Add a dependency debugging directory.

cmd/depprobcheck/README.md

@@ -0,0 +1,152 @@
+# A TEST PROGRAM
+
+Edit this to see what builds in various combinations of cli-runtime
+and kube-openapi.
+
+####
+
+A recent in change in kube-openapi
+
+    https://github.com/kubernetes/kube-openapi/pull/234
+
+means that anyone depending on
+
+    k8s.io/cli-runtime@v0.20.4
+   
+and _any other package that imports kube-openapi_ (e.g. kyaml)
+may see a build error like
+
+   ~/go/pkg/mod/sigs.k8s.io/kustomize@v2.0.3+incompatible/pkg/transformers/config/factorycrd.go:71:47:
+   cannot use api.Schema.SchemaProps.Properties (type map[string]"k8s.io/kube-openapi/pkg/validation/spec".Schema)
+   as type myProperties in argument to looksLikeAk8sType
+
+## Why?
+
+As it happens,
+
+    k8s.io/cli-runtime@v0.20.4
+
+depends on
+
+    sigs.k8s.io/kustomize@v2.0.3+incompatible
+
+Line 71 of factorycrd.go in kustomize v2.0.3 is:
+
+	if !looksLikeAk8sType(api.Schema.SchemaProps.Properties) {
+
+The `looksLikeAk8sType` function accepts the argument
+
+    func looksLikeAk8sType(properties map[string]spec.Schema) bool {...}
+
+At the call point in line 71 the argument is
+
+    common.OpenAPIDefinition.Schema.SchemaProps.Properties
+
+The file factorycrd.go depends on
+
+    "github.com/go-openapi/spec"
+    "k8s.io/kube-openapi/pkg/common"
+
+The module sigs.k8s.io/kustomize@v2.0.3 predates Go modules.
+
+To pin its dependencies, it has a Gopkg.lock file and
+a vendor directory.  Per the lock file:
+
+    sigs.k8s.io/kustomize@v2.0.3
+    depends on "k8s.io/kube-openapi"
+    revision = "b3f03f55328800731ce03a164b80973014ecd455"
+
+Checking out this commit in the k8s.io/kube-openapi repo we see this
+
+    k8s.io/kube-openapi/pkg/common/common.go:
+    import  "github.com/go-openapi/spec"
+    ...
+    type OpenAPIDefinition struct {
+      Schema       spec.Schema 
+      Dependencies []string
+    }
+
+But per the imports in this file, `spec.Schema` lives in
+
+    github.com/go-openapi/spec
+
+The aforementioned Gopkg.lock file pins that at 
+
+    sigs.k8s.io/kustomize@v2.0.3
+    depends on "github.com/go-openapi/spec"
+    revision = "bcff419492eeeb01f76e77d2ebc714dc97b607f5"
+
+The struct is
+
+    github.com/go-openapi/spec:
+    type Schema struct {
+      VendorExtensible
+      SchemaProps
+      SwaggerSchemaProps
+      ExtraProps map[string]interface{} `json:"-"`
+    }
+
+    type SchemaProps struct {
+      Properties map[string]Schema
+    }
+
+This is a recursive type; Schema holds a map[string]Schema.
+
+All that is fine.
+
+The problem arises when we build a binary that depends on both
+kustomize v2.0.3 and, say, 
+
+    k8s.io/kube-openapi v0.0.0-20210421082810-95288971da7e
+
+This particular version of kube-openapi has a 'go.mod' file.
+
+kube-openapi/pkg/common/common.go at tag "95288..." contains:
+
+    import "k8s.io/kube-openapi/pkg/validation/spec"
+    ...
+    type OpenAPIDefinition struct {
+      Schema       spec.Schema 
+      Dependencies []string
+    }
+
+kube-openapi/pkg/validation/spec/schema.go at this tag contains:
+
+    type Schema struct {
+      VendorExtensible
+      SchemaProps
+      SwaggerSchemaProps
+      ExtraProps map[string]interface{} `json:"-"`
+   }
+
+etc. etc. as above.  The same layout as above, but in different files.
+
+So adding this new dependency means that 
+
+    factorycrd.go 
+
+is going to include a version of  "k8s.io/kube-openapi/pkg/common".
+that deals in the type
+
+    "k8s.io/kube-openapi/pkg/validation/spec".Schema
+
+but will then attempt to pass this type to older code (the func
+looksLikeAk8sType) which is looking to accept a
+
+    "github.com/go-openapi/spec".Schema
+
+It's the same type structure, but a different name so the 'linker' barfs.
+
+To avoid this problem, one has to either
+
+ * roll forward on cli-runtime -- depend on v0.21.0 or higher.
+ 
+ * or stick with v0.20.4, which means retaining consistency
+   with kustomize 2.0.3, which means depending on an older version
+   of k8s.io/kube-openapi that still depends on go-openapi/spec.
+ 
+   Fortunately you only have to go back to before PR
+   https://github.com/kubernetes/kube-openapi/pull/234
+
+   E.g. depend on k8s.io/kube-openapi v0.0.0-20210323165736-1a6458611d18
+