CMake: generate chpl-language-server `.cls-commands.json` by DanilaFe · Pull Request #28427 · chapel-lang/chapel

DanilaFe · 2026-02-19T22:42:43Z

This enables editors to properly make sense of a project generated with CMake.

Testing

my minimal example generates .cls-commands.json when the environment variable is set.

Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

The idea is to make things work with CMake. CMake explicitly computes the Chapel executable path. This is great, but `chpl-shim` isn't very good at handling this, since its whole modus operandi is to place itself as 'chpl' in the PATH, which CMake circumvents. To make things work, * Allow calling code to override 'CHPL_SHIM_REAL_COMPILER_PATH' (so that it's not read by chpl-shim from the PATH variable, which would violate whatever CMake computed). * Have CMake invoke the linking command as 'chpl' (no explicit path) but provide 'CHPL_SHIM_REAL_COMPILER_PATH' (with the explicit path). This way, CMake invokes `chpl-shim chpl <args>`, `chpl-shim` places hooks into that call and parses the arguments (thus generating JSON), and finally it reads the environment variable to invoke the compiler CMake intends. Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

jabraham17 · 2026-02-19T22:47:42Z

doc/rst/usingchapel/compiling.rst

+   mkdir build && cd build
+   cmake .. -CMAKE_EXPORT_CHPL_COMMANDS=ON
+   cmake --build .
+   cd .. && ln -s build/.cls_commands.json .cls_commands.json


This is a bit unfortunate. We should consider adding a flag to CLS to specify the .cls-commands to use

Maybe, but that's not a flag that can be passed in general since CLS starts up in an arbitrary folder. Not to mention in VSCode, it starts up in potentially a different folder. So as far as I can see:

Using the flag with an absolute path is not possible, since that hardcodes CLS to only one project (as opposed to any project your editor opens)

Using the flag with a relative path doesn't work since that relative path need no exist

I suppose we could configure .cls-commands.json to allow pointing to a DIFFERENT .cls-commands.json, but isn't that a worse symlink?

FWIW, I use symlinks like this with compile-commands.json and C/C++.

FWIW, I use symlinks like this with compile-commands.json and C/C++.

👍

jabraham17 · 2026-02-19T22:47:59Z

doc/rst/usingchapel/compiling.rst

+   mkdir build && cd build
+   cmake .. -CMAKE_EXPORT_CHPL_COMMANDS=ON
+   cmake --build .
+   cd .. && ln -s build/.cls_commands.json .cls_commands.json


also note, its cls-commands, not cls_commands

I knew it looked wrong!

jabraham17 · 2026-02-19T22:52:40Z

util/cmake/CMakeCHPLInformation.cmake

 set(CMAKE_CHPL_LINK_EXECUTABLE "<CMAKE_CHPL_COMPILER> -o <TARGET> <OBJECTS> <FLAGS> <LINK_FLAGS> <LINK_LIBRARIES>")
+if(CMAKE_EXPORT_CHPL_COMMANDS)
+  # Get the directory containing the chpl compiler to find chpl-shim
+  get_filename_component(CHPL_BIN_DIR "${CMAKE_CHPL_COMPILER}" DIRECTORY)
+  set(CHPL_SHIM_SCRIPT "${CHPL_BIN_DIR}/chpl-shim")
+
+  message(STATUS "CMAKE_EXPORT_CHPL_COMMANDS is ON, checking for chpl-shim at ${CHPL_SHIM_SCRIPT}")
+
+  if(EXISTS "${CHPL_SHIM_SCRIPT}")
+    # Use chpl-shim as a wrapper to generate .cls-commands.json
+    # Note: chpl-shim expects to be called as 'chpl-shim chpl <args>', not with full path
+    message(STATUS "Using chpl-shim to generate .cls-commands.json")
+    set(CMAKE_CHPL_LINK_EXECUTABLE "<CMAKE_COMMAND> -E env CHPL_SHIM_REAL_COMPILER_PATH=${CMAKE_CHPL_COMPILER} ${CHPL_SHIM_SCRIPT} chpl -o <TARGET> <OBJECTS> <FLAGS> <LINK_FLAGS> <LINK_LIBRARIES>")


anyway to reduce the duplication between the two link commands?

jabraham17 · 2026-02-19T22:54:45Z

util/cmake/CMakeCHPLInformation.cmake

+    # Use chpl-shim as a wrapper to generate .cls-commands.json
+    # Note: chpl-shim expects to be called as 'chpl-shim chpl <args>', not with full path


Feels like that's a hard limitation without dynamic loading magic (whatever bear does)

jabraham17 · 2026-02-19T22:55:06Z

util/cmake/CMakeCHPLInformation.cmake

+  if(EXISTS "${CHPL_SHIM_SCRIPT}")
+    # Use chpl-shim as a wrapper to generate .cls-commands.json
+    # Note: chpl-shim expects to be called as 'chpl-shim chpl <args>', not with full path
+    message(STATUS "Using chpl-shim to generate .cls-commands.json")


nit, this message will be printed when configuring, not when chpl-shim is actually used

Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

jabraham17

except for the docs typo, looks good!

jabraham17 · 2026-02-19T23:21:40Z

doc/rst/usingchapel/compiling.rst

+
+To enable use of CMake-based projects with the :ref:`language server <readme-chpl-language-server>`,
+the CMake integration provides a special variable ``CMAKE_EXPORT_CHPL_COMMANDS``.
+When set to ``ON``, CMake will generate a file named ``.cls_commands.json`` in


this needs updates too :)

DanilaFe added 5 commits February 19, 2026 14:45

Adjust chpl-shim to work with files generated by CMake

16ec0a4

Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

Tweak chpl-shim.py to be workable from CMake

74e840d

Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

Add CMake support for chpl-shim

04d9e15

Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

Add docs

c31e72d

Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

DanilaFe force-pushed the cmake-generate-cls-commands branch from 1c4c962 to c31e72d Compare February 19, 2026 22:45

jabraham17 reviewed Feb 19, 2026

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Signed-off-by: Danila Fedorin <daniel.fedorin@hpe.com>

jabraham17 approved these changes Feb 19, 2026

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CMake: generate chpl-language-server `.cls-commands.json`#28427

CMake: generate chpl-language-server `.cls-commands.json`#28427
DanilaFe wants to merge 6 commits intochapel-lang:mainfrom
DanilaFe:cmake-generate-cls-commands

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		# Use chpl-shim as a wrapper to generate .cls-commands.json
		# Note: chpl-shim expects to be called as 'chpl-shim chpl <args>', not with full path

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DanilaFe commented Feb 19, 2026

Testing

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