From d5477c41bfbf0e0e6fc7fcf6ce0b4cb217ebd1e5 Mon Sep 17 00:00:00 2001
From: Aidan Oldershaw <aoldershaw@pivotal.io>
Date: Mon, 26 Apr 2021 11:37:26 -0400
Subject: [PATCH] allow setting a semver constraint

Signed-off-by: Aidan Oldershaw <aoldershaw@pivotal.io>
---
 README.md         |  4 ++++
 check_test.go     | 23 ++++++++++++++++++++---
 commands/check.go | 15 ++++++++++++++-
 types.go          |  2 ++
 4 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index d00c1ea..73661d0 100644
--- a/README.md
+++ b/README.md
@@ -54,6 +54,10 @@ differences:
   would be used for tags like `1.2.3-stretch`. This is typically used *without*
   `tag` - if it is set, this value will only used for pushing, not checking.
 
+* `semver_constraint`: *Optional.* Constrain the returned semver tags according
+  to a semver constraint, e.g. `"~1.2.x"`, `">= 1.2 < 3.0.0 || >= 4.2.3"`.
+  Follows the rules outlined in https://github.com/Masterminds/semver#checking-version-constraints.
+
 * `username` and `password`: *Optional.* A username and password to use when
   authenticating to the registry. Must be specified for private repos or when
   using `put`.
diff --git a/check_test.go b/check_test.go
index b13eeca..869d26e 100644
--- a/check_test.go
+++ b/check_test.go
@@ -862,6 +862,20 @@ var _ = DescribeTable("tracking semver tags",
 			Versions: []string{"1.0.0", "1.2.1", "2.0.0"},
 		},
 	),
+	Entry("semver constraint",
+		SemverTagCheckExample{
+			Tags: map[string]string{
+				"1.0.0": "random-1",
+				"1.2.1": "random-3",
+				"1.2.2": "random-4",
+				"2.0.0": "random-5",
+				// Does not include bare tag
+				"latest": "random-6",
+			},
+			SemverConstraint: "1.2.x",
+			Versions:         []string{"1.2.1", "1.2.2"},
+		},
+	),
 	Entry("prereleases ignored by default",
 		SemverTagCheckExample{
 			Tags: map[string]string{
@@ -1109,6 +1123,8 @@ type SemverTagCheckExample struct {
 	PreReleases bool
 	Variant     string
 
+	SemverConstraint string
+
 	Repository     string
 	RegistryMirror string
 	WorkingMirror  bool
@@ -1141,9 +1157,10 @@ func (example SemverTagCheckExample) Run() {
 
 	req := resource.CheckRequest{
 		Source: resource.Source{
-			Repository:  repo.Name(),
-			PreReleases: example.PreReleases,
-			Variant:     example.Variant,
+			Repository:       repo.Name(),
+			PreReleases:      example.PreReleases,
+			Variant:          example.Variant,
+			SemverConstraint: example.SemverConstraint,
 		},
 	}
 
diff --git a/commands/check.go b/commands/check.go
index 477fb04..646ffba 100644
--- a/commands/check.go
+++ b/commands/check.go
@@ -129,6 +129,14 @@ func checkRepository(repo name.Repository, source resource.Source, from *resourc
 		})
 	}
 
+	var constraint *semver.Constraints
+	if source.SemverConstraint != "" {
+		constraint, err = semver.NewConstraint(source.SemverConstraint)
+		if err != nil {
+			return resource.CheckResponse{}, fmt.Errorf("parse semver constraint: %w", err)
+		}
+	}
+
 	for _, identifier := range tags {
 		var ver *semver.Version
 		if identifier == bareTag {
@@ -149,6 +157,11 @@ func checkRepository(repo name.Repository, source resource.Source, from *resourc
 				continue
 			}
 
+			if constraint != nil && !constraint.Check(ver) {
+				// semver constraint not met
+				continue
+			}
+
 			pre := ver.Prerelease()
 			if pre != "" {
 				// pre-releases not enabled; skip
@@ -246,7 +259,7 @@ func checkRepository(repo name.Repository, source resource.Source, from *resourc
 		digest := tagDigests[latestTag]
 
 		_, existsAsSemver := digestVersions[digest]
-		if !existsAsSemver {
+		if !existsAsSemver && constraint == nil {
 			response = append(response, resource.Version{
 				Tag:    latestTag,
 				Digest: digest,
diff --git a/types.go b/types.go
index f129697..e9aade4 100644
--- a/types.go
+++ b/types.go
@@ -80,6 +80,8 @@ type Source struct {
 	PreReleases bool   `json:"pre_releases,omitempty"`
 	Variant     string `json:"variant,omitempty"`
 
+	SemverConstraint string `json:"semver_constraint,omitempty"`
+
 	Tag Tag `json:"tag,omitempty"`
 
 	BasicCredentials