fix(config): Replace environment variables if existing but empty (#13570)

(cherry picked from commit 1dd45b1)

Author: srebhan

config/config.go

@@ -858,8 +858,8 @@ func removeComments(contents []byte) ([]byte, error) {
 func substituteEnvironment(contents []byte, oldReplacementBehavior bool) ([]byte, error) {
 	options := []template.Option{
 		template.WithReplacementFunction(func(s string, m template.Mapping, cfg *template.Config) (string, error) {
-			result, err := template.DefaultReplacementFunc(s, m, cfg)
-			if err == nil && result == "" {
+			result, applied, err := template.DefaultReplacementAppliedFunc(s, m, cfg)
+			if err == nil && !applied {
 				// Keep undeclared environment-variable patterns to reproduce
 				// pre-v1.27 behavior
 				return s, nil

config/internal_test.go

@@ -55,6 +55,14 @@ func TestEnvironmentSubstitution(t *testing.T) {
 			contents: "Env var ${MY_VAR} is set, with $MY_VAR syntax and default on this ${MY_VAR1:-Substituted}, no default on this ${MY_VAR2:-NoDefault}",
 			expected: "Env var VALUE is set, with VALUE syntax and default on this Substituted, no default on this VALUE2",
 		},
+		{
+			name: "empty but set",
+			setEnv: func(t *testing.T) {
+				t.Setenv("EMPTY", "")
+			},
+			contents: "Contains ${EMPTY} nothing",
+			expected: "Contains  nothing",
+		},
 		{
 			name:     "Default has special chars",
 			contents: `Not recommended but supported ${MY_VAR:-Default with special chars Supported#$\"}`,
@@ -181,12 +189,18 @@ func TestEnvironmentSubstitutionOldBehavior(t *testing.T) {
 			contents: `${1}`,
 			expected: `${1}`,
 		},
+		{
+			name:     "empty but set",
+			contents: "Contains ${EMPTY} nothing",
+			expected: "Contains  nothing",
+		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			t.Setenv("VAR", "foobar")
 			t.Setenv("FALLBACK", "default")
+			t.Setenv("EMPTY", "")
 			actual, err := substituteEnvironment([]byte(tt.contents), true)
 			require.NoError(t, err)
 			require.EqualValues(t, tt.expected, string(actual))

go.mod

@@ -55,7 +55,7 @@ require (
 	github.com/caio/go-tdigest v3.1.0+incompatible
 	github.com/cisco-ie/nx-telemetry-proto v0.0.0-20230117155933-f64c045c77df
 	github.com/clarify/clarify-go v0.2.4
-	github.com/compose-spec/compose-go v1.15.0
+	github.com/compose-spec/compose-go v1.16.0
 	github.com/coocood/freecache v1.2.3
 	github.com/coreos/go-semver v0.3.1
 	github.com/coreos/go-systemd v0.0.0-20190719114852-fd7a80b32e1f

go.sum

@@ -388,8 +388,8 @@ github.com/cncf/xds/go v0.0.0-20211001041855-01bcc9b48dfe/go.mod h1:eXthEFrGJvWH
 github.com/cncf/xds/go v0.0.0-20211011173535-cb28da3451f1/go.mod h1:eXthEFrGJvWHgFFCl3hGmgk+/aYT6PnTQLykKQRLhEs=
 github.com/cockroachdb/apd v1.1.0 h1:3LFP3629v+1aKXU5Q37mxmRxX/pIu1nijXydLShEq5I=
 github.com/cockroachdb/apd v1.1.0/go.mod h1:8Sl8LxpKi29FqWXR16WEFZRNSz3SoPzUzeMeY4+DwBQ=
-github.com/compose-spec/compose-go v1.15.0 h1:rv3TTgbS3U4Y8sRTngrcxDmpbz+fq26wTqHculSCi6s=
-github.com/compose-spec/compose-go v1.15.0/go.mod h1:3yngGBGfls6FHGQsg4B1z6gz8ej9SOvmAJtxCwgbcnc=
+github.com/compose-spec/compose-go v1.16.0 h1:HYk4uYWXgArHh6NG+WE4yGYayOXw+hjqJ+eJxpjWWjk=
+github.com/compose-spec/compose-go v1.16.0/go.mod h1:3yngGBGfls6FHGQsg4B1z6gz8ej9SOvmAJtxCwgbcnc=
 github.com/containerd/console v1.0.3/go.mod h1:7LqA/THxQ86k76b8c/EMSiaJ3h1eZkMkXar0TQ1gf3U=
 github.com/containerd/containerd v1.6.18 h1:qZbsLvmyu+Vlty0/Ex5xc0z2YtKpIsb5n45mAMI+2Ns=
 github.com/containerd/containerd v1.6.18/go.mod h1:1RdCUu95+gc2v9t3IL+zIlpClSmew7/0YS8O5eQZrOw=