Rework ASSUME_PROVIDED and notes

README.md

@@ -3,6 +3,12 @@
 This openembedded layer provides the rust compiler, tools for building packages
 (cargo), and a few example projects.
 
+By default we assume that there is a local `cargo` (ie: `cargo-native`). To disable this and try to build cargo, add:
+
+    CARGO_PROVIDED = ""
+
+To a conf file (probably local.conf)
+
 ## What works:
 
  - MACHINE="beaglebone" (TARGET_SYS=arm-poky-linux-gnueabi)
@@ -13,12 +19,16 @@ This openembedded layer provides the rust compiler, tools for building packages
 
  - Probably some of the untested things
  - cargo and cargo-native (use a local package for -native)
-	- We provide .bb files for these, and they are working every
-	  now-and-then. Unfortunately, rust moves a bit too quickly for cargo
-          to keep up, and it ends up broken fairly often.
 
-	- To use a local cargo, add `ASSUME_PROVIDED = "cargo-native"` to your
+### What about cargo?:
-	  local.conf file (or use the `bitbake -I cargo-native` option)
+
+We provide .bb files for these, and they are working every now-and-then.
+Unfortunately, rust moves a bit too quickly for cargo to keep up, and it ends
+up broken fairly often.
+
+Very often we'll want newer versions of rust than cargo is able to build with.
+Thankfully, we don't need any custom cargo configuration, and can use a vanilla
+cargo binary.
 
 ## What's untested:
 

classes/cargo.bbclass

@@ -2,11 +2,6 @@ inherit rust
 
 CARGO = "cargo"
 
-# cargo & rust go out of sync rather frequently. Very often we'll want newer
-# versions of rust than cargo is able to build with. Thankfully, we don't need
-# any custom cargo configuration, and can use a vanilla cargo binary.
-#
-# We recommend setting ASSUME_PROVIDED += "cargo-native" in your local.conf
 def cargo_base_dep(d):
     deps = ""
     if not d.getVar('INHIBIT_DEFAULT_DEPS') and not d.getVar('INHIBIT_CARGO_DEP'):

conf/layer.conf

@@ -7,3 +7,8 @@ BBFILES += "${LAYERDIR}/recipes*/*/*.bb ${LAYERDIR}/recipes*/*/*.bbappend"
 BBFILE_COLLECTIONS += "rust-layer"
 BBFILE_PATTERN_rust-layer := "^${LAYERDIR}/"
 BBFILE_PRIORITY_rust-layer = "7"
+
+# cargo generally doesn't work with the latest rust. Default to using the
+# system's own cargo for cargo-native.
+CARGO_PROVIDED = "cargo-native"
+ASSUME_PROVIDED += "${CARGO_PROVIDED}"