ParseXS: refactor: set XSRETURN_count_* earlier

Previously these two values were set at the end of parsing an XSUB:

    XSRETURN_count_basic
    XSRETURN_count_extra

They represent whether a RETVAL SV will be returned by the XSUB, and
how many extra SVs are returned due to parameters declared as OUTLIST.

This commit sets them earlier, as in particular, the next commit will
need to access XSRETURN_count_basic earlier.

XSRETURN_count_extra is now set right after parsing the XSUB's
declaration, as its value can't change after then.

XSRETURN_count_basic is now set after parsing the output part of the
each body of the XSUB (an XSUB can have a body per CASE). Its value
*aught* to be consistent across all bodies, but it's possible for the
CODE_sets_ST0 hack (which looks for code like like 'ST(0) = ...' in any
CODE: block) to vary across bodies; so this commit also adds a new
warning and test for that.

Author: iabyn

dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS/Node.pm

@@ -204,7 +204,8 @@ BEGIN { $build_subclass->('', # parent
     'seen_SCOPE',
 
     # These three fields indicate how many SVs are returned to the caller,
-    # and so influence the emitting of EXTEND(n) and XSRETURN(n).
+    # and so influence the emitting of 'EXTEND(n)', 'XSRETURN(n)', and
+    # potentially, the value of n in 'ST(n) = ...'.
     #
     # XSRETURN_count_basic is 0 or 1 and indicates whether a basic return
     # value is pushed onto the stack. It is usually directly related to
@@ -365,21 +366,6 @@ sub parse {
         }
     } # end while (@{ $pxs->{line} })
 
-    # Work out how many SVs will be returned
-
-    $self->{XSRETURN_count_basic} =
-           (     $self->{CODE_sets_ST0}
-             or  (    $self->{decl}{return_type}{type} ne "void"
-                  && !$self->{decl}{return_type}{no_output})
-            )
-            ? 1 : 0;
-
-    $self->{XSRETURN_count_extra} =
-                        grep {    defined $_->{in_out}
-                               && $_->{in_out} =~ /OUTLIST$/
-                             }
-                        @{$self->{decl}{params}{kids}};
-
     # If any aliases have been declared, make the main sub name ix 0
     # if not specified.
 
@@ -767,6 +753,14 @@ sub parse {
     $params->parse($pxs, $xsub, $params_text);
     $self->{params} = $params;
 
+    # How many OUTLIST SVs get returned in addition to RETVAL
+    $xsub->{XSRETURN_count_extra} =
+                        grep {    defined $_->{in_out}
+                               && $_->{in_out} =~ /OUTLIST$/
+                             }
+                        @{$self->{params}{kids}};
+
+
     1;
 }
 
@@ -2806,6 +2800,17 @@ sub parse {
             . $ExtUtils::ParseXS::Constants::generic_xsub_keywords_alt,
         );
 
+    # Work out whether a RETVAL SV will be returned. Note that this should
+    # be consistent across CASEs; we warn elsewhere if CODE_sets_ST0 isn't
+    # consistent.
+
+    $xsub->{XSRETURN_count_basic} =
+           (     $xsub->{CODE_sets_ST0}
+             or  (    $xsub->{decl}{return_type}{type} ne "void"
+                  && !$xsub->{decl}{return_type}{no_output})
+            )
+            ? 1 : 0;
+
     1;
 }
 
@@ -3697,10 +3702,15 @@ sub parse {
     # will be used later when deciding how/whether to emit EXTEND(n) and
     # XSRETURN(n).
 
-    $xsub->{CODE_sets_ST0} =
+    my $st0 =
              $code =~ m{  ( \b ST      \s* \( [^;]* = )
                         | ( \b XST_m\w+\s* \(         ) }x;
 
+    $pxs->Warn("Warning: ST(0) isn't consistently set in every CASE's CODE block")
+        if     defined $xsub->{CODE_sets_ST0}
+            && $xsub->{CODE_sets_ST0} ne $st0;
+    $xsub->{CODE_sets_ST0} = $st0;
+
     1;
 }
 

dist/ExtUtils-ParseXS/t/001-basic.t

@@ -3620,6 +3620,21 @@ EOF
             [ 1, 0, qr/\QError: junk at end of function: "    INPUTx:" in /,
                     "expected err" ],
         ],
+        [
+            "CASE: setting ST(0)",
+            [ Q(<<'EOF') ],
+                |void
+                |foo(a)
+                |CASE: X
+                |    CODE:
+                |      ST(0) = 1;
+                |CASE: Y
+                |    CODE:
+                |      blah
+EOF
+            [ 1, 0, qr/\QWarning: ST(0) isn't consistently set in every CASE's CODE block/,
+                    "expected err" ],
+        ],
 
 
     );