[libc++] Documentation for _LIBCPP_REMOVE_TRANSITIVE_INCLUDES

[martinlicht]

Closes #130486

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[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Martin Licht (martinlicht)

Changes

Add _LIBCPP_REMOVE_TRANSITIVE_INCLUDES to the list of configuration macros

---

Full diff: https://github.com/llvm/llvm-project/pull/130560.diff

1 Files Affected:

• (modified) libcxx/docs/UserDocumentation.rst (+18)

diff --git a/libcxx/docs/UserDocumentation.rst b/libcxx/docs/UserDocumentation.rst
index 2c1bc1373659c..b55651a62ec5e 100644
--- a/libcxx/docs/UserDocumentation.rst
+++ b/libcxx/docs/UserDocumentation.rst
@@ -128,6 +128,24 @@ enable or disable extended libc++ behavior.
   replacement scenarios from working, e.g. replacing `operator new` and
   expecting a non-replaced `operator new[]` to call the replaced `operator new`.
 
+**_LIBCPP_REMOVE_TRANSITIVE_INCLUDES**:
+  When this macro is defined, the standard library headers will adhere to a
+  stricter policy regarding the (transitive) inclusion of other standard library
+  headers, only guaranteeing to provide those definitions explicitly mandated by
+  the standard. Please notice that defining this macro might break any existing
+  codebase that implicitly relies on standard headers providing any definitions
+  not explicitly required by the standard.
+
+  The primary motivation for this configuration macro is to improve compilation
+  times. In most standard library implementations, header files include more
+  definitions than officially required because the implementation details give rise
+  to internal dependencies. The common practice is to have the standard headers
+  internally include other standard headers, but this generally results in
+  increased compilation overhead. This configuration option attempts to mitigate
+  this problem by avoiding such unnecessary inclusions. In addition, compiling
+  a codebase with this macro may improve maintainability by identifying
+  missing standard header inclusions.
+
 **_LIBCPP_DISABLE_DEPRECATION_WARNINGS**:
   This macro disables warnings when using deprecated components. For example,
   using `std::auto_ptr` when compiling in C++11 mode will normally trigger a

[frederick-vs-ja]

You can link your pull request to this issue using GitHub's close/fix/resolve syntax (in the PR description, not the PR title or commit message). E.g. using Closes #130486 or Fixes #130486.

Resolved

Also, the title should be descriptive, e.g. "[libc++] Documentation for _LIBCPP_REMOVE_TRANSITIVE_INCLUDES".

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[ldionne]

Thanks for adding this documentation! LGTM modulo my comment.

[ldionne]

@martinlicht Could you please disable Github email hiding so we can commit this with proper attribution?

[ldionne]

Ping @martinlicht , waiting for Github email hiding.

[martinlicht]

Ping @martinlicht , waiting for Github email hiding.

Should be good now.

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[mordante]

Ping @martinlicht , waiting for Github email hiding.

Should be good now.

Thanks! I've landed the patch on your behalf.