cmArchiveWrite: Handle NULL error string (#14882)

If archive_error_string returns NULL, use a placeholder string instead
of crashing.

Source/cmArchiveWrite.cxx

@@ -16,6 +16,13 @@
 #include <cmsys/Directory.hxx>
 #include <cm_libarchive.h>
 
+//----------------------------------------------------------------------------
+static std::string cm_archive_error_string(struct archive* a)
+{
+  const char* e = archive_error_string(a);
+  return e? e : "unknown error";
+}
+
 //----------------------------------------------------------------------------
 class cmArchiveWrite::Entry
 {
@@ -59,7 +66,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
       if(archive_write_set_compression_none(this->Archive) != ARCHIVE_OK)
         {
         this->Error = "archive_write_set_compression_none: ";
-        this->Error += archive_error_string(this->Archive);
+        this->Error += cm_archive_error_string(this->Archive);
         return;
         }
       break;
@@ -67,7 +74,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
       if(archive_write_set_compression_compress(this->Archive) != ARCHIVE_OK)
         {
         this->Error = "archive_write_set_compression_compress: ";
-        this->Error += archive_error_string(this->Archive);
+        this->Error += cm_archive_error_string(this->Archive);
         return;
         }
       break;
@@ -75,7 +82,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
       if(archive_write_set_compression_gzip(this->Archive) != ARCHIVE_OK)
         {
         this->Error = "archive_write_set_compression_gzip: ";
-        this->Error += archive_error_string(this->Archive);
+        this->Error += cm_archive_error_string(this->Archive);
         return;
         }
       break;
@@ -83,7 +90,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
       if(archive_write_set_compression_bzip2(this->Archive) != ARCHIVE_OK)
         {
         this->Error = "archive_write_set_compression_bzip2: ";
-        this->Error += archive_error_string(this->Archive);
+        this->Error += cm_archive_error_string(this->Archive);
         return;
         }
       break;
@@ -91,7 +98,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
       if(archive_write_set_compression_lzma(this->Archive) != ARCHIVE_OK)
         {
         this->Error = "archive_write_set_compression_lzma: ";
-        this->Error += archive_error_string(this->Archive);
+        this->Error += cm_archive_error_string(this->Archive);
         return;
         }
       break;
@@ -99,7 +106,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
       if(archive_write_set_compression_xz(this->Archive) != ARCHIVE_OK)
         {
         this->Error = "archive_write_set_compression_xz: ";
-        this->Error += archive_error_string(this->Archive);
+        this->Error += cm_archive_error_string(this->Archive);
         return;
         }
       break;
@@ -108,7 +115,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
   if (archive_read_disk_set_standard_lookup(this->Disk) != ARCHIVE_OK)
     {
     this->Error = "archive_read_disk_set_standard_lookup: ";
-    this->Error += archive_error_string(this->Archive);
+    this->Error += cm_archive_error_string(this->Archive);
     return;;
     }
 #endif
@@ -118,7 +125,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
       if(archive_write_set_format_zip(this->Archive) != ARCHIVE_OK)
         {
         this->Error = "archive_write_set_format_zip: ";
-        this->Error += archive_error_string(this->Archive);
+        this->Error += cm_archive_error_string(this->Archive);
         return;
         }
       break;
@@ -126,7 +133,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
       if(archive_write_set_format_pax_restricted(this->Archive) != ARCHIVE_OK)
         {
         this->Error = "archive_write_set_format_pax_restricted: ";
-        this->Error += archive_error_string(this->Archive);
+        this->Error += cm_archive_error_string(this->Archive);
         return;
         }
     break;
@@ -136,7 +143,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
   if (archive_write_set_bytes_in_last_block(this->Archive, 1))
     {
     this->Error = "archive_write_set_bytes_in_last_block: ";
-    this->Error += archive_error_string(this->Archive);
+    this->Error += cm_archive_error_string(this->Archive);
     return;
     }
 
@@ -146,7 +153,7 @@ cmArchiveWrite::cmArchiveWrite(std::ostream& os, Compress c, Type t):
        0) != ARCHIVE_OK)
     {
     this->Error = "archive_write_open: ";
-    this->Error += archive_error_string(this->Archive);
+    this->Error += cm_archive_error_string(this->Archive);
     return;
     }
 }
@@ -234,7 +241,7 @@ bool cmArchiveWrite::AddFile(const char* file,
   if(archive_read_disk_entry_from_file(this->Disk, e, -1, 0) != ARCHIVE_OK)
     {
     this->Error = "archive_read_disk_entry_from_file: ";
-    this->Error += archive_error_string(this->Disk);
+    this->Error += cm_archive_error_string(this->Disk);
     return false;
     }
   // Clear acl and xattr fields not useful for distribution.
@@ -244,7 +251,7 @@ bool cmArchiveWrite::AddFile(const char* file,
   if(archive_write_header(this->Archive, e) != ARCHIVE_OK)
     {
     this->Error = "archive_write_header: ";
-    this->Error += archive_error_string(this->Archive);
+    this->Error += cm_archive_error_string(this->Archive);
     return false;
     }
 
@@ -291,7 +298,7 @@ bool cmArchiveWrite::AddData(const char* file, size_t size)
     if(archive_write_data(this->Archive, buffer, nnext) != nnext_s)
       {
       this->Error = "archive_write_data: ";
-      this->Error += archive_error_string(this->Archive);
+      this->Error += cm_archive_error_string(this->Archive);
       return false;
       }
     nleft -= nnext;