fix(layout): Put examples in their unit dir in new layout

Before, pre-uplifted examples were being written to
`{build-dir}/{profile}/examples/{name}-{hash}`.
Now they are being written to
`{build-dir}/{profile}/build/{pkgname}/{hash}/{name}-{hash}`.

This does not affect uplifted examples (they lack the `-{hash}`).

Pre-build-dir, these were placed in a "public" location but I don't see
a reason for that to be the case (otherwise, we'd need to switch them to
`{target-dir}/{profile}/examples/{name}-{hash}`).
In that case, I don't see a reason to treat examples as any different
than any other artifact and going in their unique build init directory.

Fixes #16302

Author: epage

src/cargo/core/compiler/build_runner/compilation_files.rs

@@ -220,7 +220,7 @@ impl<'a, 'gctx: 'a> CompilationFiles<'a, 'gctx> {
             panic!("doc tests do not have an out dir");
         } else if unit.target.is_custom_build() {
             self.build_script_dir(unit)
-        } else if unit.target.is_example() {
+        } else if unit.target.is_example() && !self.ws.gctx().cli_unstable().build_dir_new_layout {
             self.layout(unit.kind).build_dir().examples().to_path_buf()
         } else if unit.artifact.is_true() {
             self.artifact_dir(unit)

tests/testsuite/build_dir.rs

@@ -396,8 +396,8 @@ fn examples_should_output_to_build_dir_and_uplift_to_target_dir() {
 [ROOT]/foo/build-dir/debug/build/foo/[HASH]/fingerprint/example-foo
 [ROOT]/foo/build-dir/debug/build/foo/[HASH]/fingerprint/example-foo.json
 [ROOT]/foo/build-dir/debug/build/foo/[HASH]/fingerprint/invoked.timestamp
-[ROOT]/foo/build-dir/debug/examples/foo[..][EXE]
-[ROOT]/foo/build-dir/debug/examples/foo[..].d
+[ROOT]/foo/build-dir/debug/build/foo/[HASH]/deps/foo[..][EXE]
+[ROOT]/foo/build-dir/debug/build/foo/[HASH]/deps/foo[..].d
 
 "#]]);