diff --git a/debuginfo-tests/dexter/Commands.md b/debuginfo-tests/dexter/Commands.md
--- a/debuginfo-tests/dexter/Commands.md
+++ b/debuginfo-tests/dexter/Commands.md
@@ -9,6 +9,7 @@
 * [DexLimitSteps](Commands.md#DexLimitSteps)
 * [DexLabel](Commands.md#DexLabel)
 * [DexWatch](Commands.md#DexWatch)
+* [DexDeclareFile](Commands.md#DexDeclareFile)
 
 ---
 ## DexExpectProgramState
@@ -231,6 +232,23 @@
 ### Heuristic
 This command does not contribute to the heuristic score.
 
+----
+## DexDeclareFile
+    DexDeclareFile(declared_file)
+
+    Args:
+        name (str): A declared file path for which all subsequent commands
+          will have their path attribute set too.
+
+### Description
+Set the path attribute of all commands from this point in the test onwards.
+The new path holds until the end of the test file or until a new DexDeclareFile
+command is encountered. Used in conjunction with .dex files, DexDeclareFile can
+be used to write your dexter commands in a separate test file avoiding inlined
+Dexter commands mixed with test source.
+
+### Heuristic
+This command does not contribute to the heuristic score.
 
 ---
 ## DexWatch
diff --git a/debuginfo-tests/dexter/d.diff b/debuginfo-tests/dexter/d.diff
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/d.diff
@@ -0,0 +1,463 @@
+diff --git a/debuginfo-tests/dexter/Commands.md b/debuginfo-tests/dexter/Commands.md
+index 5de685906c01..da14b8d59ba7 100644
+--- a/debuginfo-tests/dexter/Commands.md
++++ b/debuginfo-tests/dexter/Commands.md
+@@ -9,6 +9,7 @@
+ * [DexLimitSteps](Commands.md#DexLimitSteps)
+ * [DexLabel](Commands.md#DexLabel)
+ * [DexWatch](Commands.md#DexWatch)
++* [DexDeclareFile](Commands.md#DexDeclareFile)
+ 
+ ---
+ ## DexExpectProgramState
+@@ -231,6 +232,23 @@ arithmetic operators to get offsets from labels:
+ ### Heuristic
+ This command does not contribute to the heuristic score.
+ 
++----
++## DexDeclareFile
++    DexDeclareFile(declared_file)
++
++    Args:
++        name (str): A declared file path for which all subsequent commands
++          will have their path attribute set too.
++
++### Description
++Set the path attribute of all commands from this point in the test onwards.
++The new path holds until the end of the test file or until a new DexDeclareFile
++command is encountered. Used in conjunction with .dex files, DexDeclareFile can
++be used to write your dexter commands in a separate test file avoiding inlined
++Dexter commands mixed with test source.
++
++### Heuristic
++This command does not contribute to the heuristic score.
+ 
+ ---
+ ## DexWatch
+diff --git a/debuginfo-tests/dexter/dex/command/ParseCommand.py b/debuginfo-tests/dexter/dex/command/ParseCommand.py
+index c9908ef4b399..81e5c6c117f0 100644
+--- a/debuginfo-tests/dexter/dex/command/ParseCommand.py
++++ b/debuginfo-tests/dexter/dex/command/ParseCommand.py
+@@ -12,12 +12,13 @@ Python code being embedded within DExTer commands.
+ import os
+ import unittest
+ from copy import copy
+-
++from pathlib import PurePath
+ from collections import defaultdict, OrderedDict
+ 
+ from dex.utils.Exceptions import CommandParseError
+ 
+ from dex.command.CommandBase import CommandBase
++from dex.command.commands.DexDeclareFile import DexDeclareFile
+ from dex.command.commands.DexExpectProgramState import DexExpectProgramState
+ from dex.command.commands.DexExpectStepKind import DexExpectStepKind
+ from dex.command.commands.DexExpectStepOrder import DexExpectStepOrder
+@@ -37,6 +38,7 @@ def _get_valid_commands():
+         { name (str): command (class) }
+     """
+     return {
++      DexDeclareFile.get_name() : DexDeclareFile,
+       DexExpectProgramState.get_name() : DexExpectProgramState,
+       DexExpectStepKind.get_name() : DexExpectStepKind,
+       DexExpectStepOrder.get_name() : DexExpectStepOrder,
+@@ -209,6 +211,8 @@ def add_line_label(labels, label, cmd_path, cmd_lineno):
+ 
+ def _find_all_commands_in_file(path, file_lines, valid_commands):
+     labels = {} # dict of {name: line}.
++    cmd_path = path
++    declared_files = set()
+     commands = defaultdict(dict)
+     paren_balance = 0
+     region_start = TextPoint(0, 0)
+@@ -253,7 +257,7 @@ def _find_all_commands_in_file(path, file_lines, valid_commands):
+                     valid_commands[command_name],
+                     labels,
+                     raw_text,
+-                    path,
++                    cmd_path,
+                     cmd_point.get_lineno(),
+                 )
+             except SyntaxError as e:
+@@ -271,6 +275,14 @@ def _find_all_commands_in_file(path, file_lines, valid_commands):
+             else:
+                 if type(command) is DexLabel:
+                     add_line_label(labels, command, path, cmd_point.get_lineno())
++                elif type(command) is DexDeclareFile:
++                    cmd_path = command.declared_file
++                    if not os.path.isabs(cmd_path):
++                        source_dir = os.path.dirname(path)
++                        cmd_path = os.path.join(source_dir, cmd_path)
++                    # TODO: keep stored paths as PurePaths for 'longer'.
++                    cmd_path = str(PurePath(cmd_path))
++                    declared_files.add(cmd_path)
+                 assert (path, cmd_point) not in commands[command_name], (
+                     command_name, commands[command_name])
+                 commands[command_name][path, cmd_point] = command
+@@ -281,32 +293,34 @@ def _find_all_commands_in_file(path, file_lines, valid_commands):
+         err_point.char += len(command_name)
+         msg = "Unbalanced parenthesis starting here"
+         raise format_parse_err(msg, path, file_lines, err_point)
+-    return dict(commands)
++    return dict(commands), declared_files
+ 
+-def _find_all_commands(source_files):
++def _find_all_commands(test_files):
+     commands = defaultdict(dict)
+     valid_commands = _get_valid_commands()
+-    for source_file in source_files:
+-        with open(source_file) as fp:
++    new_source_files = set()
++    for test_file in test_files:
++        with open(test_file) as fp:
+             lines = fp.readlines()
+-        file_commands = _find_all_commands_in_file(source_file, lines,
+-                                                   valid_commands)
++        file_commands, declared_files = _find_all_commands_in_file(test_file,
++                                                  lines, valid_commands)
+         for command_name in file_commands:
+             commands[command_name].update(file_commands[command_name])
++        new_source_files |= declared_files
+ 
+-    return dict(commands)
++    return dict(commands), new_source_files
+ 
+-def get_command_infos(source_files):
++def get_command_infos(test_files):
+   with Timer('parsing commands'):
+       try:
+-          commands = _find_all_commands(source_files)
++          commands, new_source_files = _find_all_commands(test_files)
+           command_infos = OrderedDict()
+           for command_type in commands:
+               for command in commands[command_type].values():
+                   if command_type not in command_infos:
+                       command_infos[command_type] = []
+                   command_infos[command_type].append(command)
+-          return OrderedDict(command_infos)
++          return OrderedDict(command_infos), new_source_files
+       except CommandParseError as e:
+           msg = 'parser error: <d>{}({}):</> {}\n{}\n{}\n'.format(
+                 e.filename, e.lineno, e.info, e.src, e.caret)
+@@ -344,7 +358,8 @@ class TestParseCommand(unittest.TestCase):
+         Returns:
+             { cmd_name: { (path, line): command_obj } }
+         """
+-        return _find_all_commands_in_file(__file__, lines, self.valid_commands)
++        cmds, declared_files = _find_all_commands_in_file(__file__, lines, self.valid_commands)
++        return cmds
+ 
+ 
+     def _find_all_mock_values_in_lines(self, lines):
+diff --git a/debuginfo-tests/dexter/dex/command/commands/DexDeclareFile.py b/debuginfo-tests/dexter/dex/command/commands/DexDeclareFile.py
+new file mode 100644
+index 000000000000..c40c854575d9
+--- /dev/null
++++ b/debuginfo-tests/dexter/dex/command/commands/DexDeclareFile.py
+@@ -0,0 +1,31 @@
++# DExTer : Debugging Experience Tester
++# ~~~~~~   ~         ~~         ~   ~~
++#
++# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
++# See https://llvm.org/LICENSE.txt for license information.
++# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
++"""Commmand sets the path for all following commands to 'declared_file'.
++"""
++
++from pathlib import PurePath
++
++from dex.command.CommandBase import CommandBase
++
++
++class DexDeclareFile(CommandBase):
++    def __init__(self, declared_file):
++
++        if not isinstance(declared_file, str):
++            raise TypeError('invalid argument type')
++
++        # Use PurePath to create a cannonical platform path.
++        # TODO: keep paths as PurePath objects for 'longer'
++        self.declared_file = str(PurePath(declared_file))
++        super(DexDeclareFile, self).__init__()
++
++    @staticmethod
++    def get_name():
++        return __class__.__name__
++
++    def eval(self):
++        return self.declared_file
+diff --git a/debuginfo-tests/dexter/dex/tools/TestToolBase.py b/debuginfo-tests/dexter/dex/tools/TestToolBase.py
+index a2d8a90c005e..cfea497124b5 100644
+--- a/debuginfo-tests/dexter/dex/tools/TestToolBase.py
++++ b/debuginfo-tests/dexter/dex/tools/TestToolBase.py
+@@ -100,26 +100,38 @@ class TestToolBase(ToolBase):
+         options.executable = os.path.join(
+             self.context.working_directory.path, 'tmp.exe')
+ 
++        # Test files contain dexter commands.
++        options.test_files = []
++        # Source files are to be compiled by the builder script and may also
++        # contains dexter commands.
++        options.source_files = []
+         if os.path.isdir(options.test_path):
+-
+             subdirs = sorted([
+                 r for r, _, f in os.walk(options.test_path)
+                 if 'test.cfg' in f
+             ])
+ 
+             for subdir in subdirs:
+-
+-                # TODO: read file extensions from the test.cfg file instead so
+-                # that this isn't just limited to C and C++.
+-                options.source_files = [
+-                    os.path.normcase(os.path.join(subdir, f))
+-                    for f in os.listdir(subdir) if any(
+-                        f.endswith(ext) for ext in ['.c', '.cpp'])
+-                ]
++                for f in os.listdir(subdir):
++                    # TODO: read file extensions from the test.cfg file instead so
++                    # that this isn't just limited to C and C++.
++                    file_path = os.path.normcase(os.path.join(subdir, f))
++                    if f.endswith('.cpp'):
++                        options.source_files.append(file_path)
++                    elif f.endswith('.c'):
++                        options.source_files.append(file_path)
++                    elif f.endswith('.dex'):
++                        options.test_files.append(file_path)
++                # Source files can contain dexter commands too.
++                options.test_files = options.test_files + options.source_files
+ 
+                 self._run_test(self._get_test_name(subdir))
+         else:
+-            options.source_files = [options.test_path]
++            # We're dealing with a direct file path to a test file. If the file is non
++            # .dex, then it must be a source file.
++            if not options.test_path.endswith('.dex'):
++                options.source_files = [options.test_path]
++            options.test_files = [options.test_path]
+             self._run_test(self._get_test_name(options.test_path))
+ 
+         return self._handle_results()
+diff --git a/debuginfo-tests/dexter/dex/tools/clang_opt_bisect/Tool.py b/debuginfo-tests/dexter/dex/tools/clang_opt_bisect/Tool.py
+index 6e936bd98a3c..c910d9c537ca 100644
+--- a/debuginfo-tests/dexter/dex/tools/clang_opt_bisect/Tool.py
++++ b/debuginfo-tests/dexter/dex/tools/clang_opt_bisect/Tool.py
+@@ -92,8 +92,9 @@ class Tool(TestToolBase):
+             executable_path=self.context.options.executable,
+             source_paths=self.context.options.source_files,
+             dexter_version=self.context.version)
+-        step_collection.commands = get_command_infos(
+-            self.context.options.source_files)
++        step_collection.commands, new_source_files = get_command_infos(
++            self.context.options.test_files)
++        self.context.options.source_files.extend(list(new_source_files))
+         debugger_controller = DefaultController(self.context, step_collection)
+         return debugger_controller
+ 
+diff --git a/debuginfo-tests/dexter/dex/tools/test/Tool.py b/debuginfo-tests/dexter/dex/tools/test/Tool.py
+index 43191fd44bd5..2d3ddce8f7b6 100644
+--- a/debuginfo-tests/dexter/dex/tools/test/Tool.py
++++ b/debuginfo-tests/dexter/dex/tools/test/Tool.py
+@@ -138,8 +138,10 @@ class Tool(TestToolBase):
+             source_paths=self.context.options.source_files,
+             dexter_version=self.context.version)
+ 
+-        step_collection.commands = get_command_infos(
+-            self.context.options.source_files)
++        step_collection.commands, new_source_files = get_command_infos(
++            self.context.options.test_files)
++
++        self.context.options.source_files.extend(list(new_source_files))
+ 
+         if 'DexLimitSteps' in step_collection.commands:
+             debugger_controller = ConditionalController(self.context, step_collection)
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/penalty/dex_declare_file.cpp b/debuginfo-tests/dexter/feature_tests/commands/penalty/dex_declare_file.cpp
+new file mode 100644
+index 000000000000..7860ffd5dda4
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/penalty/dex_declare_file.cpp
+@@ -0,0 +1,17 @@
++// Purpose:
++//    Check that \DexDeclareFile causes a DexExpectWatchValue's to generate a
++//    missing value penalty when the declared path is incorrect.
++//
++// UNSUPPORTED: system-darwin
++//
++//
++// RUN: not %dexter_regression_test -- %s | FileCheck %s
++// CHECK: dex_declare_file.cpp
++
++int main() {
++  int result = 0;
++  return result; //DexLabel('return')
++}
++
++// DexDeclareFile('this_file_does_not_exist.cpp')
++// DexExpectWatchValue('result', 0, on_line='return')
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/commands.dex b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/commands.dex
+new file mode 100644
+index 000000000000..bbad7db943bf
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/commands.dex
+@@ -0,0 +1,2 @@
++DexDeclareFile('test.cpp')
++DexExpectWatchValue('result', 0, on_line=14)
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/lit.local.cfg.py b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/lit.local.cfg.py
+new file mode 100644
+index 000000000000..159c376beedb
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/lit.local.cfg.py
+@@ -0,0 +1 @@
++config.suffixes = ['.cpp']
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cfg b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cfg
+new file mode 100644
+index 000000000000..e69de29bb2d1
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cpp b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cpp
+new file mode 100644
+index 000000000000..5f1d50efe8d0
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cpp
+@@ -0,0 +1,15 @@
++// Purpose:
++//    Check that \DexDeclareFile changes the path of all succeeding commands
++//    to the file path it declares. Also check that dexter correctly accepts
++//    files with .dex extensions.
++//
++// UNSUPPORTED: system-darwin
++//
++//
++// RUN: %dexter_regression_test -- %S | FileCheck %s
++// CHECK: dex_and_source
++
++int main() {
++  int result = 0;
++  return result;
++}
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/commands.dex b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/commands.dex
+new file mode 100644
+index 000000000000..1aec2f8f3b64
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/commands.dex
+@@ -0,0 +1,18 @@
++# Purpose:
++#    Check that \DexDeclareFile's file declaration can reference source files
++#    in a precompiled binary.
++#
++# UNSUPPORTED: system-darwin
++#
++# RUN: %clang %S/test.cpp -O0 -g -o %t
++# RUN: %dexter_regression_test --binary %t %s | FileCheck %s
++# CHECK: commands.dex
++#
++# test.cpp
++# 1. int main() {
++# 2.   int result = 0;
++# 3.   return result;
++# 4. }
++
++DexDeclareFile('test.cpp')
++DexExpectWatchValue('result', 0, on_line=3)
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/lit.local.cfg.py b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/lit.local.cfg.py
+new file mode 100644
+index 000000000000..e65498f23dde
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/lit.local.cfg.py
+@@ -0,0 +1 @@
++config.suffixes = ['.dex']
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/test.cpp b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/test.cpp
+new file mode 100644
+index 000000000000..4d3cc5846e66
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/test.cpp
+@@ -0,0 +1,4 @@
++int main() {
++  int result = 0;
++  return result;
++}
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/dex_commands/commands.dex b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/dex_commands/commands.dex
+new file mode 100644
+index 000000000000..964c770d3325
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/dex_commands/commands.dex
+@@ -0,0 +1,19 @@
++# Purpose:
++#    Check that \DexDeclareFile's file declaration can reference source files
++#    not included in the test directory
++#
++# UNSUPPORTED: system-darwin
++#
++# RUN: %clang %S/../source/test.cpp -O0 -g -o %t
++# RUN: %dexter_regression_test --binary %t %s | FileCheck %s
++# RUN: rm %t
++# CHECK: commands.dex
++#
++# test.cpp
++# 1. int main() {
++# 2.   int result = 0;
++# 3.   return result;
++# 4. }
++
++DexDeclareFile('../source/test.cpp')
++DexExpectWatchValue('result', 0, on_line=3)
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/lit.local.cfg.py b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/lit.local.cfg.py
+new file mode 100644
+index 000000000000..e65498f23dde
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/lit.local.cfg.py
+@@ -0,0 +1 @@
++config.suffixes = ['.dex']
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/source/test.cpp b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/source/test.cpp
+new file mode 100644
+index 000000000000..4d3cc5846e66
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/source/test.cpp
+@@ -0,0 +1,4 @@
++int main() {
++  int result = 0;
++  return result;
++}
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/lit.local.cfg.py b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/lit.local.cfg.py
+new file mode 100644
+index 000000000000..e65498f23dde
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/lit.local.cfg.py
+@@ -0,0 +1 @@
++config.suffixes = ['.dex']
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/source/test file.cpp b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/source/test file.cpp
+new file mode 100644
+index 000000000000..f6dcd82e93e7
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/source/test file.cpp	
+@@ -0,0 +1,4 @@
++int main(const int argc, const char * argv[]) {
++  int result = argc;
++  return result;
++}
+\ No newline at end of file
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.cfg b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.cfg
+new file mode 100644
+index 000000000000..e69de29bb2d1
+diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.dex b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.dex
+new file mode 100644
+index 000000000000..d9c9b80044b6
+--- /dev/null
++++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.dex
+@@ -0,0 +1,17 @@
++# Purpose:
++#    Check that non-canonical paths resolve correctly on Windows.
++#
++# REQUIRES: system-windows
++#
++# RUN: %clang "%S/source/test file.cpp" -O0 -g -o %t
++# RUN: %dexter_regression_test --binary %t %s | FileCheck %s
++# CHECK: test.dex
++#
++# ./source/test file.cpp
++# 1 int main(const int argc, const char * argv[]) {
++# 2 int result = argc;
++# 3 return result;
++# 4 }
++
++DexDeclareFile('./sOuRce\\test filE.cpp')
++DexExpectWatchValue('result', 1, on_line=3)
diff --git a/debuginfo-tests/dexter/dex/command/ParseCommand.py b/debuginfo-tests/dexter/dex/command/ParseCommand.py
--- a/debuginfo-tests/dexter/dex/command/ParseCommand.py
+++ b/debuginfo-tests/dexter/dex/command/ParseCommand.py
@@ -12,12 +12,13 @@
 import os
 import unittest
 from copy import copy
-
+from pathlib import PurePath
 from collections import defaultdict, OrderedDict
 
 from dex.utils.Exceptions import CommandParseError
 
 from dex.command.CommandBase import CommandBase
+from dex.command.commands.DexDeclareFile import DexDeclareFile
 from dex.command.commands.DexExpectProgramState import DexExpectProgramState
 from dex.command.commands.DexExpectStepKind import DexExpectStepKind
 from dex.command.commands.DexExpectStepOrder import DexExpectStepOrder
@@ -37,6 +38,7 @@
         { name (str): command (class) }
     """
     return {
+      DexDeclareFile.get_name() : DexDeclareFile,
       DexExpectProgramState.get_name() : DexExpectProgramState,
       DexExpectStepKind.get_name() : DexExpectStepKind,
       DexExpectStepOrder.get_name() : DexExpectStepOrder,
@@ -209,6 +211,8 @@
 
 def _find_all_commands_in_file(path, file_lines, valid_commands):
     labels = {} # dict of {name: line}.
+    cmd_path = path
+    declared_files = set()
     commands = defaultdict(dict)
     paren_balance = 0
     region_start = TextPoint(0, 0)
@@ -253,7 +257,7 @@
                     valid_commands[command_name],
                     labels,
                     raw_text,
-                    path,
+                    cmd_path,
                     cmd_point.get_lineno(),
                 )
             except SyntaxError as e:
@@ -271,6 +275,14 @@
             else:
                 if type(command) is DexLabel:
                     add_line_label(labels, command, path, cmd_point.get_lineno())
+                elif type(command) is DexDeclareFile:
+                    cmd_path = command.declared_file
+                    if not os.path.isabs(cmd_path):
+                        source_dir = os.path.dirname(path)
+                        cmd_path = os.path.join(source_dir, cmd_path)
+                    # TODO: keep stored paths as PurePaths for 'longer'.
+                    cmd_path = str(PurePath(cmd_path))
+                    declared_files.add(cmd_path)
                 assert (path, cmd_point) not in commands[command_name], (
                     command_name, commands[command_name])
                 commands[command_name][path, cmd_point] = command
@@ -281,32 +293,34 @@
         err_point.char += len(command_name)
         msg = "Unbalanced parenthesis starting here"
         raise format_parse_err(msg, path, file_lines, err_point)
-    return dict(commands)
+    return dict(commands), declared_files
 
-def _find_all_commands(source_files):
+def _find_all_commands(test_files):
     commands = defaultdict(dict)
     valid_commands = _get_valid_commands()
-    for source_file in source_files:
-        with open(source_file) as fp:
+    new_source_files = set()
+    for test_file in test_files:
+        with open(test_file) as fp:
             lines = fp.readlines()
-        file_commands = _find_all_commands_in_file(source_file, lines,
-                                                   valid_commands)
+        file_commands, declared_files = _find_all_commands_in_file(test_file,
+                                                  lines, valid_commands)
         for command_name in file_commands:
             commands[command_name].update(file_commands[command_name])
+        new_source_files |= declared_files
 
-    return dict(commands)
+    return dict(commands), new_source_files
 
-def get_command_infos(source_files):
+def get_command_infos(test_files):
   with Timer('parsing commands'):
       try:
-          commands = _find_all_commands(source_files)
+          commands, new_source_files = _find_all_commands(test_files)
           command_infos = OrderedDict()
           for command_type in commands:
               for command in commands[command_type].values():
                   if command_type not in command_infos:
                       command_infos[command_type] = []
                   command_infos[command_type].append(command)
-          return OrderedDict(command_infos)
+          return OrderedDict(command_infos), new_source_files
       except CommandParseError as e:
           msg = 'parser error: <d>{}({}):</> {}\n{}\n{}\n'.format(
                 e.filename, e.lineno, e.info, e.src, e.caret)
@@ -344,7 +358,8 @@
         Returns:
             { cmd_name: { (path, line): command_obj } }
         """
-        return _find_all_commands_in_file(__file__, lines, self.valid_commands)
+        cmds, declared_files = _find_all_commands_in_file(__file__, lines, self.valid_commands)
+        return cmds
 
 
     def _find_all_mock_values_in_lines(self, lines):
diff --git a/debuginfo-tests/dexter/dex/command/commands/DexDeclareFile.py b/debuginfo-tests/dexter/dex/command/commands/DexDeclareFile.py
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/dex/command/commands/DexDeclareFile.py
@@ -0,0 +1,31 @@
+# DExTer : Debugging Experience Tester
+# ~~~~~~   ~         ~~         ~   ~~
+#
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+"""Commmand sets the path for all following commands to 'declared_file'.
+"""
+
+from pathlib import PurePath
+
+from dex.command.CommandBase import CommandBase
+
+
+class DexDeclareFile(CommandBase):
+    def __init__(self, declared_file):
+
+        if not isinstance(declared_file, str):
+            raise TypeError('invalid argument type')
+
+        # Use PurePath to create a cannonical platform path.
+        # TODO: keep paths as PurePath objects for 'longer'
+        self.declared_file = str(PurePath(declared_file))
+        super(DexDeclareFile, self).__init__()
+
+    @staticmethod
+    def get_name():
+        return __class__.__name__
+
+    def eval(self):
+        return self.declared_file
diff --git a/debuginfo-tests/dexter/dex/tools/TestToolBase.py b/debuginfo-tests/dexter/dex/tools/TestToolBase.py
--- a/debuginfo-tests/dexter/dex/tools/TestToolBase.py
+++ b/debuginfo-tests/dexter/dex/tools/TestToolBase.py
@@ -100,26 +100,38 @@
         options.executable = os.path.join(
             self.context.working_directory.path, 'tmp.exe')
 
+        # Test files contain dexter commands.
+        options.test_files = []
+        # Source files are to be compiled by the builder script and may also
+        # contains dexter commands.
+        options.source_files = []
         if os.path.isdir(options.test_path):
-
             subdirs = sorted([
                 r for r, _, f in os.walk(options.test_path)
                 if 'test.cfg' in f
             ])
 
             for subdir in subdirs:
-
-                # TODO: read file extensions from the test.cfg file instead so
-                # that this isn't just limited to C and C++.
-                options.source_files = [
-                    os.path.normcase(os.path.join(subdir, f))
-                    for f in os.listdir(subdir) if any(
-                        f.endswith(ext) for ext in ['.c', '.cpp'])
-                ]
+                for f in os.listdir(subdir):
+                    # TODO: read file extensions from the test.cfg file instead so
+                    # that this isn't just limited to C and C++.
+                    file_path = os.path.normcase(os.path.join(subdir, f))
+                    if f.endswith('.cpp'):
+                        options.source_files.append(file_path)
+                    elif f.endswith('.c'):
+                        options.source_files.append(file_path)
+                    elif f.endswith('.dex'):
+                        options.test_files.append(file_path)
+                # Source files can contain dexter commands too.
+                options.test_files = options.test_files + options.source_files
 
                 self._run_test(self._get_test_name(subdir))
         else:
-            options.source_files = [options.test_path]
+            # We're dealing with a direct file path to a test file. If the file is non
+            # .dex, then it must be a source file.
+            if not options.test_path.endswith('.dex'):
+                options.source_files = [options.test_path]
+            options.test_files = [options.test_path]
             self._run_test(self._get_test_name(options.test_path))
 
         return self._handle_results()
diff --git a/debuginfo-tests/dexter/dex/tools/clang_opt_bisect/Tool.py b/debuginfo-tests/dexter/dex/tools/clang_opt_bisect/Tool.py
--- a/debuginfo-tests/dexter/dex/tools/clang_opt_bisect/Tool.py
+++ b/debuginfo-tests/dexter/dex/tools/clang_opt_bisect/Tool.py
@@ -92,8 +92,9 @@
             executable_path=self.context.options.executable,
             source_paths=self.context.options.source_files,
             dexter_version=self.context.version)
-        step_collection.commands = get_command_infos(
-            self.context.options.source_files)
+        step_collection.commands, new_source_files = get_command_infos(
+            self.context.options.test_files)
+        self.context.options.source_files.extend(list(new_source_files))
         debugger_controller = DefaultController(self.context, step_collection)
         return debugger_controller
 
diff --git a/debuginfo-tests/dexter/dex/tools/test/Tool.py b/debuginfo-tests/dexter/dex/tools/test/Tool.py
--- a/debuginfo-tests/dexter/dex/tools/test/Tool.py
+++ b/debuginfo-tests/dexter/dex/tools/test/Tool.py
@@ -138,8 +138,10 @@
             source_paths=self.context.options.source_files,
             dexter_version=self.context.version)
 
-        step_collection.commands = get_command_infos(
-            self.context.options.source_files)
+        step_collection.commands, new_source_files = get_command_infos(
+            self.context.options.test_files)
+
+        self.context.options.source_files.extend(list(new_source_files))
 
         if 'DexLimitSteps' in step_collection.commands:
             debugger_controller = ConditionalController(self.context, step_collection)
diff --git a/debuginfo-tests/dexter/feature_tests/commands/penalty/dex_declare_file.cpp b/debuginfo-tests/dexter/feature_tests/commands/penalty/dex_declare_file.cpp
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/penalty/dex_declare_file.cpp
@@ -0,0 +1,17 @@
+// Purpose:
+//    Check that \DexDeclareFile causes a DexExpectWatchValue's to generate a
+//    missing value penalty when the declared path is incorrect.
+//
+// UNSUPPORTED: system-darwin
+//
+//
+// RUN: not %dexter_regression_test -- %s | FileCheck %s
+// CHECK: dex_declare_file.cpp
+
+int main() {
+  int result = 0;
+  return result; //DexLabel('return')
+}
+
+// DexDeclareFile('this_file_does_not_exist.cpp')
+// DexExpectWatchValue('result', 0, on_line='return')
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/commands.dex b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/commands.dex
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/commands.dex
@@ -0,0 +1,2 @@
+DexDeclareFile('test.cpp')
+DexExpectWatchValue('result', 0, on_line=14)
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/lit.local.cfg.py b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/lit.local.cfg.py
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/lit.local.cfg.py
@@ -0,0 +1 @@
+config.suffixes = ['.cpp']
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cfg b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cfg
new file mode 100644
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cpp b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cpp
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/dex_and_source/test.cpp
@@ -0,0 +1,15 @@
+// Purpose:
+//    Check that \DexDeclareFile changes the path of all succeeding commands
+//    to the file path it declares. Also check that dexter correctly accepts
+//    files with .dex extensions.
+//
+// UNSUPPORTED: system-darwin
+//
+//
+// RUN: %dexter_regression_test -- %S | FileCheck %s
+// CHECK: dex_and_source
+
+int main() {
+  int result = 0;
+  return result;
+}
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/commands.dex b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/commands.dex
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/commands.dex
@@ -0,0 +1,18 @@
+# Purpose:
+#    Check that \DexDeclareFile's file declaration can reference source files
+#    in a precompiled binary.
+#
+# UNSUPPORTED: system-darwin
+#
+# RUN: %clang %S/test.cpp -O0 -g -o %t
+# RUN: %dexter_regression_test --binary %t %s | FileCheck %s
+# CHECK: commands.dex
+#
+# test.cpp
+# 1. int main() {
+# 2.   int result = 0;
+# 3.   return result;
+# 4. }
+
+DexDeclareFile('test.cpp')
+DexExpectWatchValue('result', 0, on_line=3)
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/lit.local.cfg.py b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/lit.local.cfg.py
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/lit.local.cfg.py
@@ -0,0 +1 @@
+config.suffixes = ['.dex']
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/test.cpp b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/test.cpp
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary/test.cpp
@@ -0,0 +1,4 @@
+int main() {
+  int result = 0;
+  return result;
+}
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/dex_commands/commands.dex b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/dex_commands/commands.dex
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/dex_commands/commands.dex
@@ -0,0 +1,19 @@
+# Purpose:
+#    Check that \DexDeclareFile's file declaration can reference source files
+#    not included in the test directory
+#
+# UNSUPPORTED: system-darwin
+#
+# RUN: %clang %S/../source/test.cpp -O0 -g -o %t
+# RUN: %dexter_regression_test --binary %t %s | FileCheck %s
+# RUN: rm %t
+# CHECK: commands.dex
+#
+# test.cpp
+# 1. int main() {
+# 2.   int result = 0;
+# 3.   return result;
+# 4. }
+
+DexDeclareFile('../source/test.cpp')
+DexExpectWatchValue('result', 0, on_line=3)
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/lit.local.cfg.py b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/lit.local.cfg.py
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/lit.local.cfg.py
@@ -0,0 +1 @@
+config.suffixes = ['.dex']
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/source/test.cpp b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/source/test.cpp
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/precompiled_binary_different_dir/source/test.cpp
@@ -0,0 +1,4 @@
+int main() {
+  int result = 0;
+  return result;
+}
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/lit.local.cfg.py b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/lit.local.cfg.py
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/lit.local.cfg.py
@@ -0,0 +1 @@
+config.suffixes = ['.dex']
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/source/test file.cpp b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/source/test file.cpp
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/source/test file.cpp	
@@ -0,0 +1,4 @@
+int main(const int argc, const char * argv[]) {
+  int result = argc;
+  return result;
+}
\ No newline at end of file
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.cfg b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.cfg
new file mode 100644
diff --git a/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.dex b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.dex
new file mode 100644
--- /dev/null
+++ b/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_file/windows_noncanonical_path/test.dex
@@ -0,0 +1,17 @@
+# Purpose:
+#    Check that non-canonical paths resolve correctly on Windows.
+#
+# REQUIRES: system-windows
+#
+# RUN: %clang "%S/source/test file.cpp" -O0 -g -o %t
+# RUN: %dexter_regression_test --binary %t %s | FileCheck %s
+# CHECK: test.dex
+#
+# ./source/test file.cpp
+# 1 int main(const int argc, const char * argv[]) {
+# 2 int result = argc;
+# 3 return result;
+# 4 }
+
+DexDeclareFile('./sOuRce\\test filE.cpp')
+DexExpectWatchValue('result', 1, on_line=3)