[confmap] Add featuregate to use stable expansion rules

.chloggen/confmap-add-expand-featuregate-3.yaml

@@ -0,0 +1,29 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: otelcol/expandconverter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add `confmap.unifyEnvVarExpansion` feature gate to allow enabling Collector/Configuration SIG environment variable expansion rules.
+
+# One or more tracking issues or pull requests related to the change
+issues: [10391]
+
+# (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: |
+  When enabled, this feature gate will:
+  - Disable expansion of BASH-style env vars (`$FOO`)
+  - `${FOO}` will be expanded as if it was `${env:FOO}
+  See https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/rfcs/env-vars.md for more details.
+
+# 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-add-expand-featuregate.yaml

@@ -0,0 +1,29 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. otlpreceiver)
+component: confmap
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add `confmap.unifyEnvVarExpansion` feature gate to allow enabling Collector/Configuration SIG environment variable expansion rules.
+
+# One or more tracking issues or pull requests related to the change
+issues: [10259]
+
+# (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: |
+  When enabled, this feature gate will:
+    - Disable expansion of BASH-style env vars (`$FOO`)
+    - `${FOO}` will be expanded as if it was `${env:FOO}
+  See https://github.com/open-telemetry/opentelemetry-collector/blob/main/docs/rfcs/env-vars.md for more details.
+
+# 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: []

cmd/mdatagen/go.mod

@@ -32,6 +32,7 @@ require (
 	github.com/go-viper/mapstructure/v2 v2.0.0-alpha.1 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
 	github.com/google/uuid v1.6.0 // indirect
+	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
 	github.com/knadh/koanf/maps v0.1.1 // indirect
 	github.com/knadh/koanf/providers/confmap v0.1.0 // indirect
@@ -45,6 +46,7 @@ require (
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.54.0 // indirect
 	github.com/prometheus/procfs v0.15.0 // indirect
+	go.opentelemetry.io/collector/featuregate v1.9.0 // indirect
 	go.opentelemetry.io/otel/exporters/prometheus v0.49.0 // indirect
 	go.opentelemetry.io/otel/sdk v1.27.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect

config/configauth/go.mod

@@ -14,6 +14,7 @@ require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.0.0-alpha.1 // indirect
 	github.com/gogo/protobuf v1.3.2 // indirect
+	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.1 // indirect
 	github.com/knadh/koanf/providers/confmap v0.1.0 // indirect
 	github.com/knadh/koanf/v2 v2.1.1 // indirect
@@ -22,6 +23,7 @@ require (
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	go.opentelemetry.io/collector/config/configtelemetry v0.102.1 // indirect
 	go.opentelemetry.io/collector/confmap v0.102.1 // indirect
+	go.opentelemetry.io/collector/featuregate v1.9.0 // indirect
 	go.opentelemetry.io/collector/pdata v1.9.0 // indirect
 	go.opentelemetry.io/otel v1.27.0 // indirect
 	go.opentelemetry.io/otel/metric v1.27.0 // indirect
@@ -48,3 +50,5 @@ replace go.opentelemetry.io/collector/config/configtelemetry => ../configtelemet
 replace go.opentelemetry.io/collector/extension => ../../extension
 
 replace go.opentelemetry.io/collector/extension/auth => ../../extension/auth
+
+replace go.opentelemetry.io/collector/featuregate => ../../featuregate

confmap/converter/expandconverter/expand.go

@@ -5,6 +5,7 @@
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"regexp"
@@ -80,21 +81,27 @@
 func (c converter) expandEnv(s string) (string, error) {
 	var err error
 	res := os.Expand(s, func(str string) string {
+		// This allows escaping environment variable substitution via $$, e.g.
+		// - $FOO will be substituted with env var FOO
+		// - $$FOO will be replaced with $FOO
+		// - $$$FOO will be replaced with $ + substituted env var FOO
+		if str == "$" {
+			return "$"
+		}
+
 		// Matches on $VAR style environment variables
 		// in order to make sure we don't log a warning for ${VAR}
 		var regex = regexp.MustCompile(fmt.Sprintf(`\$%s`, regexp.QuoteMeta(str)))
 		if _, exists := c.loggedDeprecations[str]; !exists && regex.MatchString(s) {
+			if confmap.UseUnifiedEnvVarExpansionRules.IsEnabled() {
+				err = errors.New("$VAR expansion is not supported when feature gate confmap.unifyEnvVarExpansion is enabled")
+				return ""
+			}
 			msg := fmt.Sprintf("Variable substitution using $VAR will be deprecated in favor of ${VAR} and ${env:VAR}, please update $%s", str)
 			c.logger.Warn(msg, zap.String("variable", str))
 			c.loggedDeprecations[str] = struct{}{}
 		}
-		// This allows escaping environment variable substitution via $$, e.g.
-		// - $FOO will be substituted with env var FOO
-		// - $$FOO will be replaced with $FOO
-		// - $$$FOO will be replaced with $ + substituted env var FOO
-		if str == "$" {
-			return "$"
-		}
+
 		// For $ENV style environment variables os.Expand returns once it hits a character that isn't an underscore or
 		// an alphanumeric character - so we cannot detect those malformed environment variables.
 		// For ${ENV} style variables we can detect those kinds of env var names!

confmap/converter/expandconverter/go.mod

@@ -12,14 +12,18 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.0.0-alpha.1 // indirect
+	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.1 // indirect
 	github.com/knadh/koanf/providers/confmap v0.1.0 // indirect
 	github.com/knadh/koanf/v2 v2.1.1 // indirect
 	github.com/mitchellh/copystructure v1.2.0 // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	go.opentelemetry.io/collector/featuregate v1.9.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
 
 replace go.opentelemetry.io/collector/confmap => ../../
+
+replace go.opentelemetry.io/collector/featuregate => ../../../featuregate

confmap/go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/knadh/koanf/providers/confmap v0.1.0
 	github.com/knadh/koanf/v2 v2.1.1
 	github.com/stretchr/testify v1.9.0
+	go.opentelemetry.io/collector/featuregate v1.9.0
 	go.uber.org/goleak v1.3.0
 	go.uber.org/multierr v1.11.0
 	go.uber.org/zap v1.27.0
@@ -16,6 +17,7 @@ require (
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/mitchellh/copystructure v1.2.0 // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
@@ -25,3 +27,5 @@ retract (
 	v0.76.0 // Depends on retracted pdata v1.0.0-rc10 module, use v0.76.1
 	v0.69.0 // Release failed, use v0.69.1
 )
+
+replace go.opentelemetry.io/collector/featuregate => ../featuregate

confmap/provider/envprovider/go.mod

@@ -12,14 +12,18 @@ require (
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/go-viper/mapstructure/v2 v2.0.0-alpha.1 // indirect
+	github.com/hashicorp/go-version v1.7.0 // indirect
 	github.com/knadh/koanf/maps v0.1.1 // indirect
 	github.com/knadh/koanf/providers/confmap v0.1.0 // indirect
 	github.com/knadh/koanf/v2 v2.1.1 // indirect
 	github.com/mitchellh/copystructure v1.2.0 // indirect
 	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
+	go.opentelemetry.io/collector/featuregate v1.9.0 // indirect
 	go.uber.org/multierr v1.11.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
 
 replace go.opentelemetry.io/collector/confmap => ../../
+
+replace go.opentelemetry.io/collector/featuregate => ../../../featuregate