Rule dependencies' behaviour is strange, possibly broken or poorly documented

根据提供的 Rakefile 重现报告：先运行 rake、rake test.pre、rake test0.txt 和 rake test.txt，然后修改 test.pre 和 test0.pre 后再次运行。跟踪 Rake 的规则依赖解析和时间戳处理。完成标准是依赖行为得到修正或有明确文档说明，并且两个案例都有回归覆盖。

Consider this Rakefile:

require 'rake/clean'

task default: :test
task test: 'test.txt'

file 'test.txt' => 'test0.txt'

rule '.txt' => '.pre' do |t|
  sh 'cp', t.source, t.name
end

rule '.pre' do |t|
  sh 'touch', t.name
end

CLEAN.include('*.pre')
CLOBBER.include('*.txt')

This Rakefile demonstrates 2 related issues.

The implicit dependency test.pre is not built automatically

In a folder containing only this Rakefile, try:

$ rake
touch test0.pre
cp test0.pre test0.txt
cp test.pre test.txt
cp: cannot stat 'test.pre': No such file or directory
rake aborted!
Command failed with status (1): [cp test.pre test.txt...]
[...]

This creates test0.pre and test0.txt, but fails to create test.pre and test.txt.

However, the following sequence of commands works without issues:

$ rake test.pre
touch test.pre
$ rake
touch test0.pre
cp test0.pre test0.txt
cp test.pre test.txt

Thus, rake knows how to build test.pre, but skips it unless asked explicitly.

Note that despite skipping test.pre, rake builds test0.pre automatically, while both are dependencies by the same rule.

In fact, starting from a folder containing only this Rakefile,

• rake test0.txt works,
• rake test.txt fails.

Updating test.pre does not trigger rebuilding of test.txt

Assume that everything has been built with

$ rake test.pre
$ rake

Now, try this:

$ touch test.pre
$ rake

Nothing happens.

Now, try:

$ touch test0.pre
$ rake
cp test0.pre test0.txt
cp test.pre test.txt

This triggers rebuilding.

Rake version

rake version: 13.0.6.