Add more tests for vector variable expansion

Update the error message to make it more clear. Also add compile_fail
tests to ensure invalid syntax are rejected.

Note rust-analyzer may still report false errors, as a workaround we can
disable the errors by adding below config:
`"rust-analyzer.diagnostics.disabled": ["macro-error"]`

Author: tao-guo

macros/src/lexer.rs

@@ -418,7 +418,10 @@ impl Lexer {
                         self.extend_last_arg(quote!(#var.as_os_str()));
                     } else {
                         if !self.last_arg_str.is_empty() {
-                            abort!(span, "vector variable can only be used alone");
+                            abort!(
+                                span,
+                                "vector variable cannot have content immediately before it"
+                            );
                         }
                         self.args.push(ParseArg::ArgVec(quote!(#var)));
                     }

macros/src/lib.rs

@@ -56,6 +56,28 @@
 //! run_fun!(echo "${msg 0}");
 //! ```
 //!
+//! ### Invalid vector variable syntax
+//!
+//! Vector variables cannot have text immediately before them:
+//! ```compile_fail
+//! # use cmd_lib::*;
+//! let opts = ["-a", "-f"];
+//! run_cmd!(ls xxx$[opts]);
+//! ```
+//!
+//! ```compile_fail
+//! # use cmd_lib::*;
+//! let msg = "hello";
+//! let opts = ["-a", "-f"];
+//! run_cmd!(ls $msg$[opts]);
+//! ```
+//!
+//! ```compile_fail
+//! # use cmd_lib::*;
+//! let opts = ["-a", "-f"];
+//! run_cmd!(echo$[opts]);
+//! ```
+//!
 //! ### Invalid redirect syntax
 //!
 //! Invalid redirect operator spacing:

tests/test_macros.rs

@@ -372,3 +372,9 @@ fn test_empty_arg() {
 fn test_env_var_with_equal_sign() {
     assert!(run_cmd!(A="-c B=c" echo).is_ok());
 }
+
+#[test]
+fn test_vector_variable() {
+    let opts = ["-n", "hello"];
+    assert!(run_cmd!(echo $[opts]).is_ok())
+}