Prevent circular dependencies in $extends

roadmap.md

@@ -6,12 +6,18 @@
 
 ### Major
 
-- Un-exclude kicad8 template during default kicad version switch!
+- Straightforward-ize `extends` behaviour for tagging (see #129)
+- Un-exclude kicad8 template from coverage during default kicad version switch!
 - Merge, generalize, uniform-ize and externalize footprints!
     - onnx-like incremental opset versioning
     - Template for creating them, built-in variables they can use, documentation, external links, etc.
         - Add access to whole set of points + filtering logic, so they can implement their own connection logic as well maybe (see daisy chaining)
+        - Maybe ordering for the filter (so every instance can know that it really is the next in line)
+        - Add `chain` to footprint API similarly to how `local_net` behaves, only for daisy chaining
+        - Also, rename `local_net` to `local`, probably
     - Also considering how (or, on which layer) they define their silks, universal mirroring behaviour (see ixy/xy/sxy note), etc.
+    - When breaking anyway, remove a lot of footprints from built-in status
+        - And make sure the external infrastructure + bundling support is there to make up for it
 
 ### Minor
 

src/prepare.js

@@ -69,11 +69,12 @@ exports.inherit = config => traverse(config, config, [], (target, key, val, root
         const list = [val]
         while (candidates.length) {
             const path = candidates.shift()
-            const other = u.deepcopy(u.deep(root, path))
+            const other = u.deep(root, path)
             a.assert(other, `"${path}" (reached from "${breadcrumbs.join('.')}.$extends") does not name a valid inheritance target!`)
             let parents = other.$extends || []
             if (a.type(parents)() !== 'array') parents = [parents]
             candidates = candidates.concat(parents)
+            a.assert(!list.includes(other), `"${path}" (reached from "${breadcrumbs.join('.')}.$extends") leads to a circular dependency!`)
             list.unshift(other)
         }
         val = extend.apply(null, list)

test/cli/bundle/reference/pcbs/custom_template.kicad_pcb

@@ -1 +1 @@
-Custom template override. The secret is 42. MakerJS is 0.17.0. Ergogen is 4.0.5.
+Custom template override. The secret is 42. MakerJS is loaded. Ergogen is loaded.

test/fixtures/bundle/templates/custom_template.js

@@ -4,6 +4,6 @@ const version = require('package.json').version
 module.exports = {
     convert_outline: () => {},
     body: params => {
-        return `Custom template override. The secret is ${params.custom.secret}. MakerJS is ${m.version}. Ergogen is ${version}.`
+        return `Custom template override. The secret is ${params.custom.secret}. MakerJS is ${m.version.length ? 'loaded' : ''}. Ergogen is ${version.length ? 'loaded' : ''}.`
     }
 }

test/unit/prepare.js

@@ -61,6 +61,12 @@ describe('Prepare', function() {
             y: 2,
             z: 3
         })
+        // should be able to detect circular dependencies and error out
+        p.inherit.bind(this, {
+            a: {
+                $extends: 'a'
+            }
+        }).should.throw('circular dependency')
     })
 
     it('parameterize', function() {