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

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

Differential Revision: https://reviews.llvm.org/D103569

flang/docs/Extensions.md

@@ -93,8 +93,10 @@ accepted if enabled by command-line options.
 * 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)

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

@@ -30,7 +30,7 @@ ENUM_CLASS(LanguageFeature, BackslashEscapes, OldDebugLines,
     EquivalenceNumericWithCharacter, AdditionalIntrinsics, AnonymousParents,
     OldLabelDoEndStatements, LogicalIntegerAssignment, EmptySourceFile,
     ProgramReturn, ImplicitNoneTypeNever, ImplicitNoneTypeAlways,
-    ForwardRefDummyImplicitNone, OpenAccessAppend)
+    ForwardRefDummyImplicitNone, OpenAccessAppend, BOZAsDefaultInteger)
 
 using LanguageFeatures = EnumSet<LanguageFeature, LanguageFeature_enumSize>;
 

flang/lib/Semantics/expression.cpp

@@ -1229,6 +1229,19 @@ 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)}) {
@@ -3334,7 +3347,7 @@ int ArgumentAnalyzer::GetRank(std::size_t i) const {
 }
 
 // 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(