Relax restriction around case-when operand (#3376)

The `CASE` expression requires the when-operand to be a `BooleanValue`,
which is too strict. The operand must return a `Boolean` type, but it
can be an `Value`, for example, this should work:

```sql
create table t1(col1 bigint, col2 boolean, primary key(col1));
insert into t1 values (1, true), (2, false);
select col2, coalesce(case when col2 then 42 end, 100) from t1;
true, 42
false, 100
```

This fixes #3374.

Author: hatyo

fdb-relational-core/src/main/java/com/apple/foundationdb/relational/recordlayer/query/visitors/ExpressionVisitor.java

@@ -25,7 +25,6 @@
 import com.apple.foundationdb.record.query.plan.cascades.predicates.CompatibleTypeEvolutionPredicate;
 import com.apple.foundationdb.record.query.plan.cascades.typing.Type;
 import com.apple.foundationdb.record.query.plan.cascades.values.AbstractArrayConstructorValue;
-import com.apple.foundationdb.record.query.plan.cascades.values.BooleanValue;
 import com.apple.foundationdb.record.query.plan.cascades.values.ConditionSelectorValue;
 import com.apple.foundationdb.record.query.plan.cascades.values.ExistsValue;
 import com.apple.foundationdb.record.query.plan.cascades.values.FieldValue;
@@ -311,12 +310,13 @@ public Expression visitScalarFunctionCall(@Nonnull RelationalParser.ScalarFuncti
     @Nonnull
     @Override
     public Expression visitCaseFunctionCall(@Nonnull RelationalParser.CaseFunctionCallContext ctx) {
-        final ImmutableList.Builder<BooleanValue> implications = ImmutableList.builder();
+        final ImmutableList.Builder<Value> implications = ImmutableList.builder();
         final ImmutableList.Builder<Value> pickerValues = ImmutableList.builder();
         for (final var caseAlternative : ctx.caseFuncAlternative()) {
             final var condition = visitFunctionArg(caseAlternative.condition);
+            Assert.thatUnchecked(condition.getDataType().getCode().equals(DataType.Code.BOOLEAN));
             final var consequent = visitFunctionArg(caseAlternative.consequent);
-            implications.add(Assert.castUnchecked(condition.getUnderlying(), BooleanValue.class));
+            implications.add(condition.getUnderlying());
             pickerValues.add(consequent.getUnderlying());
         }
         if (ctx.ELSE() != null) {

yaml-tests/src/test/resources/case-when.yamsql

@@ -21,13 +21,17 @@
 schema_template:
     create type as struct S(S1 bigint, S2 bigint)
     create table A(A1 bigint, A2 bigint, A3 bigint, primary key(A1))
+    create table B(B1 bigint, B2 boolean, primary key(B1))
 ---
 setup:
   steps:
     - query: insert into A values
         (1, 10, 10),
         (2, 11, 20),
         (3, 12, 30);
+    - query: insert into B values
+        (1, true),
+        (2, false);
 ---
 test_block:
   tests:
@@ -37,6 +41,19 @@ test_block:
                   { A1: 2, A2: 11, A3: 20 },
                   { A1: 3, A2: 12, A3: 30 } ]
 ---
+test_block:
+  tests:
+    -
+      - query: select a3, case when a3 > 15 then 'foo' else 'bar' end from A;
+      - result: [ { A3: 10, 'bar' },
+                  { A3: 20, 'foo' },
+                  { A3: 30, 'foo' } ]
+    -
+      - query: select b2, case when b2 then 'foo' else 'bar' end from b;
+      - supported_version: !current_version
+      - result: [ { B2: true, 'foo' },
+                  { B2: false, 'bar' } ]
+---
 setup:
   steps:
     - query: update A set A2 = case when A1 = 1 then 4444 end