diff --git a/docs/language.md b/docs/language.md
index 28bdb7a..137300a 100644
--- a/docs/language.md
+++ b/docs/language.md
@@ -58,11 +58,6 @@
 per the above design philosophy, if you need this kind of thing you're probably
 doing it wrong.
 
-The variable `sources` has a special rule: when assigning to it, a list
-of exclusion patterns is applied to it. This is designed to
-automatically filter out some types of files. See `gn help
-set_sources_assignment_filter` and `gn help label_pattern` for more.
-
 The full grammar for language nerds is available in `gn help grammar`.
 
 ### Strings
@@ -471,7 +466,7 @@
 
 Patterns are used to generate the output file names for a given set of
 inputs for custom target types, and to automatically remove files from
-the `sources` variable (see `gn help set_sources_assignment_filter`).
+the list values (see `gn help filter_include` and `gn help filter_exclude`).
 
 They are like simple regular expressions. See `gn help label_pattern`
 for more.
diff --git a/docs/reference.md b/docs/reference.md
index 93cba60..2a987ba 100644
--- a/docs/reference.md
+++ b/docs/reference.md
@@ -57,7 +57,7 @@
     *   [rebase_path: Rebase a file or directory to another location.](#func_rebase_path)
     *   [set_default_toolchain: Sets the default toolchain name.](#func_set_default_toolchain)
     *   [set_defaults: Set default values for a target type.](#func_set_defaults)
-    *   [set_sources_assignment_filter: Set a pattern to filter source files.](#func_set_sources_assignment_filter)
+    *   [set_sources_assignment_filter: Deprecated feature.](#func_set_sources_assignment_filter)
     *   [split_list: Splits a list into N different sub-lists.](#func_split_list)
     *   [string_join: Concatenates a list of strings with a separator.](#func_string_join)
     *   [string_replace: Replaces substring in the given string.](#func_string_replace)
@@ -2424,10 +2424,6 @@
   important because most targets have an implicit configs list, which means it
   wouldn't work at all if it didn't clobber).
 
-  The sources assignment filter (see "gn help set_sources_assignment_filter")
-  is never applied by this function. It's assumed than any desired filtering
-  was already done when sources was set on the from_scope.
-
   If variables_to_not_forward_list is non-empty, then it must contains a list
   of variable names that will not be forwarded. This is mostly useful when
   variable_list_or_star has a value of "*".
@@ -3055,36 +3051,11 @@
     configs -= [ "//tools/mything:settings" ]
   }
 ```
-### <a name="func_set_sources_assignment_filter"></a>**set_sources_assignment_filter**: Set a pattern to filter source files.
+### <a name="func_set_sources_assignment_filter"></a>**set_sources_assignment_filter**: Deprecated feature.
 
 ```
-  The sources assignment filter is a list of patterns that remove files from
-  the list implicitly whenever the "sources" variable is assigned to. This will
-  do nothing for non-lists.
-
-  This is intended to be used to globally filter out files with
-  platform-specific naming schemes when they don't apply, for example you may
-  want to filter out all "*_win.cc" files on non-Windows platforms.
-
-  Typically this will be called once in the master build config script to set
-  up the filter for the current platform. Subsequent calls will overwrite the
-  previous values.
-
-  If you want to bypass the filter and add a file even if it might be filtered
-  out, call set_sources_assignment_filter([]) to clear the list of filters.
-  This will apply until the current scope exits.
-
-  See "gn help file_pattern" for more information on file pattern.
-```
-
-#### **Sources assignment example**
-
-```
-  # Filter out all _win files.
-  set_sources_assignment_filter([ "*_win.cc", "*_win.h" ])
-  sources = [ "a.cc", "b_win.cc" ]
-  print(sources)
-  # Will print [ "a.cc" ]. b_win one was filtered out.
+  This feature is deprecated. It will be removed once all usages have been
+  removed. Only supports a single argument that needs to be an empty list.
 ```
 ### <a name="func_split_list"></a>**split_list**: Splits a list into N different sub-lists.
 
@@ -7078,10 +7049,6 @@
 
     mylist = []
     mylist = otherlist
-
-  When assigning to a list named 'sources' using '=' or '+=', list items may be
-  automatically filtered out. See "gn help set_sources_assignment_filter" for
-  more.
 ```
 
 #### **Scopes**
diff --git a/misc/emacs/gn-mode.el b/misc/emacs/gn-mode.el
index d7bf4bb..dc92c9b 100644
--- a/misc/emacs/gn-mode.el
+++ b/misc/emacs/gn-mode.el
@@ -71,9 +71,8 @@
     "forward_variables_from" "get_label_info" "get_path_info"
     "get_target_outputs" "getenv" "import" "not_needed" "print"
     "process_file_template" "read_file" "rebase_path" "set_default_toolchain"
-    "set_defaults" "set_sources_assignment_filter" "split_list" "string_join"
-    "string_split" "template" "tool" "toolchain" "propagates_configs"
-    "write_file"))
+    "set_defaults" "split_list" "string_join" "string_split" "template" "tool"
+    "toolchain" "propagates_configs" "write_file"))
 
 (defvar gn-font-lock-predefined-var-keywords
   '("current_cpu" "current_os" "current_toolchain" "default_toolchain"
diff --git a/misc/tm/GN.tmLanguage b/misc/tm/GN.tmLanguage
index 5f07e21..8be5f56 100644
--- a/misc/tm/GN.tmLanguage
+++ b/misc/tm/GN.tmLanguage
@@ -73,7 +73,7 @@
       <key>comment</key>
       <string>functions</string>
       <key>match</key>
-      <string>\b(?:assert|config|declare_args|defined|exec_script|foreach|get_label_info|get_path_info|get_target_outputs|getenv|import|print|process_file_template|read_file|rebase_path|set_default_toolchain|set_defaults|set_sources_assignment_filter|split_list|string_join|string_split|template|tool|toolchain|toolchain_args|propagates_configs|write_file)\b</string>
+      <string>\b(?:assert|config|declare_args|defined|exec_script|foreach|get_label_info|get_path_info|get_target_outputs|getenv|import|print|process_file_template|read_file|rebase_path|set_default_toolchain|set_defaults|split_list|string_join|string_split|template|tool|toolchain|toolchain_args|propagates_configs|write_file)\b</string>
       <key>name</key>
       <string>entity.name.function.gn</string>
     </dict>
diff --git a/misc/vim/syntax/gn.vim b/misc/vim/syntax/gn.vim
index 550f39c..454aacc 100644
--- a/misc/vim/syntax/gn.vim
+++ b/misc/vim/syntax/gn.vim
@@ -37,9 +37,8 @@
 syn keyword     gnFunctions get_target_outputs getenv import print
 syn keyword     gnFunctions process_file_template propagates_configs read_file
 syn keyword     gnFunctions rebase_path set_default_toolchain set_defaults
-syn keyword     gnFunctions set_sources_assignment_filter split_list string_join
-syn keyword     gnFunctions string_split template tool toolchain toolchain_args
-syn keyword     gnFunctions write_file
+syn keyword     gnFunctions split_list string_join string_split template tool
+syn keyword     gnFunctions toolchain toolchain_args write_file
 hi def link     gnFunctions         Macro
 
 " Variables
diff --git a/src/gn/function_forward_variables_from.cc b/src/gn/function_forward_variables_from.cc
index 8cee386..ba392e1 100644
--- a/src/gn/function_forward_variables_from.cc
+++ b/src/gn/function_forward_variables_from.cc
@@ -108,10 +108,6 @@
   important because most targets have an implicit configs list, which means it
   wouldn't work at all if it didn't clobber).
 
-  The sources assignment filter (see "gn help set_sources_assignment_filter")
-  is never applied by this function. It's assumed than any desired filtering
-  was already done when sources was set on the from_scope.
-
   If variables_to_not_forward_list is non-empty, then it must contains a list
   of variable names that will not be forwarded. This is mostly useful when
   variable_list_or_star has a value of "*".
diff --git a/src/gn/functions.cc b/src/gn/functions.cc
index 314173b..e627e2a 100644
--- a/src/gn/functions.cc
+++ b/src/gn/functions.cc
@@ -810,35 +810,12 @@
 
 const char kSetSourcesAssignmentFilter[] = "set_sources_assignment_filter";
 const char kSetSourcesAssignmentFilter_HelpShort[] =
-    "set_sources_assignment_filter: Set a pattern to filter source files.";
+    "set_sources_assignment_filter: Deprecated feature.";
 const char kSetSourcesAssignmentFilter_Help[] =
-    R"(set_sources_assignment_filter: Set a pattern to filter source files.
+    R"(set_sources_assignment_filter: Deprecated feature.
 
-  The sources assignment filter is a list of patterns that remove files from
-  the list implicitly whenever the "sources" variable is assigned to. This will
-  do nothing for non-lists.
-
-  This is intended to be used to globally filter out files with
-  platform-specific naming schemes when they don't apply, for example you may
-  want to filter out all "*_win.cc" files on non-Windows platforms.
-
-  Typically this will be called once in the master build config script to set
-  up the filter for the current platform. Subsequent calls will overwrite the
-  previous values.
-
-  If you want to bypass the filter and add a file even if it might be filtered
-  out, call set_sources_assignment_filter([]) to clear the list of filters.
-  This will apply until the current scope exits.
-
-  See "gn help file_pattern" for more information on file pattern.
-
-Sources assignment example
-
-  # Filter out all _win files.
-  set_sources_assignment_filter([ "*_win.cc", "*_win.h" ])
-  sources = [ "a.cc", "b_win.cc" ]
-  print(sources)
-  # Will print [ "a.cc" ]. b_win one was filtered out.
+  This feature is deprecated. It will be removed once all usages have been
+  removed. Only supports a single argument that needs to be an empty list.
 )";
 
 Value RunSetSourcesAssignmentFilter(Scope* scope,
@@ -847,12 +824,19 @@
                                     Err* err) {
   if (args.size() != 1) {
     *err = Err(function, "set_sources_assignment_filter takes one argument.");
-  } else {
-    std::unique_ptr<PatternList> f = std::make_unique<PatternList>();
-    f->SetFromValue(args[0], err);
-    if (!err->has_error())
-      scope->set_sources_assignment_filter(std::move(f));
+    return Value();
   }
+
+  if (!args[0].VerifyTypeIs(Value::LIST, err)) {
+    return Value();
+  }
+
+  if (!args[0].list_value().empty()) {
+    *err = Err(function,
+               "set_sources_assignment_filter argument must be an empty list.");
+    return Value();
+  }
+
   return Value();
 }
 
diff --git a/src/gn/operators.cc b/src/gn/operators.cc
index 3c55a90..7c04dd3 100644
--- a/src/gn/operators.cc
+++ b/src/gn/operators.cc
@@ -16,8 +16,6 @@
 
 namespace {
 
-const char kSourcesName[] = "sources";
-
 // Helper class used for assignment operations: =, +=, and -= to generalize
 // writing to various types of destinations.
 class ValueDestination {
@@ -45,10 +43,6 @@
   // assumption that it will be modified in-place.
   Value* GetExistingMutableValueIfExists(const ParseNode* origin);
 
-  // Returns the sources assignment filter if it exists for the current
-  // scope and it should be applied to this assignment. Otherwise returns null.
-  const PatternList* GetAssignmentFilter(const Scope* exec_scope) const;
-
   // Returns a pointer to the value that was set.
   Value* SetValue(Value value, const ParseNode* set_node);
 
@@ -179,19 +173,6 @@
   return nullptr;
 }
 
-const PatternList* ValueDestination::GetAssignmentFilter(
-    const Scope* exec_scope) const {
-  if (type_ != SCOPE)
-    return nullptr;  // Destination can't be named, so no sources filtering.
-  if (name_token_->value() != kSourcesName)
-    return nullptr;  // Destination not named "sources".
-
-  const PatternList* filter = exec_scope->GetSourcesAssignmentFilter();
-  if (!filter || filter->is_empty())
-    return nullptr;  // No filter or empty filter, don't need to do anything.
-  return filter;
-}
-
 Value* ValueDestination::SetValue(Value value, const ParseNode* set_node) {
   if (type_ == SCOPE) {
     return scope_->SetValue(name_token_->value(), std::move(value), set_node);
@@ -346,17 +327,7 @@
     }
   }
 
-  Value* written_value = dest->SetValue(std::move(right), op_node->right());
-
-  // Optionally apply the assignment filter in-place.
-  const PatternList* filter = dest->GetAssignmentFilter(exec_scope);
-  if (filter && written_value->type() == Value::LIST) {
-    std::vector<Value>& list_value = written_value->list_value();
-    auto first_deleted = std::remove_if(
-        list_value.begin(), list_value.end(),
-        [filter](const Value& v) { return filter->MatchesValue(v); });
-    list_value.erase(first_deleted, list_value.end());
-  }
+  dest->SetValue(std::move(right), op_node->right());
   return Value();
 }
 
@@ -501,21 +472,9 @@
   } else if (mutable_dest->type() == Value::LIST) {
     // List concat.
     if (right.type() == Value::LIST) {
-      // Note: don't reserve() the dest vector here since that actually hurts
-      // the allocation pattern when the build script is doing multiple small
-      // additions.
-      const PatternList* filter = dest->GetAssignmentFilter(exec_scope);
-      if (filter) {
-        // Filtered list concat.
-        for (Value& value : right.list_value()) {
-          if (!filter->MatchesValue(value))
-            mutable_dest->list_value().push_back(std::move(value));
-        }
-      } else {
-        // Normal list concat. This is a destructive move.
-        for (Value& value : right.list_value())
-          mutable_dest->list_value().push_back(std::move(value));
-      }
+      // Normal list concat. This is a destructive move.
+      for (Value& value : right.list_value())
+        mutable_dest->list_value().push_back(std::move(value));
     } else {
       *err = Err(op_node->op(), "Incompatible types to add.",
                  "To append a single item to a list do \"foo += [ bar ]\".");
diff --git a/src/gn/operators_unittest.cc b/src/gn/operators_unittest.cc
index 3c39ae2..415596c 100644
--- a/src/gn/operators_unittest.cc
+++ b/src/gn/operators_unittest.cc
@@ -109,11 +109,6 @@
   TestBinaryOpNode node(Token::PLUS_EQUALS, "+=");
   node.SetLeftToIdentifier(sources);
 
-  // Set up the filter on the scope to remove everything ending with "rm"
-  std::unique_ptr<PatternList> pattern_list = std::make_unique<PatternList>();
-  pattern_list->Append(Pattern("*rm"));
-  setup.scope()->set_sources_assignment_filter(std::move(pattern_list));
-
   // Append an integer.
   node.SetRightToListOfValue(Value(nullptr, static_cast<int64_t>(5)));
   node.Execute(setup.scope(), &err);
@@ -125,14 +120,8 @@
   node.Execute(setup.scope(), &err);
   EXPECT_FALSE(err.has_error());
 
-  // Append a string that does match the pattern, it should be a no-op.
-  const char string2[] = "foo-rm";
-  node.SetRightToListOfValue(Value(nullptr, string2));
-  node.Execute(setup.scope(), &err);
-  EXPECT_FALSE(err.has_error());
-
   // Append a list with the two strings from above.
-  node.SetRightToListOfValue(Value(nullptr, string1), Value(nullptr, string2));
+  node.SetRightToListOfValue(Value(nullptr, string1));
   node.Execute(setup.scope(), &err);
   EXPECT_FALSE(err.has_error());
 
diff --git a/src/gn/parser.cc b/src/gn/parser.cc
index 833e590..b8919ff 100644
--- a/src/gn/parser.cc
+++ b/src/gn/parser.cc
@@ -179,10 +179,6 @@
     mylist = []
     mylist = otherlist
 
-  When assigning to a list named 'sources' using '=' or '+=', list items may be
-  automatically filtered out. See "gn help set_sources_assignment_filter" for
-  more.
-
 Scopes
 
   All execution happens in the context of a scope which holds the current state
diff --git a/src/gn/scope.cc b/src/gn/scope.cc
index a220c8e..a1cf179 100644
--- a/src/gn/scope.cc
+++ b/src/gn/scope.cc
@@ -379,23 +379,6 @@
                                      "<SHOULDN'T HAPPEN>", err);
   }
 
-  // Sources assignment filter.
-  if (sources_assignment_filter_) {
-    if (!options.clobber_existing) {
-      if (dest->GetSourcesAssignmentFilter()) {
-        // Sources assignment filter present in both the source and the dest.
-        std::string desc_string(desc_for_err);
-        *err = Err(node_for_err, "Assignment filter collision.",
-                   "The " + desc_string +
-                       " contains a sources_assignment_filter "
-                       "which\nwould clobber the one in your current scope.");
-        return false;
-      }
-    }
-    dest->sources_assignment_filter_ =
-        std::make_unique<PatternList>(*sources_assignment_filter_);
-  }
-
   // Templates.
   for (const auto& pair : templates_) {
     const std::string& current_name = pair.first;
@@ -483,14 +466,6 @@
   return nullptr;
 }
 
-const PatternList* Scope::GetSourcesAssignmentFilter() const {
-  if (sources_assignment_filter_)
-    return sources_assignment_filter_.get();
-  if (containing())
-    return containing()->GetSourcesAssignmentFilter();
-  return nullptr;
-}
-
 void Scope::SetProcessingBuildConfig() {
   DCHECK((mode_flags_ & kProcessingBuildConfigFlag) == 0);
   mode_flags_ |= kProcessingBuildConfigFlag;
diff --git a/src/gn/scope.h b/src/gn/scope.h
index e800621..4621db5 100644
--- a/src/gn/scope.h
+++ b/src/gn/scope.h
@@ -255,12 +255,6 @@
   // been set.
   const Scope* GetTargetDefaults(const std::string& target_type) const;
 
-  // Filter to apply when the sources variable is assigned. May return NULL.
-  const PatternList* GetSourcesAssignmentFilter() const;
-  void set_sources_assignment_filter(std::unique_ptr<PatternList> f) {
-    sources_assignment_filter_ = std::move(f);
-  }
-
   // Indicates if we're currently processing the build configuration file.
   // This is true when processing the config file for any toolchain.
   //
@@ -370,10 +364,6 @@
   using NamedScopeMap = std::unordered_map<std::string, std::unique_ptr<Scope>>;
   NamedScopeMap target_defaults_;
 
-  // Null indicates not set and that we should fallback to the containing
-  // scope's filter.
-  std::unique_ptr<PatternList> sources_assignment_filter_;
-
   // Owning pointers, must be deleted.
   using TemplateMap = std::map<std::string, scoped_refptr<const Template>>;
   TemplateMap templates_;