Manifest working copy RFC (#19)

rfcs/manifest-working-copy.md

@@ -0,0 +1,33 @@
+# Always use the working copy for the manifest
+
+## Summary
+
+Instead of defaulting to building a manifest using what's in the git HEAD,
+unconditionally use what's in the working copy.
+
+## Details
+
+`./wpt manifest` supports two modes, the default (based on the `git` tree at
+HEAD) and `--work` (which uses the working copy). We supported the former mode
+mostly as a trivial performance optimization, though I believe it is now
+slower.
+
+Many people find the (default) `git` behaviour confusing (adding a new test
+won't be runnable till it's been committed, for example), and it's not clear it
+gives much in the way of benefits.
+
+We should drop support for the `git` behaviour and always use the working copy
+behaviour.
+
+We should, however, amend the working copy behaviour to, if possible, call `git
+ls-tree` (or similar) to get object IDs without having to read & hash them
+ourselves.
+
+## Risks
+
+This could make manifest generation much slower for people who have large
+numbers of extra files in their working copy.
+
+We will generate manifest items for items ignored in non-root ignore files
+(https://github.com/web-platform-tests/wpt/issues/7206), which e.g. if the CSS
+build system has been run could be tens of thousands of extra test files.