Clean repeated entries in PATH after vcvars call

conans/client/tools/win.py

@@ -306,7 +306,7 @@ def vcvars_command(settings, arch=None, compiler_version=None, force=False, vcva
 
 def vcvars_dict(settings, arch=None, compiler_version=None, force=False, filter_known_paths=False,
                 vcvars_ver=None, winsdk_version=None, only_diff=True):
-    known_path_lists = ("INCLUDE", "LIB", "LIBPATH", "PATH")
+    known_path_lists = ("include", "lib", "libpath", "path")
     cmd = vcvars_command(settings, arch=arch,
                          compiler_version=compiler_version, force=force,
                          vcvars_ver=vcvars_ver, winsdk_version=winsdk_version) + " && echo __BEGINS__ && set"
@@ -324,14 +324,17 @@ def vcvars_dict(settings, arch=None, compiler_version=None, force=False, filter_
             continue
         try:
             name_var, value = line.split("=", 1)
-            new_value = value.split(os.pathsep) if name_var in known_path_lists else value
+            new_value = value.split(os.pathsep) if name_var.lower() in known_path_lists else value
             # Return only new vars & changed ones, but only with the changed elements if the var is
             # a list
             if only_diff:
                 old_value = os.environ.get(name_var)
-                # The new value ends with separator and the old value, is a list, get only the
-                # new elements
-                if old_value and value.endswith(os.pathsep + old_value):
+                if name_var.lower() == "path":
+                    old_values_lower = [v.lower() for v in old_value.split(os.pathsep)]
+                    # Clean all repeated entries, not append if the element was already there
+                    new_env[name_var] = [v for v in new_value if v.lower() not in old_values_lower]
+                elif old_value and value.endswith(os.pathsep + old_value):
+                    # The new value ends with separator and the old value, is a list, get only the new elements
                     new_env[name_var] = value[:-(len(old_value) + 1)].split(os.pathsep)
                 elif value != old_value:
                     # Only if the vcvars changed something, we return the variable,
@@ -355,7 +358,6 @@ def relevant_path(path):
 
     return new_env
 
-
 @contextmanager
 def vcvars(*args, **kwargs):
     if platform.system() == "Windows":

conans/test/util/tools_test.py

@@ -710,6 +710,31 @@ def vcvars_echo_test(self):
             self.assertIn("Conan:vcvars already set", str(output))
             self.assertIn("VS140COMNTOOLS=", str(output))
 
+    @unittest.skipUnless(platform.system() == "Windows", "Requires Windows")
+    def vcvars_env_not_duplicated_path_test(self):
+        """vcvars is not looking at the current values of the env vars, with PATH it is a problem because you
+        can already have set some of the vars and accumulate unnecessary entries."""
+        settings = Settings.loads(default_settings_yml)
+        settings.os = "Windows"
+        settings.compiler = "Visual Studio"
+        settings.compiler.version = "15"
+        settings.arch = "x86"
+        settings.arch_build = "x86_64"
+
+        # Set the env with a PATH containing the vcvars paths
+        tmp = tools.vcvars_dict(settings, only_diff=False)
+        tmp = {key.lower(): value for key, value in tmp.items()}
+        with tools.environment_append({"path": tmp["path"]}):
+            previous_path = os.environ["PATH"].split(";")
+            # Duplicate the path, inside the tools.vcvars shouldn't have repeated entries in PATH
+            with tools.vcvars(settings):
+                path = os.environ["PATH"].split(";")
+                values_count = {value: path.count(value) for value in path}
+                for value, counter in values_count.items():
+                    if value and counter > 1 and previous_path.count(value) != counter:
+                        # If the entry was already repeated before calling "tools.vcvars" we keep it
+                        self.fail("The key '%s' has been repeated" % value)
+
     @unittest.skipUnless(platform.system() == "Windows", "Requires Windows")
     def vcvars_amd64_32_cross_building_support_test(self):
         # amd64_x86 crossbuilder