feat: add metadata support to set_semantic_meaning (#17730)

The `set_semantic_meaning` function didn't support setting meanings that
point to metadata. This will be needed when log namespacing is enabled.

lib/vector-vrl/functions/src/set_semantic_meaning.rs

@@ -1,14 +1,14 @@
 use std::collections::BTreeMap;
 use std::ops::{Deref, DerefMut};
 use vrl::diagnostic::Label;
-use vrl::path::OwnedValuePath;
+use vrl::path::{OwnedTargetPath, PathPrefix};
 use vrl::prelude::*;
 
 #[derive(Debug, Default, Clone)]
-pub struct MeaningList(pub BTreeMap<String, OwnedValuePath>);
+pub struct MeaningList(pub BTreeMap<String, OwnedTargetPath>);
 
 impl Deref for MeaningList {
-    type Target = BTreeMap<String, OwnedValuePath>;
+    type Target = BTreeMap<String, OwnedTargetPath>;
 
     fn deref(&self) -> &Self::Target {
         &self.0
@@ -68,36 +68,41 @@ impl Function for SetSemanticMeaning {
             .expect("meaning not bytes")
             .into_owned();
 
-        // Semantic meaning can only be assigned to external fields.
-        if !query.is_external() {
+        let path = if let Some(path) = query.external_path() {
+            path
+        } else {
+            // Semantic meaning can only be assigned to external fields.
             let mut labels = vec![Label::primary(
-                "the target of this semantic meaning is non-external",
+                "this path must point to an event or metadata",
                 span,
             )];
 
             if let Some(variable) = query.as_variable() {
                 labels.push(Label::context(
-                    format!("maybe you meant \".{}\"?", variable.ident()),
+                    format!(
+                        "maybe you meant \".{}\" or \"%{}\"?",
+                        variable.ident(),
+                        variable.ident()
+                    ),
                     span,
                 ));
             }
 
             let error = ExpressionError::Error {
-                message: "semantic meaning defined for non-external target".to_owned(),
+                message: "semantic meaning is not valid for local variables".to_owned(),
                 labels,
                 notes: vec![],
             };
 
             return Err(Box::new(error) as Box<dyn DiagnosticMessage>);
-        }
-
-        let path = query.path().clone();
+        };
 
-        let exists = state
-            .external
-            .target_kind()
-            .at_path(&path)
-            .contains_any_defined();
+        let exists = match path.prefix {
+            PathPrefix::Event => state.external.target_kind(),
+            PathPrefix::Metadata => state.external.metadata_kind(),
+        }
+        .at_path(&path.path)
+        .contains_any_defined();
 
         // Reject assigning meaning to non-existing field.
         if !exists {

src/transforms/remap.rs

@@ -9,7 +9,7 @@ use std::{
 
 use codecs::MetricTagValues;
 use lookup::lookup_v2::{parse_value_path, ValuePath};
-use lookup::{metadata_path, owned_value_path, path, OwnedTargetPath, PathPrefix};
+use lookup::{metadata_path, owned_value_path, path, PathPrefix};
 use snafu::{ResultExt, Snafu};
 use vector_common::TimeZone;
 use vector_config::configurable_component;
@@ -274,7 +274,7 @@ impl TransformConfig for RemapConfig {
                     // Apply any semantic meanings set in the VRL program
                     for (id, path) in meaning {
                         // currently only event paths are supported
-                        new_type_def = new_type_def.with_meaning(OwnedTargetPath::event(path), &id);
+                        new_type_def = new_type_def.with_meaning(path, &id);
                     }
                     new_type_def
                 })