Delete output files if this is a failed run.

Otherwise, the fail will stop a Makefile from progressing, but if you
immediately run the build again, Make will think the output files are up to
date, since they are newer (albeit incomplete/incorrect).

FossilOrigin-Name: e38c08d9cdeb0476ac1a77cd3f29f547a8205835
diff --git a/tool/lemon.c b/tool/lemon.c
index 122ab97..4a3bfa1 100644
--- a/tool/lemon.c
+++ b/tool/lemon.c
@@ -34,6 +34,24 @@
 #define MAXRHS 1000
 #endif
 
+static const char **made_files = NULL;
+static int made_files_count = 0;
+static int successful_exit = 0;
+static void LemonAtExit(void)
+{
+    /* if we failed, delete (most) files we made, to unconfuse build tools. */
+    int i;
+    for (i = 0; i < made_files_count; i++) {
+        if (!successful_exit) {
+            remove(made_files[i]);
+        }
+        free((void *) made_files[i]);
+    }
+    free(made_files);
+    made_files_count = 0;
+    made_files = NULL;
+}
+
 static char *msort(char*,char**,int(*)(const char*,const char*));
 
 /*
@@ -1470,6 +1488,8 @@
   int exitcode;
   struct lemon lem;
 
+  atexit(LemonAtExit);
+
   OptInit(argv,options,stderr);
   if( version ){
      printf("Lemon version 1.0\n");
@@ -1576,6 +1596,7 @@
 
   /* return 0 on success, 1 on failure. */
   exitcode = ((lem.errorcnt > 0) || (lem.nconflict != lem.nexpected)) ? 1 : 0;
+  successful_exit = (exitcode == 0);
   exit(exitcode);
   return (exitcode);
 }
@@ -2831,6 +2852,24 @@
     lemp->errorcnt++;
     return 0;
   }
+
+  /* Add files we create to a list, so we can delete them if we fail. This
+  ** is to keep makefiles from getting confused. We don't include .out files,
+  ** though: this is debug information, and you don't want it deleted if there
+  ** was an error you need to track down.
+  */
+  if(( *mode=='w' ) && (strcmp(suffix, ".out") != 0)){
+    const char **ptr = (const char **)
+        realloc(made_files, sizeof (const char **) * (made_files_count + 1));
+    char *fname = strdup(lemp->outname);
+    if ((ptr == NULL) || (fname == NULL)) {
+        free(ptr);
+        free(fname);
+        memory_error();
+    }
+    made_files = ptr;
+    made_files[made_files_count++] = fname;
+  }
   return fp;
 }