Hi, I cloned the tkdom repo, opened it, and then tried to build it with the following options:

./configure --with-tcl='/usr/local/opt/tcl-tk/lib' --enable-html5

make

gcc -dynamiclib -pipe  -Os -DNDEBUG -Wall -fno-common -I/usr/local/opt/tcl-tk/include -I/usr/local/opt/tcl-tk/include  -L/usr/local/opt/tcl-tk/lib -L/usr/local/opt/tcl-tk/lib -prebind -headerpad_max_install_names -Wl,-search_paths_first  -Wl,-single_module -current_version 0.9.2 -compatibility_version 0.9.2 -o libtdom0.9.2.dylib xmlrole.o xmltok.o xmlparse.o xmlsimple.o dom.o domhtml.o domhtml5.o domjson.o domxpath.o domxslt.o domlock.o tcldom.o nodecmd.o tdominit.o tclexpat.o tclpull.o tdomStubInit.o -L/usr/local/Cellar/gumbo-parser/0.10.1/lib -lgumbo  -L/usr/local/Cellar/tcl-tk/8.6.10/lib -ltclstub8.6
ld: warning: option -prebind is obsolete and being ignored
duplicate symbol '_tdomStubsPtr' in:
    tdominit.o
    tclpull.o
duplicate symbol '_tdomStubsPtr' in:
    tdominit.o
    tdomStubInit.o
ld: 2 duplicate symbols for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [libtdom0.9.2.dylib] Error 1

--disable stubs

--enable-html5

MacOS Catalina
10.15.5

Apple clang version 11.0.3 (clang-1103.0.32.62)
Target: x86_64-apple-darwin19.5.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

tcl-tk: stable 8.6.10

Thanks for reporting. Unfortunately I haven't an OS X box at hand atm to reproduce the problem.

Is this about trunk or the state of the latest release (tag tdom-0-9-1)?

Both trunk and the lastest release build for me on linux with gcc and clang (I've clang version 3.8.1-24 - is this in fact that much older than yours as the version nummers suggest?) without problems (or even warnings, at least for trunk) and it builds for me on windows (w/ mingw).

From the reported error msg and looking at the sources nothing obvious strikes me.

I'm in need for your help, to track this down.

Hi de!

I confirm this issue on my box (but I don't know why this would be specific to macOS, or why you don't see the symbol duplicates elsewhere).

Between these two commits 

     fossil diff --from d4bb0eb147b1671a --to d41caf001d9d4d2a

in tdomDecls.h you dropped  "extern" for
   
   -extern const TdomStubs *tdomStubsPtr;
   +const TdomStubs *tdomStubsPtr;

This leads to the classic duplicate definition in the compilation units including tdomDecls.h during linking (tdominit.c and tdomStubLib.c, for example). 

The below fixes this for me (and aligns the definition in tdominit.c).

-------%<------- 
Index: generic/tdomDecls.h
==================================================================
--- generic/tdomDecls.h
+++ generic/tdomDecls.h
@@ -85,11 +85,11 @@
     int (*xML_GetIdAttributeIndex) (XML_Parser parser); /* 15 */
     domNode * (*tcldom_getNodeFromName) (Tcl_Interp *interp, char *nodeName, char **errMsg); /* 16 */
     domDocument * (*tcldom_getDocumentFromName) (Tcl_Interp *interp, char *docName, char **errMsg); /* 17 */
 } TdomStubs;
 
-const TdomStubs *tdomStubsPtr;
+EXTERN const TdomStubs *tdomStubsPtr;
 
 #ifdef __cplusplus
 }
 #endif
 

Index: generic/tdominit.c
==================================================================
--- generic/tdominit.c
+++ generic/tdominit.c
@@ -39,11 +39,11 @@
 #include <dom.h>
 #include <tdom.h>
 #include <tcldom.h>
 #include <tclpull.h>
 
-extern TdomStubs tdomStubs;
+const TdomStubs *tdomStubsPtr;
 
 /*
  *----------------------------------------------------------------------------
  *
  * Tdom_Init --
@@ -93,11 +93,11 @@
     Tcl_CreateObjCommand(interp, "tdom::pullparser", tDOM_PullParserCmd, NULL, NULL );    
 #endif
     
 #ifdef USE_TCL_STUBS
     Tcl_PkgProvideEx(interp, PACKAGE_NAME, PACKAGE_VERSION, 
-                     (ClientData) &tdomStubs);
+                     (ClientData) tdomStubsPtr);
 #else
     Tcl_PkgProvide(interp, PACKAGE_NAME, PACKAGE_VERSION);
 #endif
 
     return TCL_OK;
-------%<------- 

HTH, mr_calvin

Reverted my fix and applied the better one provided by mr_calvin. Thanks.