cpplint · PNHD · Aug 31, 2026 · Aug 31, 2026 · Sep 18, 2026 · Sep 18, 2026
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
@@ -5,6 +5,7 @@ Changelog
 TBA
 ===
 
+* Allow source files to include headers from the same directory without a directory prefix. (#375)
 * Fixed a whitespace/newline false positive for control conditions containing lambdas. (#410)
 * We now error on relative include paths (``./``, ``../``). (#432)
    * This makes ``#include "./foo.h"`` produce two separate errors: that foo.cpp should include foo.h and that relative paths are not allowed.

diff --git a/cpplint.py b/cpplint.py
@@ -5856,13 +5856,31 @@ def CheckIncludeLine(filename, clean_lines, linenum, include_state, error):
         and IsHeaderExtension(match.group(2))
         and not _third_party_headers_pattern.match(match.group(1))
     ):
-        error(
-            filename,
-            linenum,
-            "build/include_subdir",
-            4,
-            "Include the directory when naming header files",
-        )
+        source_path = os.path.realpath(filename)
+        same_dir_header = os.path.join(os.path.dirname(source_path), match.group(1))
+        if not os.path.isfile(same_dir_header):
+            error(
+                filename,
+                linenum,
+                "build/include_subdir",
+                4,
+                "Include the directory when naming header files",
+            )
+        else:
+            try:
+                is_same_file = os.path.samefile(same_dir_header, filename)
+            except (OSError, ValueError):
+                is_same_file = os.path.normcase(
+                    os.path.normpath(same_dir_header)
+                ) == os.path.normcase(os.path.normpath(source_path))
+            if is_same_file:
+                error(
+                    filename,
+                    linenum,
+                    "build/include_subdir",
+                    4,
+                    "Include the directory when naming header files",
+                )
 
     # we shouldn't include a file more than once. actually, there are a
     # handful of instances where doing so is okay, but in general it's

diff --git a/cpplint_unittest.py b/cpplint_unittest.py
@@ -5824,13 +5824,39 @@ def testBuildHeaderGuardWithRepository(self):
             cpplint._repository = None
             cpplint._root = None
 
-    def testBuildInclude(self):
+    def testBuildInclude(self, tmp_path):
         # Test that include statements have slashes in them.
-        self.TestLint(
+        repo = tmp_path / "repo"
+        repo.mkdir()
+        (repo / ".git").mkdir()
+        root_source = repo / "foo.cc"
+        root_source.write_text("")
+        root_header = repo / "foo.h"
+        root_header.write_text("")
+        source_dir = repo / "src"
+        source_dir.mkdir()
+        nested_source = source_dir / "foo.cc"
+        nested_source.write_text("")
+        same_dir_header = source_dir / "utils.hpp"
+        same_dir_header.write_text("")
+
+        self.TestLanguageRulesCheck(
+            str(root_source),
+            '#include "foo.h"',
+            "",
+        )
+        self.TestLanguageRulesCheck(
+            str(nested_source),
+            '#include "utils.hpp"',
+            "",
+        )
+        self.TestLanguageRulesCheck(
+            str(nested_source),
             '#include "foo.h"',
             "Include the directory when naming header files  [build/include_subdir] [4]",
         )
-        self.TestLint(
+        self.TestLanguageRulesCheck(
+            str(nested_source),
             '#include "bar.hh"',
             "Include the directory when naming header files  [build/include_subdir] [4]",
         )
@@ -5852,6 +5878,75 @@ def testBuildInclude(self):
         self.TestLint('#include "Python.h"', "")
         self.TestLint('#include "lua.h"', "")
 
+    def testBuildIncludeSymlinkPath(self, tmp_path):
+        physical_dir = tmp_path / "physical"
+        (physical_dir / "child").mkdir(parents=True)
+        lexical_dir = tmp_path / "lexical"
+        lexical_dir.mkdir()
+        symlink = lexical_dir / "link"
+        try:
+            symlink.symlink_to(physical_dir / "child", target_is_directory=True)
+        except OSError as error:
+            pytest.skip(f"directory symlinks are unavailable: {error}")
+
+        source = physical_dir / "foo.cc"
+        source.write_text("")
+        source_path = symlink / ".." / source.name
+        try:
+            if not source_path.exists() or not os.path.samefile(source_path, source):
+                pytest.skip("directory symlink paths do not resolve '..' through the target")
+        except OSError as error:
+            pytest.skip(f"directory symlink parent traversal is unavailable: {error}")
+
+        same_dir_header = physical_dir / "utils.hpp"
+        same_dir_header.write_text("")
+        self.TestLanguageRulesCheck(str(source_path), '#include "utils.hpp"', "")
+
+        same_dir_header.unlink()
+        (lexical_dir / "utils.hpp").write_text("")
+        self.TestLanguageRulesCheck(
+            str(source_path),
+            '#include "utils.hpp"',
+            "Include the directory when naming header files  [build/include_subdir] [4]",
+        )
+
+    def testBuildIncludeSymlinkAlias(self, tmp_path):
+        source = tmp_path / "self.h"
+        source.write_text("")
+        expected = "Include the directory when naming header files  [build/include_subdir] [4]"
+
+        symlink = tmp_path / "symlink.h"
+        try:
+            symlink.symlink_to(source)
+        except OSError as error:
+            pytest.skip(f"file symlinks are unavailable: {error}")
+        self.TestLanguageRulesCheck(str(source), '#include "symlink.h"', expected)
+
+    def testBuildIncludeHardlinkAlias(self, tmp_path):
+        source = tmp_path / "self.h"
+        source.write_text("")
+        expected = "Include the directory when naming header files  [build/include_subdir] [4]"
+        hardlink = tmp_path / "hardlink.h"
+        try:
+            os.link(source, hardlink)
+        except OSError as error:
+            pytest.skip(f"hard links are unavailable: {error}")
+        self.TestLanguageRulesCheck(str(source), '#include "hardlink.h"', expected)
+
+    def testBuildIncludeInvalidHeaderPath(self, tmp_path):
+        source = tmp_path / "source.cc"
+        source.write_text("")
+        self.TestLanguageRulesCheck(
+            str(source),
+            '#include "bad\x00.h"',
+            "Include the directory when naming header files  [build/include_subdir] [4]",
+        )
+
+    def testBuildIncludeInvalidNonHeaderPath(self, tmp_path):
+        source = tmp_path / "source.cc"
+        source.write_text("")
+        self.TestLanguageRulesCheck(str(source), '#include "bad\x00.txt"', "")
+
     def testHppInclude(self):
         code = "\n".join(["#include <vector>", "#include <boost/any.hpp>"])
         self.TestLanguageRulesCheck("foo.h", code, "")

diff --git a/samples/codelite-sample/simple.def b/samples/codelite-sample/simple.def
@@ -3,10 +3,9 @@ src/*
 4
 Done processing src/pptable.cpp
 Done processing src/pptable.h
-Total errors found: 675
+Total errors found: 674
 
 src/pptable.cpp:0:  No copyright message found.  You should have a line: "Copyright [year] <Copyright Owner>"  [legal/copyright] [5]
-src/pptable.cpp:1:  Include the directory when naming header files  [build/include_subdir] [4]
 src/pptable.cpp:6:  { should almost always be at the end of the previous line  [whitespace/braces] [4]
 src/pptable.cpp:7:  Tab found; better to use spaces  [whitespace/tab] [1]
 src/pptable.cpp:8:  Tab found; better to use spaces  [whitespace/tab] [1]

diff --git a/samples/vlc-sample/simple.def b/samples/vlc-sample/simple.def
@@ -4,15 +4,14 @@ src/*
 Done processing src/libvlc.c
 Done processing src/libvlc.h
 Done processing src/missing.c
-Total errors found: 600
+Total errors found: 599
 
 src/libvlc.c:40:  Relative paths like . and .. are not allowed.  [build/include] [4]
 src/libvlc.c:41:  Found C system header after other header. Should be: libvlc.h, c system, c++ system, other.  [build/include_order] [4]
 src/libvlc.c:47:  Found C system header after other header. Should be: libvlc.h, c system, c++ system, other.  [build/include_order] [4]
 src/libvlc.c:48:  Found C system header after other header. Should be: libvlc.h, c system, c++ system, other.  [build/include_order] [4]
 src/libvlc.c:49:  Found C system header after other header. Should be: libvlc.h, c system, c++ system, other.  [build/include_order] [4]
 src/libvlc.c:50:  Found C system header after other header. Should be: libvlc.h, c system, c++ system, other.  [build/include_order] [4]
-src/libvlc.c:71:  Include the directory when naming header files  [build/include_subdir] [4]
 src/libvlc.c:75:  Found C system header after other header. Should be: libvlc.h, c system, c++ system, other.  [build/include_order] [4]
 src/libvlc.c:86:  Extra space before [  [whitespace/braces] [5]
 src/libvlc.c:86:  Extra space after ( in function call  [whitespace/parens] [4]