commit 2150866288e5dcdf6117a96cc427158e32c221a3
author Michael Bolin <mbolin@fb.com> Wed Sep 11 12:29:58 2013 -0700
committer Michael Bolin <mbolin@fb.com> Thu Sep 19 15:25:01 2013 -0700
tree fe811cf1c6d82c6ecd168b5d1f0c571a96f6a125
parent 8fbbbda4a6d4b9843eb741acd898346be1730bc2

Stop storing the build file on BuildTarget.

Summary:
Historically, `BuildTarget` required its corresponding build file to be passed in
as a constructor argument, where preconditions verified that the build file
existed and its path matched the target's path. These strong preconditions
were introduced in hopes of preventing errors.

In practice, this was a bad choice because it made creating a `BuildTarget`
more difficult, as its constructor had to touch the filesystem. As one could
imagine, this was quite a pain when it came to writing unit tests. Instead of
being a typesafe string, `BuildTarget` was much more complicated. We had
to go to great pains to tolerate null build files in fake `BuildTarget`s for tests.

This diff removes that complexity. Now, to get the build file associated with
a `BuildTarget`, one must invoke `BuildTarget`'s new
`getBuildFile(ProjectFilesystem)` method, which throws a
`MissingBuildFileException` if there is no file at the path that corresponds
to the `BuildTarget`.

The `MissingBuildFileException` introduced in this diff is similar
to the `NoSuchBuildTargetException` in the `com.facebook.buck.parser`
package. The problem is that the `parser` package depends on the `model`
package, so a `BuildTarget` could not throw a `NoSuchBuildTarget` exception
itself without unwinding quite a few things. This is why the new `MissingBuildFileException`
was introduced.

Further, a common superclass, `BuildTargetException`, was introduced in order to
simplify catch blocks throughout the code. Its two child classes are
`NoSuchBuildTargetException` and `MissingBuildFileException`.

This diff makes `BuildTargetFactory` largely unnecessary, though it does
not delete it outright. Replacing the `BuildTarget(String, String)` constructor
with a `BuildTarget(String)` constructor that takes a single parameter and
splits on the colon itself will ultimately eliminate the need for
`BuildTargetFactory` altogether. This will be done in a follow-up diff.

Test Plan: Sandcastle builds.