bug: mise run doesn't track deleted, etc. dependencies

[arxanas]

I didn't see anything obviously related in Discussions.

Setup:

$ cat mise.toml
[tasks.build]
description = "Build"
sources = ["*.in"]
outputs = ["out"]
run = "cat *.in >out"
$ echo 'foo' >foo.in
$ echo 'bar' >bar.in

$ mise run build
[build] $ cat *.in >out
$ cat out
bar
foo

Current behavior:

$ rm foo.in
$ mise run build  # wrong, should rebuild
[build] sources up-to-date, skipping
$ cat out  # wrong, still has `foo`:
bar
foo

The correct behavior would be to rebuild out in this case, which we can demonstrate by running with --force and observing a behavioral difference:

$ mise run build --force
[build] $ cat *.in >out
$ cat out  # correct, reflects deleted `foo`:
bar

You might call this the "Makefile problem"? Fundamentally, you need to track the old state of the build graph to determine when the build graph has changed.

The easiest solution is probably to hash the inputs and outputs and store the mapping somewhere. On a rebuild, recompute the input hashes, look up the corresponding output hashes, and skip the rebuild if they match.

• In addition to the source files, the actual definition of the build task is itself an input.
  • I suppose that might even include the transitive closure of the definitions/hashes of its dependency tasks?
• The environment variables and executable are also technically inputs, although perhaps we don't care in practice.
• Alternatively, generate a build plan and shell out to a build system like ninja 😉.

There's also all the incidental problems as per mtime comparison considered harmful. For example, I didn't check, but I assume that mise will also fail to rebuild when a file is moved but its mtime hasn't changed.