Support variables/interpolation in o>, e>, o+e> redirect (#9747)

# Description
Fixes:  #8517
Fixes: #9246
Fixes: #9709
Relative: #9723


## About the change
Before the pr, nushell only parse redirection target as a string(through
`parse_string` call).
In the pr, I'm trying to make the value more generic(using `parse_value`
with `SyntaxShape::Any`)

And during eval stage, we guard it to only eval `String`,
`StringInterpolation`, `FullCellPath`, `FilePath`, so other type of
redirection target like `1ms` won't be permitted.

# User-Facing Changes

After the pr: redirection support something like the following:
1. `let a = "x"; cat toolkit.nu o> $a`
2. `let a = "x"; cat toolkit.nu o> $"($a).txt"`
3. `cat toolkit.nu out> ("~/a.txt" | path expand)`

crates/nu-command/tests/commands/redirection.rs

@@ -205,3 +205,62 @@ fn redirection_with_pipeline_works() {
         },
     )
 }
+
+#[test]
+fn redirect_support_variable() {
+    Playground::setup("redirect_out_support_variable", |dirs, _sandbox| {
+        let output = nu!(
+            cwd: dirs.test(),
+            "let x = 'tmp_file'; echo 'hello' out> $x; open tmp_file"
+        );
+
+        assert!(output.out.contains("hello"));
+
+        let output = nu!(
+            cwd: dirs.test(),
+            "let x = 'tmp_file'; echo 'hello' out+err> $x; open tmp_file"
+        );
+
+        assert!(output.out.contains("hello"));
+    })
+}
+
+#[test]
+fn separate_redirection_support_variable() {
+    Playground::setup(
+        "external with both stdout and stderr messages, to different file",
+        |dirs, sandbox| {
+            let script_body = r#"
+        echo message
+        echo message 1>&2
+        "#;
+            let expect_body = "message";
+
+            #[cfg(not(windows))]
+            {
+                sandbox.with_files(vec![FileWithContent("test.sh", script_body)]);
+                nu!(
+                    cwd: dirs.test(),
+                    r#"let o_f = "out.txt"; let e_f = "err.txt"; bash test.sh out> $o_f err> $e_f"#
+                );
+            }
+            #[cfg(windows)]
+            {
+                sandbox.with_files(vec![FileWithContent("test.bat", script_body)]);
+                nu!(
+                    cwd: dirs.test(),
+                    r#"let o_f = "out.txt"; let e_f = "err.txt"; cmd /D /c test.bat out> $o_f err> $e_f"#
+                );
+            }
+            // check for stdout redirection file.
+            let expected_out_file = dirs.test().join("out.txt");
+            let actual = file_contents(expected_out_file);
+            assert!(actual.contains(expect_body));
+
+            // check for stderr redirection file.
+            let expected_err_file = dirs.test().join("err.txt");
+            let actual = file_contents(expected_err_file);
+            assert!(actual.contains(expect_body));
+        },
+    )
+}

crates/nu-engine/src/eval.rs

@@ -795,7 +795,10 @@ pub fn eval_element_with_input(
             redirect_stderr,
         ),
         PipelineElement::Redirection(span, redirection, expr) => match &expr.expr {
-            Expr::String(_) => {
+            Expr::String(_)
+            | Expr::FullCellPath(_)
+            | Expr::StringInterpolation(_)
+            | Expr::Filepath(_) => {
                 let exit_code = match &mut input {
                     PipelineData::ExternalStream { exit_code, .. } => exit_code.take(),
                     _ => None,
@@ -880,7 +883,16 @@ pub fn eval_element_with_input(
             out: (out_span, out_expr),
             err: (err_span, err_expr),
         } => match (&out_expr.expr, &err_expr.expr) {
-            (Expr::String(_), Expr::String(_)) => {
+            (
+                Expr::String(_)
+                | Expr::FullCellPath(_)
+                | Expr::StringInterpolation(_)
+                | Expr::Filepath(_),
+                Expr::String(_)
+                | Expr::FullCellPath(_)
+                | Expr::StringInterpolation(_)
+                | Expr::Filepath(_),
+            ) => {
                 if let Some(save_command) = engine_state.find_decl(b"save", &[]) {
                     let exit_code = match &mut input {
                         PipelineData::ExternalStream { exit_code, .. } => exit_code.take(),

crates/nu-parser/src/parser.rs

@@ -5522,8 +5522,7 @@ pub fn parse_pipeline(
                     PipelineElement::Expression(*span, expr)
                 }
                 LiteElement::Redirection(span, redirection, command) => {
-                    trace!("parsing: pipeline element: redirection");
+                    let expr = parse_value(working_set, command.parts[0], &SyntaxShape::Any);
-                    let expr = parse_string(working_set, command.parts[0]);
 
                     PipelineElement::Redirection(*span, redirection.clone(), expr)
                 }
@@ -5532,9 +5531,11 @@ pub fn parse_pipeline(
                     err: (err_span, err_command),
                 } => {
                     trace!("parsing: pipeline element: separate redirection");
-                    let out_expr = parse_string(working_set, out_command.parts[0]);
+                    let out_expr =
+                        parse_value(working_set, out_command.parts[0], &SyntaxShape::Any);
 
-                    let err_expr = parse_string(working_set, err_command.parts[0]);
+                    let err_expr =
+                        parse_value(working_set, err_command.parts[0], &SyntaxShape::Any);
 
                     PipelineElement::SeparateRedirection {
                         out: (*out_span, out_expr),
@@ -5547,7 +5548,8 @@ pub fn parse_pipeline(
                 } => {
                     trace!("parsing: pipeline element: same target redirection");
                     let expr = parse_expression(working_set, &command.parts, is_subexpression);
-                    let redirect_expr = parse_string(working_set, redirect_command.parts[0]);
+                    let redirect_expr =
+                        parse_value(working_set, redirect_command.parts[0], &SyntaxShape::Any);
                     PipelineElement::SameTargetRedirection {
                         cmd: (*cmd_span, expr),
                         redirection: (*redirect_span, redirect_expr),
@@ -5636,7 +5638,8 @@ pub fn parse_pipeline(
                 trace!("parsing: pipeline element: same target redirection");
                 let expr = parse_expression(working_set, &command.parts, is_subexpression);
 
-                let redirect_expr = parse_string(working_set, redirect_cmd.parts[0]);
+                let redirect_expr =
+                    parse_value(working_set, redirect_cmd.parts[0], &SyntaxShape::Any);
 
                 Pipeline {
                     elements: vec![PipelineElement::SameTargetRedirection {