[pkg/stanza] Fix issue where add operator did not correctly compile expressions

.chloggen/pkg-stanza-fix-add.yaml

@@ -0,0 +1,27 @@
+  # Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: filelogreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix the behavior of the add operator to continue to support EXPR(env("MY_ENV_VAR")) expressions
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [26373]
+
+# (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:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# 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: []

pkg/stanza/operator/helper/expr_string.go

@@ -91,6 +91,10 @@ func (e ExprStringConfig) Build() (*ExprString, error) {
 	}, nil
 }
 
+func ExprCompile(input string) (*vm.Program, error) {
+	return expr.Compile(input, expr.AllowUndefinedVariables(), expr.Patch(&patcher{}))
+}
+
 func ExprCompileBool(input string) (*vm.Program, error) {
 	return expr.Compile(input, expr.AllowUndefinedVariables(), expr.Patch(&patcher{}), expr.AsBool())
 }

pkg/stanza/operator/transformer/add/add.go

@@ -8,7 +8,6 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/antonmedv/expr"
 	"github.com/antonmedv/expr/vm"
 	"go.uber.org/zap"
 
@@ -61,7 +60,7 @@ func (c Config) Build(logger *zap.SugaredLogger) (operator.Operator, error) {
 	exprStr := strings.TrimPrefix(strVal, "EXPR(")
 	exprStr = strings.TrimSuffix(exprStr, ")")
 
-	compiled, err := expr.Compile(exprStr, expr.AllowUndefinedVariables())
+	compiled, err := helper.ExprCompile(exprStr)
 	if err != nil {
 		return nil, fmt.Errorf("failed to compile expression '%s': %w", c.IfExpr, err)
 	}

pkg/stanza/operator/transformer/add/add_test.go

@@ -297,6 +297,24 @@ func TestProcessAndBuild(t *testing.T) {
 			},
 			false,
 		},
+		{
+			"add_expr",
+			func() *Config {
+				cfg := NewConfig()
+				cfg.Field = entry.NewAttributeField("fookey")
+				cfg.Value = "EXPR('foo_' + body.key)"
+				return cfg
+			}(),
+			newTestEntry,
+			func() *entry.Entry {
+				e := newTestEntry()
+				e.Attributes = map[string]interface{}{
+					"fookey": "foo_val",
+				}
+				return e
+			},
+			false,
+		},
 	}
 	for _, tc := range cases {
 		t.Run("BuildandProcess/"+tc.name, func(t *testing.T) {