Warn when we map unrecognized library files to -l flags.

This is rather an odd feature and I think we should notify users if they
are relying on it.  Honestly I doubt many are.

See #14689 for an example of how confusing it can be when it goes wrong.

Also, make sure we strip off the full suffix in the case of `.so.1.2.3`
suffixes.

Author: sbc100

emcc.py

@@ -892,6 +892,17 @@ def get_file_suffix(filename):
   return ''
 
 
+def get_library_basename(filename):
+  """Similar to get_file_suffix this strips of all numeric suffixes and then
+  then final non-numeric one.  For example for 'libz.so.1.2.8' returns 'libz'"""
+  filename = os.path.basename(filename)
+  while filename:
+    filename, suffix = os.path.splitext(filename)
+    # Keep stipping suffixes until we strip a non-numeric one.
+    if not suffix[1:].isdigit():
+      return filename
+
+
 def get_secondary_target(target, ext):
   # Depending on the output format emscripten creates zero or more secondary
   # output files (e.g. the .wasm file when creating JS output, or the
@@ -1236,8 +1247,10 @@ def phase_setup(options, state, newargs, settings_map):
         # For shared libraries that are neither bitcode nor wasm, assuming its local native
         # library and attempt to find a library by the same name in our own library path.
         # TODO(sbc): Do we really need this feature?  See test_other.py:test_local_link
-        libname = strip_prefix(unsuffixed_basename(arg), 'lib')
-        add_link_flag(state, i, '-l' + libname)
+        libname = strip_prefix(get_library_basename(arg), 'lib')
+        flag = '-l' + libname
+        diagnostics.warning('map-unrecognized-libraries', f'unrecognized file type: `{arg}`.  Mapping to `{flag}` and hoping for the best')
+        add_link_flag(state, i, flag)
       else:
         input_files.append((i, arg))
     elif arg.startswith('-L'):

tests/test_other.py

@@ -1226,7 +1226,7 @@ def test_local_link(self):
     ''')
 
     ensure_dir('subdir')
-    create_file('subdir/libfile.so', 'this is not llvm bitcode!')
+    create_file('subdir/libfile.so.1.2.3', 'this is not llvm bitcode!')
 
     create_file('libfile.cpp', '''
       #include <stdio.h>
@@ -1236,7 +1236,7 @@ def test_local_link(self):
     ''')
 
     self.run_process([EMXX, 'libfile.cpp', '-shared', '-o', 'libfile.so'], stderr=PIPE)
-    self.run_process([EMXX, 'main.cpp', Path('subdir/libfile.so'), '-L.'])
+    self.run_process([EMXX, 'main.cpp', Path('subdir/libfile.so.1.2.3'), '-L.'])
     self.assertContained('hello from lib', self.run_js('a.out.js'))
 
   def test_identical_basenames(self):

tools/shared.py

@@ -65,6 +65,7 @@
 diagnostics.add_warning('deprecated', shared=True)
 diagnostics.add_warning('version-check')
 diagnostics.add_warning('export-main')
+diagnostics.add_warning('map-unrecognized-libraries')
 diagnostics.add_warning('unused-command-line-argument', shared=True)
 diagnostics.add_warning('pthreads-mem-growth')