Building boost to web assembly fails

[bruno-j-nicoletti]

Make sure you completed the following tasks

• I searched the discussions
• I searched the closed and open issues
• I read the contribution guidelines

Environment and version details

• Operating System+version: MacOS 12.6.7 (reproducible on Linux as well), building to emsdk/3.1.44
• Compiler+version: emcc
• Shell: bash
• B2 Version: B2 4.9-git
• B2 Configuration: NA

NA

Brief problem description

When attempting to build boost libraries via conan to webassembly, boost fails to build with the following message...

Error: ambiguity found when searching for best transformation
Trying to produce type 'SEARCHED_LIB' from: 
Generators that succeeded:
 -  searched-lib-generator
 -  emscripten.searched-lib-generator
First generator produced: 
 -  { %.no-action-z.SEARCHED_LIB }
Second generator produced: 
 -  { %.no-action-z.SEARCHED_LIB }

The issue can be fixed by patching the b2 jamfile src/tools/emscripten.jam that boost 1.83.0 depends on as follows....

9d8
< import generators ;
55,57d53
< generators.override builtin.lib-generator : emscripten.prebuilt ;
< generators.override emscripten.searched-lib-generator : searched-lib-generator ;
<

That patch can't be applied to src/tools/emscripten.jam as the file on the main branch has moved on.

Steps to reproduce the issue

With conan2 installed, and the following conanfile.py...

from conan import ConanFile

class BorkingBoostBuildConan(ConanFile):
    name = "BNS"
    version = "0.0.1"
    settings = "os", "compiler", "build_type", "arch"
    generators = "CMakeToolchain", "CMakeDeps"

    def requirements(self) :
        self.requires("boost/1.83.0")

The following file ./emsdkProfile

settings]
arch=wasm
compiler=clang
compiler.cppstd=23
compiler.libcxx=libc++
compiler.version=16
os=Emscripten
build_type=Debug

[tool_requires]
*: emsdk/3.1.44

[conf]
tools.build:cxxflags=["-fwasm-exceptions", "-pthread"]

[buildenv]
LDFLAGS="-fwasm-exceptions", "-pthread", "-s PROXY_TO_PTHREAD", "-sALLOW_MEMORY_GROWTH"

and the following file macosRelease

os=Macos
arch=x86_64
compiler=apple-clang
compiler.version=14
compiler.cppstd=17
compiler.libcxx=libc++

the command...

conan install --output-folder=build --build=missing -pr:b ./macosRelease -pr:h ./emsdkProfile ./conanfile.py -o boost/\*:with_stacktrace_backtrace=False

results in the following output...

======== Input profiles ========
Profile host:
[settings]
arch=wasm
build_type=Debug
compiler=clang
compiler.cppstd=23
compiler.libcxx=libc++
compiler.version=16
os=Emscripten
[options]
boost/*:with_stacktrace_backtrace=False
[tool_requires]
*: emsdk/3.1.44
[conf]
tools.build:cxxflags=['-fwasm-exceptions', '-pthread']
[buildenv]
LDFLAGS="-fwasm-exceptions", "-pthread", "-s PROXY_TO_PTHREAD", "-sALLOW_MEMORY_GROWTH"

Profile build:
[settings]
arch=x86_64
build_type=Release
compiler=apple-clang
compiler.cppstd=17
compiler.libcxx=libc++
compiler.version=14
os=Macos


======== Computing dependency graph ========
boost/1.83.0: Not found in local cache, looking in remotes...
boost/1.83.0: Checking remote: conancenter
boost/1.83.0: Downloaded recipe revision 8be129e9ab6e00b3d74810626cdbea9c
Graph root
    conanfile.py (BNS/0.0.1): /Users/bruno/Work/boostHell/conanfile.py
Requirements
    boost/1.83.0#8be129e9ab6e00b3d74810626cdbea9c - Downloaded (conancenter)
    bzip2/1.0.8#411fc05e80d47a89045edc1ee6f23c1d - Cache
    zlib/1.2.13#e377bee636333ae348d51ca90874e353 - Cache
Build requirements
    b2/4.9.6#53783bdbbdbb6c13732b25f1f6ea6c58 - Cache
    emsdk/3.1.44#a6d941a26a1c416d25e3505805703a58 - Cache
    nodejs/16.3.0#fbb644235845086644bebd53e452595b - Cache

======== Computing necessary packages ========
boost/1.83.0: Checking 9 compatible configurations:
boost/1.83.0: '8ccee61c8b07220fbe5a5fe74c8fdd6ec574193c': compiler.cppstd=11
boost/1.83.0: 'a3ec0237a73d4381ea6d8f5d310312c8472605be': compiler.cppstd=gnu11
boost/1.83.0: '9a14321c477848010eaa8836bc2fa137e41157bd': compiler.cppstd=14
boost/1.83.0: '32a6f7ecb44b2c50fdf25e2885ef3924125749ca': compiler.cppstd=gnu14
boost/1.83.0: '51e93e6472834c7b40fed494ecae8a37f4cc58c8': compiler.cppstd=17
boost/1.83.0: 'e90c8db2bb1ba4b86fba99ea6a9829bc29ace775': compiler.cppstd=gnu17
boost/1.83.0: '40b8a4ed65a40d9ee6e119cf4858e306fd7c96c7': compiler.cppstd=20
boost/1.83.0: '7240f756ad186990dabe01380fea1b68d3c1588c': compiler.cppstd=gnu20
boost/1.83.0: 'c8188ef9f0ca923334a404e7bce08a82ac81e945': compiler.cppstd=gnu23
Requirements
    boost/1.83.0#8be129e9ab6e00b3d74810626cdbea9c:aaaec01a32da69642eb212b65576d882d068e126 - Build
    bzip2/1.0.8#411fc05e80d47a89045edc1ee6f23c1d:6d96f99e9965a4797bd36a3301a7da9699f8681c#0492a23ca06d25192089e02bdba7c31a - Cache
    zlib/1.2.13#e377bee636333ae348d51ca90874e353:e3fac8d3f9347da32209118b429e89851f8a417d#51e5027420bc1deea4d32449691dbf65 - Cache
Build requirements
    b2/4.9.6#53783bdbbdbb6c13732b25f1f6ea6c58:82339cc4d6db7990c1830d274cd12e7c91ab18a1#f375c196e601fb716b2bd5018c871c78 - Cache
    emsdk/3.1.44#a6d941a26a1c416d25e3505805703a58:82339cc4d6db7990c1830d274cd12e7c91ab18a1#8dbf4ab5c71e04b6ea14e90c5640f80f - Cache
    nodejs/16.3.0#fbb644235845086644bebd53e452595b:82339cc4d6db7990c1830d274cd12e7c91ab18a1#d0751e90bacaaf8eed3c0c2b10bd05eb - Cache

======== Installing packages ========
b2/4.9.6: Already installed! (1 of 6)
nodejs/16.3.0: Already installed! (2 of 6)
nodejs/16.3.0: Appending PATH environment variable: /Users/bruno/.conan2/p/nodejf10c1d8c12c70/p/bin
nodejs/16.3.0: Appending PATH environment variable: /Users/bruno/.conan2/p/nodejf10c1d8c12c70/p/bin
bzip2/1.0.8: Already installed! (3 of 6)
zlib/1.2.13: Already installed! (4 of 6)
emsdk/3.1.44: Already installed! (5 of 6)
boost/1.83.0: Sources downloaded from 'conancenter'
boost/1.83.0: Calling source() in /Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src
boost/1.83.0: Downloading 122.9MB boost_1_83_0.tar.bz2
boost/1.83.0: Downloaded 85.7MB 69% boost_1_83_0.tar.bz2
boost/1.83.0: Apply patch (conan): Optional flag to specify iconv from either libc of libiconv

-------- Installing package boost/1.83.0 (6 of 6) --------
boost/1.83.0: Building from source
boost/1.83.0: Package boost/1.83.0:aaaec01a32da69642eb212b65576d882d068e126
boost/1.83.0: Building your package in /Users/bruno/.conan2/p/b/boost8525b86d413ba/b
boost/1.83.0: Calling generate()
boost/1.83.0: Generators folder: /Users/bruno/.conan2/p/b/boost8525b86d413ba/b/build-debug/conan
boost/1.83.0: Generating aggregated env files
boost/1.83.0: Generated aggregated env files: ['conanbuild.sh', 'conanrun.sh']
boost/1.83.0: Calling build()
boost/1.83.0: WARN: replace_in_file didn't find pattern '/* thread_local */' in '/Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/boost/stacktrace/detail/libbacktrace_impls.hpp' file.
boost/1.83.0: WARN: replace_in_file didn't find pattern '/* static __thread */' in '/Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/boost/stacktrace/detail/libbacktrace_impls.hpp' file.
boost/1.83.0: WARN: replace_in_file didn't find pattern 'local generic-os = [ set.difference $(all-os) : aix darwin vxworks solaris osf hpux ] ;' in '/Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/tools/build/src/tools/gcc.jam' file.
boost/1.83.0: WARN: replace_in_file didn't find pattern 'local no-threading = android beos haiku sgi darwin vxworks ;' in '/Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/tools/build/src/tools/gcc.jam' file.
boost/1.83.0: WARN: Patching user-config.jam
boost/1.83.0: WARN: 
using zlib : 1.2.13 : <include>"/Users/bruno/.conan2/p/b/zlib92366dd24ff76/p/include" <search>"/Users/bruno/.conan2/p/b/zlib92366dd24ff76/p/lib" <name>z ;
using bzip2 : 1.0.8 : <include>"/Users/bruno/.conan2/p/b/bzip2e5e0f698f6100/p/include" <search>"/Users/bruno/.conan2/p/b/bzip2e5e0f698f6100/p/lib" <name>bz2 ;
using "emscripten" :  :  "/Users/bruno/.conan2/p/b/emsdk8fd9873fdac27/p/bin/upstream/emscripten/em++" : 
<archiver>"/Users/bruno/.conan2/p/b/emsdk8fd9873fdac27/p/bin/upstream/emscripten/emar" <ranlib>"/Users/bruno/.conan2/p/b/emsdk8fd9873fdac27/p/bin/upstream/emscripten/emranlib" <cxxflags>"-fwasm-exceptions -pthread"  ;
boost/1.83.0: Cross building, detecting compiler...
boost/1.83.0: Cross building flags: []
boost/1.83.0: WARN: b2 -q numa=on address-model=32 --layout=system --user-config=/Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/tools/build/user-config.jam -sNO_ZLIB=0 -sNO_BZIP2=0 -sNO_LZMA=1 -sNO_ZSTD=1 boost.locale.icu=off --disable-icu boost.locale.iconv=on boost.locale.iconv.lib=libc threading=multi visibility=hidden link=static variant=debug --with-atomic --with-chrono --with-container --with-context --with-contract --with-coroutine --with-date_time --with-exception --with-fiber --with-filesystem --with-graph --with-iostreams --with-json --with-locale --with-log --with-math --with-nowide --with-program_options --with-random --with-regex --with-serialization --with-stacktrace --with-system --with-test --with-thread --with-timer --with-type_erasure --with-url --with-wave toolset=emscripten cxxflags=-std=c++2b pch=on linkflags="" cxxflags="-fPIC -DBOOST_STACKTRACE_ADDR2LINE_LOCATION=/usr/bin/addr2line" install --prefix=/Users/bruno/.conan2/p/b/boost8525b86d413ba/p -j16 --abbreviate-paths -d0 --debug-configuration --build-dir="/Users/bruno/.conan2/p/b/boost8525b86d413ba/b/build-debug"
boost/1.83.0: RUN: b2 -q numa=on address-model=32 --layout=system --user-config=/Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/tools/build/user-config.jam -sNO_ZLIB=0 -sNO_BZIP2=0 -sNO_LZMA=1 -sNO_ZSTD=1 boost.locale.icu=off --disable-icu boost.locale.iconv=on boost.locale.iconv.lib=libc threading=multi visibility=hidden link=static variant=debug --with-atomic --with-chrono --with-container --with-context --with-contract --with-coroutine --with-date_time --with-exception --with-fiber --with-filesystem --with-graph --with-iostreams --with-json --with-locale --with-log --with-math --with-nowide --with-program_options --with-random --with-regex --with-serialization --with-stacktrace --with-system --with-test --with-thread --with-timer --with-type_erasure --with-url --with-wave toolset=emscripten cxxflags=-std=c++2b pch=on linkflags="" cxxflags="-fPIC -DBOOST_STACKTRACE_ADDR2LINE_LOCATION=/usr/bin/addr2line" install --prefix=/Users/bruno/.conan2/p/b/boost8525b86d413ba/p -j16 --abbreviate-paths -d0 --debug-configuration --build-dir="/Users/bruno/.conan2/p/b/boost8525b86d413ba/b/build-debug"
notice: found boost-build.jam at /Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/boost-build.jam
notice: loading B2 from /Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/kernel/bootstrap.jam
notice: Searching '/etc' '/Users/bruno' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/kernel' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/util' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/build' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/tools' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/contrib' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/.' for site-config configuration file 'site-config.jam'.
notice: Configuration file 'site-config.jam' not found in '/etc' '/Users/bruno' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/kernel' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/util' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/build' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/tools' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/contrib' '/Users/bruno/.conan2/p/b24bd1c02e3b59e/p/bin/.b2/.'.
notice: Loading explicitly specified user configuration file:
    /Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/tools/build/user-config.jam
notice: Searching '/Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/tools/build' for user-config configuration file 'user-config.jam'.
notice: Loading user-config configuration file 'user-config.jam' from '/Users/bruno/.conan2/p/boostf43c9e9f0bf53/s/src/tools/build'.
notice: [zlib] Using pre-installed library
notice: [zlib] Condition
notice: [bzip2] Using pre-installed library
notice: [bzip2] Condition
notice: will use '/Users/bruno/.conan2/p/b/emsdk8fd9873fdac27/p/bin/upstream/emscripten/em++' for emscripten, condition <toolset>emscripten-3.1.44
notice: [zlib] zlib is already configured
notice: [bzip2] bzip is already configured
notice: iostreams: not using lzma compression 
notice: iostreams: not using zstd compression 
notice: [python-cfg] Configuring python...
notice: [python-cfg] Checking interpreter command "python"...
notice: [python-cfg] running command 'python -c "from sys import *; print('version=%d.%d\nplatform=%s\nprefix=%s\nexec_prefix=%s\nexecutable=%s' % (version_info[0],version_info[1],platform,prefix,exec_prefix,executable))" 2>&1'
notice: [python-cfg] ...requested configuration matched!
notice: [python-cfg] Details of this Python configuration:
notice: [python-cfg]   interpreter command: "python"
notice: [python-cfg]   include path: "/Users/bruno/venv3_11/include/python3.11"
notice: [python-cfg]   library path: "/Users/bruno/venv3_11/lib/python3.11/config" "/Users/bruno/venv3_11/lib"
notice: [python-cfg] Checking for NumPy...
notice: [python-cfg] running command 'python -c "import sys; sys.stderr = sys.stdout; import numpy; print(numpy.get_include())"'
notice: [python-cfg] NumPy enabled
notice: [python-cfg] no framework directory found; using library path
Performing configuration checks

    - default address-model    : 32-bit [1]
    - default architecture     : none [1]
    - x86                      : no [2]
    - arm                      : no [2]
    - mips1                    : no [2]
    - power                    : no [2]
    - sparc                    : no [2]
error: No best alternative for libs/context/build/asm_sources with <abi>sysv <address-model>32 <asynch-exceptions>off <binary-format>mach-o <boost.locale.iconv.lib>libc <boost.locale.iconv>on <boost.locale.icu>off <closure>off <context-impl>fcontext <coverage>off <debug-symbols>on <deduced-address-model>32 <embind>off <exception-handling>on <extern-c-nothrow>off <inlining>off <link-optimization>off <link>static <numa>on <optimization>off <os>MACOSX <pch>on <preserve-test-targets>on <profiling>off <python-debugging>off <python>3.11 <relevant>abi <relevant>address-model <relevant>architecture <relevant>binary-format <relevant>toolset <rtti>on <runtime-debugging>on <runtime-link>shared <stdlib>native <strip>off <target-os>darwin <testing.execute>on <threadapi>pthread <threading>multi <toolset-emscripten:version>3.1.44 <toolset>emscripten <variant>debug <vectorize>off <visibility>hidden <warnings-as-errors>off <warnings>on
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>elf <threading>multi <toolset>qcc
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>aapcs <address-model>32 <architecture>arm <binary-format>pe <threading>multi <toolset>msvc
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>aapcs <address-model>64 <architecture>arm <binary-format>pe <threading>multi <toolset>msvc
    no match: <abi>sysv <address-model>64 <architecture>loongarch <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>o32 <address-model>32 <architecture>mips <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>o32 <address-model>32 <architecture>mips <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>n64 <address-model>64 <architecture>mips <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>n64 <address-model>64 <architecture>mips <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>mach-o <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>xcoff <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>power <binary-format>xcoff <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>mach-o <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>xcoff <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>power <binary-format>xcoff <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32_64 <architecture>power <binary-format>mach-o <threading>multi
    no match: <abi>sysv <address-model>64 <architecture>riscv <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>riscv <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>s390x <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>s390x <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>intel
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>32 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>clang
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>clang-win
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>gcc
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>intel
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>msvc
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>embarcadero
    no match: <abi>ms <address-model>32 <architecture>x86 <binary-format>pe <threading>multi <toolset>borland
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>elf <threading>multi <toolset>intel
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>clang
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>gcc
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>darwin
    no match: <abi>sysv <address-model>64 <architecture>x86 <binary-format>mach-o <threading>multi <toolset>intel
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>clang
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>clang-win
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>gcc
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>intel
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>msvc
    no match: <abi>ms <address-model>64 <architecture>x86 <binary-format>pe <threading>multi <toolset>embarcadero
    no match: <abi>x32 <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>clang
    no match: <abi>x32 <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>gcc
    no match: <abi>x32 <address-model>32 <architecture>x86 <binary-format>elf <threading>multi <toolset>intel
    no match: <abi>sysv <address-model>32_64 <architecture>x86 <binary-format>mach-o <threading>multi
    no match: <abi>sysv <architecture>arm+x86 <binary-format>mach-o <threading>multi
    - has std::atomic_ref      : no [2]
    - has statx                : no [2]
    - has statx syscall        : no [2]
    - has init_priority attribute : yes [2]
    - has stat::st_blksize     : yes [2]
    - has stat::st_mtim        : yes [2]
    - has stat::st_mtimensec   : no [2]
    - has stat::st_mtimespec   : no [2]
    - has stat::st_birthtim    : no [2]
    - has stat::st_birthtimensec : no [2]
    - has stat::st_birthtimespec : no [2]
    - has fdopendir(O_NOFOLLOW) : yes [2]
    - has dirent::d_type       : yes [2]
    - has POSIX *at APIs       : yes [2]
    - cxx11_auto_declarations  : yes [2]
    - cxx11_constexpr          : yes [2]
    - cxx11_defaulted_functions : yes [2]
    - cxx11_final              : yes [2]
    - cxx11_hdr_mutex          : yes [2]
    - cxx11_hdr_tuple          : yes [2]
    - cxx11_lambdas            : yes [2]
    - cxx11_noexcept           : yes [2]
    - cxx11_nullptr            : yes [2]
    - cxx11_rvalue_references  : yes [2]
    - cxx11_template_aliases   : yes [2]
    - cxx11_thread_local       : yes [2]
    - cxx11_variadic_templates : yes [2]
    - has_icu builds           : no [2]
Error: ambiguity found when searching for best transformation
Trying to produce type 'SEARCHED_LIB' from: 
Generators that succeeded:
 -  searched-lib-generator
 -  emscripten.searched-lib-generator
First generator produced: 
 -  { %.no-action-z.SEARCHED_LIB }
Second generator produced: 
 -  { %.no-action-z.SEARCHED_LIB }


boost/1.83.0: ERROR: 
Package 'aaaec01a32da69642eb212b65576d882d068e126' build failed
boost/1.83.0: WARN: Build folder /Users/bruno/.conan2/p/b/boost8525b86d413ba/b/build-debug
*********************************************************
Recipe 'boost/1.83.0' cannot build its binary
It is possible that this recipe is not Conan 2.0 ready
If the recipe comes from ConanCenter check: https://conan.io/cci-v2.html
If it is your recipe, check if it is updated to 2.0
*********************************************************

ERROR: boost/1.83.0: Error in build() method, line 887
	self.run(full_command)
	ConanException: Error 1 while executing

Actual behavior summary

Boost fails to build vai conan when compiling to webassembly.

Attach, or place here, log output showing the bug including running
with the options: -d2 --debug-configuration

Expected behavior summary

It should build to web assembly and not fail.

[Kojoley]

Error: ambiguity found when searching for best transformation
Trying to produce type 'SEARCHED_LIB' from: 
Generators that succeeded:
 -  searched-lib-generator
 -  emscripten.searched-lib-generator
First generator produced: 
 -  { %.no-action-z.SEARCHED_LIB }
Second generator produced: 
 -  { %.no-action-z.SEARCHED_LIB }

The issue can be fixed by patching the b2 jamfile src/tools/emscripten.jam that boost 1.83.0 depends on as follows....

This has been fixed in #225 and emscripten support overhaul happened in #310

error: No best alternative for libs/context/build/asm_sources with sysv 32 off mach-o <boost.locale.iconv.lib>libc <boost.locale.iconv>on <boost.locale.icu>off off fcontext off on 32 off on off off off static on off MACOSX on on off off 3.11 abi address-model architecture binary-format toolset on on shared native off darwin <testing.execute>on pthread multi toolset-emscripten:version3.1.44 emscripten debug off hidden off on

It's not a b2 issue. AFAIK emscripten is not supported by Boost.Context, file an issue there.