fix(repl): do not check for unused expressions (#940)

src/cli/repl.rs

@@ -168,6 +168,7 @@ fn resolve(
     let mut config = CompileConfig::default();
     // The CLI should be moved out of the "vrl" module, and then it can use the `vector-core::compile_vrl` function which includes this automatically
     config.set_read_only_path(owned_metadata_path!("vector"), true);
+    config.disable_unused_expression_check();
 
     let program = match compile_with_state(program, stdlib_functions, state, config) {
         Ok(result) => result.program,

src/compiler/compile_config.rs

@@ -6,11 +6,21 @@ use std::{
 
 type AnyMap = HashMap<TypeId, Box<dyn Any>>;
 
-#[derive(Default)]
 pub struct CompileConfig {
     /// Custom context injected by the external environment
     custom: AnyMap,
     read_only_paths: BTreeSet<ReadOnlyPath>,
+    check_unused_expressions: bool,
+}
+
+impl Default for CompileConfig {
+    fn default() -> Self {
+        CompileConfig {
+            custom: AnyMap::default(),
+            read_only_paths: BTreeSet::default(),
+            check_unused_expressions: true,
+        }
+    }
 }
 
 impl CompileConfig {
@@ -70,6 +80,15 @@ impl CompileConfig {
         self.read_only_paths
             .insert(ReadOnlyPath { path, recursive });
     }
+
+    #[must_use]
+    pub fn unused_expression_check_enabled(&self) -> bool {
+        self.check_unused_expressions
+    }
+
+    pub fn disable_unused_expression_check(&mut self) {
+        self.check_unused_expressions = false;
+    }
 }
 
 #[derive(Debug, Clone, Ord, Eq, PartialEq, PartialOrd)]

src/compiler/mod.rs

@@ -109,16 +109,20 @@ pub fn compile_with_state(
     let ast = parse(source)
         .map_err(|err| crate::diagnostic::DiagnosticList::from(vec![Box::new(err) as Box<_>]))?;
 
+    let unused_expression_check_enabled = config.unused_expression_check_enabled();
     let result = Compiler::compile(fns, ast.clone(), state, config);
-    let unused_warnings = check_for_unused_results(&ast);
-    if unused_warnings.is_empty() {
-        result
-    } else {
-        result.map(|mut compilation_result| {
-            compilation_result.warnings.extend(unused_warnings);
-            compilation_result
-        })
+
+    if unused_expression_check_enabled {
+        let unused_warnings = check_for_unused_results(&ast);
+        if !unused_warnings.is_empty() {
+            return result.map(|mut compilation_result| {
+                compilation_result.warnings.extend(unused_warnings);
+                compilation_result
+            });
+        }
     }
+
+    result
 }
 
 /// Available VRL runtimes.