[flang] Accept BOZ in array constructors w/o types

[klausler]

Summary

As a benign extension common to other Fortran compilers,
accept BOZ literals in array constructors w/o explicit
types, treating them as integers.

[PeteSteinfeld]

All builds, tests, and looks good.

flang/docs/Extensions.md

* $ and \ edit descriptors are supported in FORMAT to suppress newline
   output on user prompts.
 * REAL and DOUBLE PRECISION variable and bounds in DO loops
 * Integer literals without explicit kind specifiers that are out of range
   for the default kind of INTEGER are assumed to have the least larger kind
   that can hold them, if one exists.
 * BOZ literals can be used as INTEGER values in contexts where the type is
   unambiguous: the right hand sides of assigments and initializations
   of INTEGER entities, and as actual arguments to a few intrinsic functions
-  (ACHAR, BTEST, CHAR).  But they cannot be used if the type would not
-  be known (e.g., `IAND(X'1',X'2')`).
+  (ACHAR, BTEST, CHAR).  BOZ literals are interpreted as default INTEGER
+  when they appear as the first items of array constructors with no
+  explicit type.  Otherwise, they generally cannot be used if the type would
+  not be known (e.g., `IAND(X'1',X'2')`).
 * BOZ literals can also be used as REAL values in some contexts where the
   type is unambiguous, such as initializations of REAL parameters.
 * EQUIVALENCE of numeric and character sequences (a ubiquitous extension)
 * Values for whole anonymous parent components in structure constructors
   (e.g., `EXTENDEDTYPE(PARENTTYPE(1,2,3))` rather than `EXTENDEDTYPE(1,2,3)`
    or `EXTENDEDTYPE(PARENTTYPE=PARENTTYPE(1,2,3))`).
 * Some intrinsic functions are specified in the standard as requiring the
   same type and kind for their arguments (viz., ATAN with two arguments,

flang/include/flang/Common/Fortran-features.h

ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
     Carriagecontrol, Convert, Dispose, IOListLeadingComma,
     AbbreviatedEditDescriptor, ProgramParentheses, PercentRefAndVal,
     OmitFunctionDummies, CrayPointer, Hollerith, ArithmeticIF, Assign,
     AssignedGOTO, Pause, OpenACC, OpenMP, CruftAfterAmpersand, ClassicCComments,
     AdditionalFormats, BigIntLiterals, RealDoControls,
     EquivalenceNumericWithCharacter, AdditionalIntrinsics, AnonymousParents,
     OldLabelDoEndStatements, LogicalIntegerAssignment, EmptySourceFile,
     ProgramReturn, ImplicitNoneTypeNever, ImplicitNoneTypeAlways,
-    ForwardRefDummyImplicitNone, OpenAccessAppend)
+    ForwardRefDummyImplicitNone, OpenAccessAppend, BOZAsDefaultInteger)
 
 using LanguageFeatures = EnumSet<LanguageFeature, LanguageFeature_enumSize>;
 
 class LanguageFeatureControl {
 public:
   LanguageFeatureControl() {
     // These features must be explicitly enabled by command line options.
     disable_.set(LanguageFeature::OldDebugLines);

flang/lib/Semantics/expression.cpp

private:
   ArrayConstructorValues<SomeType> values_;
   std::uint64_t messageDisplayedSet_{0};
 };
 
 void ArrayConstructorContext::Push(MaybeExpr &&x) {
   if (!x) {
     return;
   }
+  if (!type_) {
+    if (auto *boz{std::get_if<BOZLiteralConstant>(&x->u)}) {
+      // Treat an array constructor of BOZ as if default integer.
+      if (exprAnalyzer_.context().ShouldWarn(
+              common::LanguageFeature::BOZAsDefaultInteger)) {
+        exprAnalyzer_.Say(
+            "BOZ literal in array constructor without explicit type is assumed to be default INTEGER"_en_US);
+      }
+      x = AsGenericExpr(ConvertToKind<TypeCategory::Integer>(
+          exprAnalyzer_.GetDefaultKind(TypeCategory::Integer),
+          std::move(*boz)));
+    }
+  }
   if (auto dyType{x->GetType()}) {
     DynamicTypeWithLength xType{*dyType};
     if (Expr<SomeCharacter> * charExpr{UnwrapExpr<Expr<SomeCharacter>>(*x)}) {
       CHECK(xType.category() == TypeCategory::Character);
       xType.length =
           std::visit([](const auto &kc) { return kc.LEN(); }, charExpr->u);
     }
     if (!type_) {

 std::optional<DynamicType> ArgumentAnalyzer::GetType(std::size_t i) const {
   return i < actuals_.size() ? actuals_[i].value().GetType() : std::nullopt;
 }
 int ArgumentAnalyzer::GetRank(std::size_t i) const {
   return i < actuals_.size() ? actuals_[i].value().Rank() : 0;
 }
 
 // If the argument at index i is a BOZ literal, convert its type to match the
-// otherType.  It it's REAL convert to REAL, otherwise convert to INTEGER.
+// otherType.  If it's REAL convert to REAL, otherwise convert to INTEGER.
 // Note that IBM supports comparing BOZ literals to CHARACTER operands.  That
 // is not currently supported.
 void ArgumentAnalyzer::ConvertBOZ(
     std::size_t i, std::optional<DynamicType> otherType) {
   if (IsBOZLiteral(i)) {
     Expr<SomeType> &&argExpr{MoveExpr(i)};
     auto *boz{std::get_if<BOZLiteralConstant>(&argExpr.u)};
     if (otherType && otherType->category() == TypeCategory::Real) {