From 5d7c0028195bfd04cf488808cc494dbb113e3125 Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Sun, 13 Feb 2022 16:33:43 -0600
Subject: [PATCH] Fix bug causing some #undefs to be ignored when using a sym
 file.

This would occur if the macro had already been saved in the sym file and the #undef occurred before a subsequent #include that was also recorded in the sym file. The solution is simply to terminate sym file generation if an #undef of an already-saved macro is encountered.

Here is an example showing the problem:

test.c:
#include "test1.h"
#undef x
#include "test2.h"

int main(void) {
#ifdef x
        return x;
#else
        return y;
#endif
}

test1.h:
#define x 27

test2.h:
#define y 6
---
 Header.pas  | 2 +-
 Scanner.pas | 2 ++
 cc.notes    | 2 ++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/Header.pas b/Header.pas
index b80a242..9c3e27d 100644
--- a/Header.pas
+++ b/Header.pas
@@ -18,7 +18,7 @@ uses CCommon, MM, Scanner, Symbol, CGI;
 {$segment 'SCANNER'}
 
 const
-   symFileVersion = 21;                 {version number of .sym file format}
+   symFileVersion = 22;                 {version number of .sym file format}
 
 var
    inhibitHeader: boolean;		{should .sym includes be blocked?}
diff --git a/Scanner.pas b/Scanner.pas
index 3bd09db..bab212a 100644
--- a/Scanner.pas
+++ b/Scanner.pas
@@ -2943,6 +2943,8 @@ var
                   bPtr^ := mPtr^.next
                else
                   lastPtr^.next := mPtr^.next;
+               if mPtr^.saved then
+                  TermHeader;
                end; {else}
             goto 1;
             end; {if}
diff --git a/cc.notes b/cc.notes
index 5260f3b..d16ad0d 100644
--- a/cc.notes
+++ b/cc.notes
@@ -1775,6 +1775,8 @@ int foo(int[42]);
 
 179. Macro definitions or header search paths specified via the cc= portion of the command line could be saved in the .sym file and applied to subsequent compilations, even if they were no longer specified on the command line.
 
+180. Certain #undef directives might be ignored when using a .sym file.
+
 -- Bugs from C 2.1.0 that have been fixed -----------------------------------
 
 1.  In some situations, fread() reread the first 1K or so of the file.