[flang] Always check procedure characterizability

When a procedure is defined with a subprogram but never referenced
in a compilation unit, it may not be characterized until lowering,
and any errors in characterization then may crash the compiler.
So always ensure that procedure definitions are characterizable
in declaration checking.

Fixes #91845.

flang/lib/Semantics/check-declarations.cpp

@@ -1357,6 +1357,15 @@ bool CheckHelper::IsResultOkToDiffer(const FunctionResult &result) {
 
 void CheckHelper::CheckSubprogram(
     const Symbol &symbol, const SubprogramDetails &details) {
+  // Evaluate a procedure definition's characteristics to flush out
+  // any errors that analysis might expose, in case this subprogram hasn't
+  // had any calls in this compilation unit that would have validated them.
+  if (!context_.HasError(symbol) && !details.isDummy() &&
+      !details.isInterface() && !details.stmtFunction()) {
+    if (!Procedure::Characterize(symbol, foldingContext_)) {
+      context_.SetError(symbol);
+    }
+  }
   if (const Symbol *iface{FindSeparateModuleSubprogramInterface(&symbol)}) {
     SubprogramMatchHelper{*this}.Check(symbol, *iface);
   }

flang/lib/Semantics/resolve-names.cpp

@@ -5013,8 +5013,7 @@ bool DeclarationVisitor::HasCycle(
     if (procsInCycle.count(*interface) > 0) {
       for (const auto &procInCycle : procsInCycle) {
         Say(procInCycle->name(),
-            "The interface for procedure '%s' is recursively "
-            "defined"_err_en_US,
+            "The interface for procedure '%s' is recursively defined"_err_en_US,
             procInCycle->name());
         context().SetError(*procInCycle);
       }

flang/test/Semantics/entry01.f90

@@ -83,6 +83,7 @@ function ifunc()
   !ERROR: 'ibad1' is already declared in this scoping unit
   entry ibad1() result(ibad1res) ! C1570
   !ERROR: 'ibad2' is already declared in this scoping unit
+  !ERROR: Procedure 'ibad2' is referenced before being sufficiently defined in a context where it must be so
   entry ibad2()
   !ERROR: ENTRY in a function may not have an alternate return dummy argument
   entry ibadalt(*) ! C1573
@@ -91,6 +92,7 @@ function ifunc()
   entry iok()
   !ERROR: Explicit RESULT('iok') of function 'isameres2' cannot have the same name as a distinct ENTRY into the same scope
   entry isameres2() result(iok) ! C1574
+  !ERROR: Procedure 'iok2' is referenced before being sufficiently defined in a context where it must be so
   !ERROR: Explicit RESULT('iok2') of function 'isameres3' cannot have the same name as a distinct ENTRY into the same scope
   entry isameres3() result(iok2) ! C1574
   !ERROR: 'iok2' is already declared in this scoping unit

flang/test/Semantics/resolve102.f90

@@ -4,17 +4,12 @@
 !ERROR: Procedure 'sub' is recursively defined.  Procedures in the cycle: 'sub', 'p2'
 subroutine sub(p2)
   PROCEDURE(sub) :: p2
-
-  call sub()
 end subroutine
 
 subroutine circular
-  !ERROR: Procedure 'p' is recursively defined.  Procedures in the cycle: 'p', 'sub', 'p2'
   procedure(sub) :: p
-
-  call p(sub)
-
   contains
+    !ERROR: Procedure 'sub' is recursively defined.  Procedures in the cycle: 'p', 'sub', 'p2'
     subroutine sub(p2)
       procedure(p) :: p2
     end subroutine
@@ -41,11 +36,10 @@ subroutine sub(p2)
 
 subroutine mutual
   Procedure(sub1) :: p
-
-  Call p(sub)
-
   contains
     !ERROR: Procedure 'sub1' is recursively defined.  Procedures in the cycle: 'p', 'sub1', 'arg'
+    !ERROR: Procedure 'sub1' is recursively defined.  Procedures in the cycle: 'sub1', 'arg', 'sub', 'p2'
+    !ERROR: Procedure 'sub1' is recursively defined.  Procedures in the cycle: 'sub1', 'arg'
     Subroutine sub1(arg)
       procedure(sub1) :: arg
     End Subroutine
@@ -57,15 +51,14 @@ Subroutine sub(p2)
 
 subroutine mutual1
   Procedure(sub1) :: p
-
-  Call p(sub)
-
   contains
     !ERROR: Procedure 'sub1' is recursively defined.  Procedures in the cycle: 'p', 'sub1', 'arg', 'sub', 'p2'
+    !ERROR: Procedure 'sub1' is recursively defined.  Procedures in the cycle: 'sub1', 'arg', 'sub', 'p2'
     Subroutine sub1(arg)
       procedure(sub) :: arg
     End Subroutine
 
+    !ERROR: Procedure 'sub' is recursively defined.  Procedures in the cycle: 'sub1', 'arg', 'sub', 'p2'
     Subroutine sub(p2)
       Procedure(sub1) :: p2
     End Subroutine
@@ -76,8 +69,6 @@ subroutine twoCycle
   !ERROR: The interface for procedure 'p2' is recursively defined
   procedure(p1) p2
   procedure(p2) p1
-  call p1
-  call p2
 end subroutine
 
 subroutine threeCycle
@@ -87,9 +78,6 @@ subroutine threeCycle
   !ERROR: The interface for procedure 'p3' is recursively defined
   procedure(p2) p3
   procedure(p3) p1
-  call p1
-  call p2
-  call p3
 end subroutine
 
 module mutualSpecExprs
@@ -118,4 +106,3 @@ function ifunc(x)
     ifunc = x
   end
 end
-