fix: report bare identifier assignment as a compile error

pkg/lib/purus-core.js

@@ -39,11 +39,17 @@ function compile(source, options = {}) {
       args.push("--type", "commonjs");
     }
     args.push(tmpFile);
-    let result = execFileSync(process.execPath, [COMPILER_JS, ...args], {
-      encoding: "utf8",
-      stdio: ["pipe", "pipe", "pipe"],
-      timeout: 30000,
-    });
+    let result;
+    try {
+      result = execFileSync(process.execPath, [COMPILER_JS, ...args], {
+        encoding: "utf8",
+        stdio: ["pipe", "pipe", "pipe"],
+        timeout: 30000,
+      });
+    } catch (err) {
+      const detail = `${err.stdout || ""}${err.stderr || ""}`.trim();
+      throw new Error(detail || `Compile error: ${err.message}`);
+    }
     result = stdlib.postProcess(result);
     if (header) {
       return `// Generated by Purus ${VERSION}\n${result}`;
@@ -80,7 +86,8 @@ function check(source) {
     });
     return true;
   } catch (err) {
-    throw new Error(`Syntax error: ${err.stderr || err.message}`);
+    const detail = `${err.stdout || ""}${err.stderr || ""}`.trim();
+    throw new Error(`Syntax error: ${detail || err.message}`);
   } finally {
     try {
       fs.unlinkSync(tmpFile);

src/cmd/main/main.mbt

@@ -69,7 +69,14 @@ fn cmd_build(args : Array[String]) -> Unit {
     filtered.push(tokens[fi])
     fi += 1
   }
-  let stmts = @parser.Parser::new(filtered).parse()
+  let parser = @parser.Parser::new(filtered)
+  let stmts = parser.parse()
+  if parser.errors.length() > 0 {
+    for msg in parser.errors {
+      println("Error: " + msg)
+    }
+    @sys.exit(1)
+  }
   let header = if no_header {
     ""
   } else {
@@ -140,7 +147,14 @@ fn cmd_check(file : String) -> Unit {
     }
   }
   let tokens = @lexer.Lexer::new(src).tokenize()
-  let _stmts = @parser.Parser::new(tokens).parse()
+  let parser = @parser.Parser::new(tokens)
+  let _stmts = parser.parse()
+  if parser.errors.length() > 0 {
+    for msg in parser.errors {
+      println("Error: " + msg)
+    }
+    @sys.exit(1)
+  }
   println("OK: " + file)
 }
 

src/codegen/codegen_test.mbt

@@ -266,8 +266,11 @@ test "codegen: hyphenated ident becomes underscore" {
 
 ///|
 test "codegen: bare ident assignment is discarded" {
+  // Bare identifier assignment is a parse error (reported via Parser::errors
+  // and rejected by the CLI). The recovery AST still emits the identifier as
+  // an expression so codegen never sees the dropped assignment.
   let js = compile("x be 42")
-  assert_eq(js, "x;\n") // bare ident assignment is not supported; emits identifier as expression
+  assert_eq(js, "x;\n")
 }
 
 ///|

src/parser/parser.mbt

@@ -4,11 +4,12 @@
 pub(all) struct Parser {
   tokens : Array[@lexer.Token]
   mut pos : Int
+  errors : Array[String]
 }
 
 ///|
 pub fn Parser::new(tokens : Array[@lexer.Token]) -> Parser {
-  { tokens, pos: 0 }
+  { tokens, pos: 0, errors: [] }
 }
 
 ///|
@@ -223,7 +224,20 @@ fn Parser::parse_stmt(self : Parser) -> Stmt? {
           // Bare identifier assignment (x be val) is not supported.
           // Use const/let/var for declarations. Property and index access assignments remain valid.
           match expr {
-            Ident(_) => Some(ExprStmt(expr)) // discard; bare variable assignment is removed
+            Ident(name) => {
+              self.errors.push(
+                "bare identifier assignment ('" +
+                name +
+                " be ...') is not supported. Declare with 'const " +
+                name +
+                " be ...' or 'let " +
+                name +
+                " be ...', or use compound assignment such as '" +
+                name +
+                " add be 1'",
+              )
+              Some(ExprStmt(expr))
+            }
             _ => Some(self.maybe_postfix(Assign(expr, value)))
           }
         }

src/parser/parser_wbtest.mbt

@@ -45,13 +45,34 @@ test "parser: var declaration with string" {
 }
 
 ///|
-test "parser: bare ident assignment is discarded" {
-  let stmts = parse("x be 10")
+test "parser: bare ident assignment is a parse error" {
+  let parser = Parser::new(tokenize("x be 10"))
+  let stmts = parser.parse()
   assert_eq(stmts.length(), 1)
   match stmts[0] {
     ExprStmt(Ident(name)) => assert_eq(name, "x")
     _ => fail("expected ExprStmt(Ident) - bare assignment is not supported")
   }
+  assert_eq(parser.errors.length(), 1)
+  assert_true(parser.errors[0].contains("bare identifier assignment"))
+  assert_true(parser.errors[0].contains("'x be ...'"))
+}
+
+///|
+test "parser: bare reassignment after let is a parse error" {
+  let parser = Parser::new(tokenize("let y be 10\ny be 20"))
+  let _stmts = parser.parse()
+  assert_eq(parser.errors.length(), 1)
+  assert_true(parser.errors[0].contains("'y be ...'"))
+}
+
+///|
+test "parser: property and compound assignments report no errors" {
+  let parser = Parser::new(
+    tokenize("obj.field be 10\narr[\\0] be 1\nlet z be 0\nz add be 1"),
+  )
+  let _stmts = parser.parse()
+  assert_eq(parser.errors.length(), 0)
 }
 
 ///|