      public Iterable<? extends VariableValue> getSequenceValue(String variableName) {
+        throw new ExpansionException(
+            String.format(
+                "Invalid toolchain configuration: Cannot expand variable '%s': expected sequence, "
+                    + "found integer",
+                variableName));
+      }
+
+      @Override
+      public VariableValue getFieldValue(String variableName, String field) {
+        throw new ExpansionException(
+            String.format(
+                "Invalid toolchain configuration: Cannot expand variable '%s.%s': variable '%s' is "
+                    + "integer, expected structure",
+                variableName, field, variableName));
+      }
+
+      @Override
+      public boolean isSequence() {
+        return false;
+      }
+
+      @Override
+      public boolean isTruthy() {
+        return value != 0;
+      }
     }
 
     /**
diff --git a/src/main/protobuf/crosstool_config.proto b/src/main/protobuf/crosstool_config.proto
index 51cb5db33b..190c3f546e 100644
--- a/src/main/protobuf/crosstool_config.proto
+++ b/src/main/protobuf/crosstool_config.proto
@@ -100,6 +100,10 @@ message CToolchain {
     optional string iterate_over = 3;
 
     repeated string expand_if_all_available = 4;
+
+    optional string expand_if_true = 5;
+
+    optional string expand_if_false = 6;
   }
 
   // A key/value pair to be added as an environment variable. The value of