h2ph: define all symbols at runtime

Preprocessor directives must be processed strictly in order. `#if` and
`#ifdef` directives can inspect the current state of defined symbols.
That's why it is wrong to translate `#define FOO() ...` to `sub foo() {
... }` since subroutine definitions are processed unconditionally at
compile time, before the rest of the code starts running.

In particular,

    unless(defined(&FOO)) {
        sub FOO () { eval q(1); }
    }

is equivalent to

    # at compile time:
    sub FOO () { eval q(1); }

    # ... later, at runtime:
    unless(defined(&FOO)) {
        # does nothing
    }

Fix this case by always wrapping subroutines in eval '...', which moves
the symbol definition to runtime, regardless of what $t (our indentation
state) is.

Similarly, generate `_h2ph_pre.ph` without the functionally useless
`unless (defined &...) { }` blocks. We don't need runtime definitions
(via eval) here because nothing in this file depends on the dynamic
state of macro definitions. It's all `#define`s, no `#if`s.

Fixes #22109.

Author: mauke

t/lib/h2ph.h

@@ -16,6 +16,15 @@
 #define ERROR(x) fprintf(stderr, "%s\n", x[2][3][0])
 #endif /* ERROR */
 
+/* check for correct order of definitions vs. conditionals */
+#ifdef NOT_DEFINED_HERE()
+    /* handle indented directives */
+    #error "NOT_DEFINED_HERE should not be defined at this point!"
+#endif
+
+/* function-like macro with no parameters, outside of any conditional */
+#define NOT_DEFINED_HERE() 42
+
 #ifndef _H2PH_H_
 #define _H2PH_H_
 

t/lib/h2ph.pht

@@ -2,18 +2,22 @@ require '_h2ph_pre.ph';
 
 no warnings qw(redefine misc);
 
-unless(defined(&SQUARE)) {
-    sub SQUARE {
-	my($x) = @_;
+eval 'sub SQUARE {
+    my($x) = @_;
 	eval q((($x)*($x)));
-    }
-}
+}' unless defined(&SQUARE);
 unless(defined(&ERROR)) {
     eval 'sub ERROR {
         my($x) = @_;
 	    eval q( &fprintf( &stderr, \\"%s\\\\n\\", $x->[2][3][0]));
     }' unless defined(&ERROR);
 }
+if(defined(&NOT_DEFINED_HERE)) {
+    die("NOT_DEFINED_HERE should not be defined at this point!");
+}
+eval 'sub NOT_DEFINED_HERE () {
+    eval q(42);
+}' unless defined(&NOT_DEFINED_HERE);
 unless(defined(&_H2PH_H_)) {
     eval 'sub _H2PH_H_ () {1;}' unless defined(&_H2PH_H_);
     # "$Revision h2ph.h,v 1.0 98/05/04 20:42:14 billy $"

utils/h2ph.PL

@@ -392,7 +392,6 @@ sub EMIT {
 
     $new = reindent($new);
     $args = reindent($args);
-    if ($t ne '') {
     $new =~ s/(['\\])/\\$1/g;   #']);
     if ($opt_h) {
         print OUT $t,
@@ -402,9 +401,6 @@ sub EMIT {
         print OUT $t,
                     "eval 'sub $name $proto\{\n$t    ${args}eval q($new);\n$t}' unless defined(\&$name);\n";
     }
-    } else {
-              print OUT "unless(defined(\&$name)) {\n    sub $name $proto\{\n\t${args}eval q($new);\n    }\n}\n";
-    }
     %curargs = ();
     return;
 }
@@ -774,7 +770,7 @@ sub inc_dirs
 sub build_preamble_if_necessary
 {
     # Increment $VERSION every time this function is modified:
-    my $VERSION     = 4;
+    my $VERSION     = 5;
     my $preamble    = "$Dest_dir/_h2ph_pre.ph";
 
     # Can we skip building the preamble file?
@@ -812,18 +808,16 @@ sub build_preamble_if_necessary
 		my $def = $define{$_};
 		$def =~ s/$arg/\$\{$arg\}/g;
 		print PREAMBLE <<DEFINE;
-unless (defined &$macro) { sub $macro(\$) { my (\$$arg) = \@_; \"$def\" } }
+sub $macro(\$) { my (\$$arg) = \@_; \"$def\" }
 
 DEFINE
 	    } elsif
 		($define{$_} =~ /^([+-]?(\d+)?\.\d+([eE][+-]?\d+)?)[FL]?$/) {
 		# float:
-		print PREAMBLE
-		    "unless (defined &$_) { sub $_() { $1 } }\n\n";
+		print PREAMBLE "sub $_() { $1 }\n\n";
 	    } elsif ($define{$_} =~ /^([+-]?\d+)U?L{0,2}$/i) {
 		# integer:
-		print PREAMBLE
-		    "unless (defined &$_) { sub $_() { $1 } }\n\n";
+		print PREAMBLE "sub $_() { $1 }\n\n";
             } elsif ($define{$_} =~ /^([+-]?0x[\da-f]+)U?L{0,2}$/i) {
                 # hex integer
                 # Special cased, since perl warns on hex integers
@@ -834,21 +828,16 @@ DEFINE
                 # platform-specific definition.
                 my $code = $1;
                 $code = "hex('$code')" if length $code > 10;
-                print PREAMBLE
-                    "unless (defined &$_) { sub $_() { $code } }\n\n";
+                print PREAMBLE "sub $_() { $code }\n\n";
 	    } elsif ($define{$_} =~ /^\w+$/) {
 		my $def = $define{$_};
 		if ($isatype{$def}) {
-		  print PREAMBLE
-		    "unless (defined &$_) { sub $_() { \"$def\" } }\n\n";
+		  print PREAMBLE "sub $_() { \"$def\" }\n\n";
 		} else {
-		  print PREAMBLE
-		    "unless (defined &$_) { sub $_() { &$def } }\n\n";
+		  print PREAMBLE "sub $_() { &$def }\n\n";
 	        }
 	    } else {
-		print PREAMBLE
-		    "unless (defined &$_) { sub $_() { \"",
-		    quotemeta($define{$_}), "\" } }\n\n";
+		print PREAMBLE "sub $_() { \"\Q$define{$_}\E\" }\n\n";
 	    }
 	}
 	print PREAMBLE "\n1;\n";  # avoid 'did not return a true value' when empty