If you want to make changes to Lean itself, start by building Lean from a clean checkout to make sure that everything is set up correctly. After that, read on below to find out how to set up your editor for changing the Lean source code, followed by further sections of the development manual where applicable such as on the test suite and commit convention.
If you are planning to make any changes that may affect the compilation of Lean itself, e.g. changes to the parser, elaborator, or compiler, you should first read about the bootstrapping pipeline.
You should not edit the
stage0 directory except using the commands described in that section when necessary.
You can use any of the supported editors for editing the Lean source code.
If you set up
elan as below, opening
src/ as a workspace folder should ensure that stage 0 (i.e. the stage that first compiles
src/) will be used for files in that directory.
Dev setup using elan
You can use
elan to easily
switch between stages and build configurations based on the current
directory, both for the
leanmake binaries in your shell's
PATH and inside your editor.
To install elan, you can do so, without installing a default version of Lean, using (Unix)
curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh -s -- --default-toolchain none
curl -O --location https://raw.githubusercontent.com/leanprover/elan/master/elan-init.ps1 powershell -f elan-init.ps1 --default-toolchain none del elan-init.ps1
You can use
elan toolchain link to give a specific stage build
directory a reference name, then use
elan override set to associate
such a name to the current directory. We usually want to use
for editing files in
stage1 for everything else (e.g.
# in the Lean rootdir elan toolchain link lean4 build/release/stage1 elan toolchain link lean4-stage0 build/release/stage0 # make `lean` etc. point to stage1 in the rootdir and subdirs elan override set lean4 cd src # make `lean` etc. point to stage0 anywhere inside `src` elan override set lean4-stage0
You can also use the
+toolchain shorthand (e.g.
lean +lean4-debug) to switch
toolchains on the spot.
lean4-mode will automatically use the
associated with the directory of the current file as long as
~/.elan/bin is in your
exec-path. Where Emacs sources the
exec-path from can be a bit unclear depending on your configuration, so
alternatively you can also set
You might find that debugging through elan, e.g. via
gdb lean, disables some
things like symbol autocompletion because at first only the elan proxy binary
is loaded. You can instead pass the explicit path to
bin/lean in your build
folder to gdb, or use
gdb $(elan which lean).