edtlib: always insert root node to the graph

[gmarull]

When we have an empty Devicetree, ie,

/dts-v1/;

/ {

};

The node's dep_ordinal is never initialized because the node graph is empty. This ends up with invalid ordinal tokens (-1) in devicetree_generated.h which in turn produce some cryptic compiler errors, see e.g.

error: pasting "dts_ord_" and "-" does not give a valid preprocessing
token
   95 | #define Z_DEVICE_DT_DEV_ID(node_id) _CONCAT(dts_ord_,
      DT_DEP_ORD(node_id))

...

include/zephyr/devicetree.h:2498:41:
note: in expansion of macro 'DT_FOREACH_OKAY_HELPER'
 2498 | #define DT_FOREACH_STATUS_OKAY_NODE(fn)
      DT_FOREACH_OKAY_HELPER(fn)
            |
	    ^~~~~~~~~~~~~~~~~~~~~~
include/zephyr/device.h:1022:1:
note: in expansion of macro 'DT_FOREACH_STATUS_OKAY_NODE'
     1022 |
	  DT_FOREACH_STATUS_OKAY_NODE(Z_MAYBE_DEVICE_DECLARE_INTERNAL)

(devicetree_generated.h)

...
 #define DT_N_ORD -1
 #define DT_N_ORD_STR_SORTABLE 000-1
...

This patch makes sure root node is always inserted (without any target)
so that it gets initialized later.

Discovered as part of
#63696

Fixes #63808

[fabiobaltieri]

Neat!

[57300]

I disagree with this workaround, because it can hide real issues, like #58501.

The node's dep_ordinal is never initialized because the node graph is empty.

I don't think this should be the case. If the root node exists, then the graph should be non-empty. The problem is that edtlib always adds nodes in pairs, via add_edge(). A better solution would be to always add the root node to the graph. Then, ordinal 0 will be assigned normally.

[gmarull]

I disagree with this workaround, because it can hide real issues, like #58501.

The node's dep_ordinal is never initialized because the node graph is empty.

I don't think this should be the case. If the root node exists, then the graph should be non-empty. The problem is that edtlib always adds nodes in pairs, via add_edge(). A better solution would be to always add the root node to the graph. Then, ordinal 0 will be assigned normally.

good point, please check latest revision.

[57300]

Thanks, LGTM

[mbolivar-ampere]

This got merged before I had a chance to review, but LGTM