Add initial support for {CPP}-26 Contracts for GCC based toolsets (like clang).

doc/src/history.adoc

@@ -1,6 +1,12 @@
 [[b2.history]]
 = History
 
+== Version 5.4.0
+
+* *New*: Add initial support for {CPP}-26 Contracts for GCC based toolsets
+  (like clang).
+  -- _René Ferdinand Rivera Morell_
+
 == Version 5.3.3
 
 * Fix `stdlib=libc++` feature being applied to compiles other than {CPP}.

doc/src/reference.adoc

@@ -286,6 +286,7 @@ include::../../src/tools/features/warnings-feature.jam[tag=doc]
 include::../../src/tools/features/translate-path-feature.jam[tag=doc]
 include::../../src/tools/features/lto-feature.jam[tag=doc]
 include::../../src/tools/features/response-file-feature.jam[tag=doc]
+include::../../src/tools/features/contracts-feature.jam[tag=doc]
 
 [[b2.reference.tools]]
 == Builtin tools

example/contracts/hello.cpp

@@ -0,0 +1,21 @@
+// Copyright 2025 René Ferdinand Rivera Morel
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.txt or copy at
+// https://www.bfgroup.xyz/b2/LICENSE.txt)
+
+// tag::source[]
+#include <contracts>
+#include <iostream>
+
+int f(const int x) pre(x != 0) post(r : r != x)
+{
+	return x + 1;
+}
+
+int main()
+{
+	std::cout << "Hello!\n";
+	f(1);
+	f(0);
+}
+// end::source[]

example/contracts/jamroot.jam

@@ -0,0 +1,14 @@
+# Copyright 2008 Jurko Gospodnetic
+# Copyright 2025 René Ferdinand Rivera Morell
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE.txt or https://www.bfgroup.xyz/b2/LICENSE.txt)
+
+project
+    : requirements
+        <contracts>on
+        <contracts-semantic>enforce
+        <toolset>clang:<stdlib>libc++
+        <cxxstd>23
+    ;
+
+exe hello : hello.cpp ;

example/contracts/readme.adoc

@@ -0,0 +1,47 @@
+////
+Copyright 2008 Jurko Gospodnetic
+Copyright 2025 René Ferdinand Rivera Morell
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE.txt or https://www.bfgroup.xyz/b2/LICENSE.txt)
+////
+
+= Hello
+
+This example shows a very basic Boost Build project set up so it compiles a
+single executable which makes use of contracts from a single source file:
+
+.`hello.cpp`
+[source,cpp]
+----
+include::../../example/contracts/hello.cpp[tag=source]
+----
+
+Our `jamroot.jam` is minimal and only specifies one `exe` target for the
+program:
+
+.`jamroot.jam`
+[source,jam]
+----
+include::jamroot.jam[]
+----
+
+Building the example yields:
+
+[source,bash]
+----
+> cd /example/hello
+> b2
+...found 12 targets...
+...updating 8 targets...
+clang-linux.compile.c++ bin/clang-linux-22.0~contracts/debug/contracts-on-enforce/cxxstd-23-iso/stdlib-libc++/hello.o
+clang-linux.link bin/clang-linux-22.0~contracts/debug/contracts-on-enforce/cxxstd-23-iso/stdlib-libc++/hello
+
+...updated 8 targets...
+> LD_LIBRARY_PATH=/opt/clang-ericwf-contracts-trunk/lib/x86_64-unknown-linux-gnu/ bin/clang-linux-22.0~contracts/debug/contracts-on-enforce/cxxstd-23-iso/stdlib-libc++/hello
+Hello!
+hello.cpp:11: pre(x != 0) failed
+libc++abi: terminating
+Aborted                    (core dumped) LD_LIBRARY_PATH=/opt/clang-ericwf-contracts-trunk/lib/x86_64-unknown-linux-gnu/ bin/clang-linux-22.0~contracts/debug/contracts-on-enforce/cxxstd-23-iso/stdlib-libc++/hello
+----
+
+NOTE: The actual paths will depend on your configuration.

src/build/version.jam

@@ -9,8 +9,8 @@ import numbers ;
 
 # Mirror engine JAM_VERSION
 .major = 5 ;
-.minor = 3 ;
-.patch = 3 ;
+.minor = 4 ;
+.patch = 0 ;
 
 
 rule build ( )

src/engine/patchlevel.h

@@ -13,5 +13,5 @@ https://www.bfgroup.xyz/b2/LICENSE.txt)
 */
 
 #define VERSION_MAJOR 5
-#define VERSION_MINOR 3
-#define VERSION_PATCH 3
+#define VERSION_MINOR 4
+#define VERSION_PATCH 0

src/tools/features/contracts-feature.jam

@@ -0,0 +1,48 @@
+# Copyright 2025 René Ferdinand Rivera Morel
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE.txt or copy at
+# https://www.bfgroup.xyz/b2/LICENSE.txt)
+
+import feature ;
+
+#| tag::doc[]
+
+[[b2.builtin.features.contracts]]`contracts`::
+*Allowed values:* `on`.
++
+Enables use of experimental use of {CPP}-26 Contracts (P2900). Enabling
+contracts has additional requirements when using them with at least clang. See
+https://contracts.efcs.ca/ for details. For B2 the requirements amount to
+needing to use `<toolset>clang:<stdlib>libc++` and `<cxxstd>23`.
+
+|# # end::doc[]
+
+feature.feature contracts
+    : on
+    : optional propagated link-incompatible ;
+
+#| tag::doc[]
+
+[[b2.builtin.features.contracts-sematic]]`contracts-semantic`::
+*Subfeature of* `contracts`
++
+*Allowed values:* `enforce', 'quick_enforce', 'observe', 'ignore`.
++
+Specifies the contract checking semantic for the translation unit. The default
+is `enforce` for which contract checks are evaluated with violations resulting
+in error termination.
++
+`enforce`::: Contract assertions are not evaluated (contracts are disabled).
+`quick_enforce`::: Contract assertions are evaluated but violations do not
+  terminate the program.
+`observe`::: Contract assertions are evaluated and violations terminate the
+  program.
+`ignore`::: Like enforce, but uses optimized evaluation that may skip some
+  checks.
+
+|# # end::doc[]
+
+feature.subfeature contracts
+    : semantic
+    : enforce quick_enforce observe ignore
+    : ;

src/tools/gcc.jam

@@ -1,6 +1,6 @@
 # Copyright 2021 Nikita Kniazev
 # Copyright 2001 David Abrahams
-# Copyright 2002-2017 Rene Rivera
+# Copyright 2002-2025 René Ferdinand Rivera Morell
 # Copyright 2002-2003 Vladimir Prus
 # Copyright 2005 Reece H. Dunn
 # Copyright 2006 Ilya Sokolov
@@ -716,6 +716,13 @@ toolset.flags gcc.link OPTIONS <lto>on/<lto-mode>fat : -flto ;
 toolset.flags gcc.compile.c++ DEFINES <stdlib>gnu : _GLIBCXX_USE_CXX11_ABI=0 ;
 toolset.flags gcc.compile.c++ DEFINES <stdlib>gnu11 : _GLIBCXX_USE_CXX11_ABI=1 ;
 
+# Contracts
+toolset.flags gcc.compile.c++ OPTIONS <contracts>on : -fcontracts ;
+toolset.flags gcc.compile.c++ OPTIONS <contracts>on/<contracts-semantic>ignore : -fcontract-evaluation-semantic=ignore ;
+toolset.flags gcc.compile.c++ OPTIONS <contracts>on/<contracts-semantic>observe : -fcontract-evaluation-semantic=observe ;
+toolset.flags gcc.compile.c++ OPTIONS <contracts>on/<contracts-semantic>enforce : -fcontract-evaluation-semantic=enforce ;
+toolset.flags gcc.compile.c++ OPTIONS <contracts>on/<contracts-semantic>quick_enforce : -fcontract-evaluation-semantic=quick_enforce ;
+
 ###
 ### User free feature options.
 ###