[confmap] Move confmap.unifyEnvVarExpansion to beta (#10435)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Moves confmap.unifyEnvVarExpansion to beta. This means the collector
will, by default, use the env var provider to expand `${FOO}` synatx and
will error if the expandconverter is used to expand `$FOO` syntax.

<!-- Issue number if applicable -->
#### Link to tracking issue
Related to
#10161
Related to
#8215
Related to
#7111

---------

Co-authored-by: Pablo Baeyens <[email protected]>

.chloggen/confmap-unifyEnvVarExpansion-gate-beta-2.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: otelcol
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: By default, `otelcol.NewCommand` and `otelcol.NewCommandMustSetProvider` will set the `DefaultScheme` to `env`.
+
+# One or more tracking issues or pull requests related to the change
+issues: [10435]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

.chloggen/confmap-unifyEnvVarExpansion-gate-beta.yaml

@@ -0,0 +1,25 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: breaking
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: expandconverter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: By default expandconverter will now error if it is about to expand `$FOO` syntax. Update configuration to use `${env:FOO}` instead or disable the feature gate.
+
+# One or more tracking issues or pull requests related to the change
+issues: [10435]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

confmap/converter/expandconverter/expand.go

@@ -5,7 +5,6 @@ package expandconverter // import "go.opentelemetry.io/collector/confmap/convert
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"os"
 	"regexp"
@@ -95,7 +94,7 @@ func (c converter) expandEnv(s string) (string, error) {
 		var regex = regexp.MustCompile(fmt.Sprintf(`\$%s`, regexp.QuoteMeta(str)))
 		if _, exists := c.loggedDeprecations[str]; !exists && regex.MatchString(s) {
 			if featuregates.UseUnifiedEnvVarExpansionRules.IsEnabled() {
-				err = errors.New("$VAR expansion is not supported when feature gate confmap.unifyEnvVarExpansion is enabled")
+				err = fmt.Errorf("variable substitution using $VAR has been deprecated in favor of ${VAR} and ${env:VAR} - please update $%s or temporarily disable the confmap.unifyEnvVarExpansion feature gate", str)
 				return ""
 			}
 			msg := fmt.Sprintf("Variable substitution using $VAR will be deprecated in favor of ${VAR} and ${env:VAR}, please update $%s", str)

confmap/converter/expandconverter/expand_test.go

@@ -48,6 +48,11 @@ func TestNewExpandConverter(t *testing.T) {
 
 	for _, test := range testCases {
 		t.Run(test.name, func(t *testing.T) {
+			require.NoError(t, featuregate.GlobalRegistry().Set(featuregates.UseUnifiedEnvVarExpansionRules.ID(), false))
+			t.Cleanup(func() {
+				require.NoError(t, featuregate.GlobalRegistry().Set(featuregates.UseUnifiedEnvVarExpansionRules.ID(), true))
+			})
+
 			conf, err := confmaptest.LoadConf(filepath.Join("testdata", test.name))
 			require.NoError(t, err, "Unable to get config")
 
@@ -80,7 +85,7 @@ func TestNewExpandConverter_UseUnifiedEnvVarExpansionRules(t *testing.T) {
 	require.NoError(t, err, "Unable to get config")
 
 	// Test that expanded configs are the same with the simple config with no env vars.
-	require.ErrorContains(t, createConverter().Convert(context.Background(), conf), "$VAR expansion is not supported when feature gate confmap.unifyEnvVarExpansion is enabled")
+	require.ErrorContains(t, createConverter().Convert(context.Background(), conf), "variable substitution using $VAR has been deprecated in favor of ${VAR} and ${env:VAR}")
 }
 
 func TestNewExpandConverter_EscapedMaps(t *testing.T) {

internal/featuregates/featuregates.go

@@ -6,6 +6,6 @@ package featuregates // import "go.opentelemetry.io/collector/internal/featurega
 import "go.opentelemetry.io/collector/featuregate"
 
 var UseUnifiedEnvVarExpansionRules = featuregate.GlobalRegistry().MustRegister("confmap.unifyEnvVarExpansion",
-	featuregate.StageAlpha,
+	featuregate.StageBeta,
 	featuregate.WithRegisterFromVersion("v0.103.0"),
 	featuregate.WithRegisterDescription("`${FOO}` will now be expanded as if it was `${env:FOO}` and no longer expands $ENV syntax. See https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/rfcs/env-vars.md for more details. When this feature gate is stable, expandconverter will be removed."))

otelcol/command_test.go

@@ -36,6 +36,7 @@ func TestNewCommandProgrammaticallyPassedConfig(t *testing.T) {
 	cmd := NewCommandMustSetProvider(CollectorSettings{Factories: nopFactories, ConfigProviderSettings: ConfigProviderSettings{
 		ResolverSettings: confmap.ResolverSettings{
 			ProviderFactories: []confmap.ProviderFactory{confmap.NewProviderFactory(newFailureProvider)},
+			DefaultScheme:     "file",
 		},
 	}})
 	otelRunE := cmd.RunE