Support o>>, e>>, o+e>> to append output to an external file (#10764)

# Description
Close: #10278

This pr introduces `o>>`, `e>>`, `o+e>>` to allow redirection to append
to a file.
Examples:
```nushell
echo abc o>> a.txt
echo abc o>> a.txt
cat asdf e>> a.txt
cat asdf e>> a.txt
cat asdf o+e>> a.txt
```

~~TODO:~~
~~1. currently internal commands with `o+e>` redirect to a variable is
broken: `let x = "a.txt"; echo abc o+e> $x`, not sure when it was
introduced...~~
~~2. redirect stdout and stderr with append mode doesn't supported yet:
`cat asdf o>>a.txt e>>b.ext`~~

~~For these 2 items, I'd like to fix them in different prs.~~
Already done in this pr

crates/nu-command/src/filesystem/save.rs

@@ -1,7 +1,7 @@
 use nu_engine::current_dir;
 use nu_engine::CallExt;
 use nu_path::expand_path_with;
-use nu_protocol::ast::Call;
+use nu_protocol::ast::{Call, Expr, Expression};
 use nu_protocol::engine::{Command, EngineState, Stack};
 use nu_protocol::{
     Category, Example, PipelineData, RawStream, ShellError, Signature, Span, Spanned, SyntaxShape,
@@ -67,6 +67,24 @@ impl Command for Save {
         let append = call.has_flag("append");
         let force = call.has_flag("force");
         let progress = call.has_flag("progress");
+        let out_append = if let Some(Expression {
+            expr: Expr::Bool(out_append),
+            ..
+        }) = call.get_parser_info("out-append")
+        {
+            *out_append
+        } else {
+            false
+        };
+        let err_append = if let Some(Expression {
+            expr: Expr::Bool(err_append),
+            ..
+        }) = call.get_parser_info("err-append")
+        {
+            *err_append
+        } else {
+            false
+        };
 
         let span = call.head;
         let cwd = current_dir(engine_state, stack)?;
@@ -87,7 +105,7 @@ impl Command for Save {
         match input {
             PipelineData::ExternalStream { stdout: None, .. } => {
                 // Open files to possibly truncate them
-                let _ = get_files(&path, stderr_path.as_ref(), append, force)?;
+                let _ = get_files(&path, stderr_path.as_ref(), append, false, false, force)?;
                 Ok(PipelineData::empty())
             }
             PipelineData::ExternalStream {
@@ -95,7 +113,14 @@ impl Command for Save {
                 stderr,
                 ..
             } => {
-                let (file, stderr_file) = get_files(&path, stderr_path.as_ref(), append, force)?;
+                let (file, stderr_file) = get_files(
+                    &path,
+                    stderr_path.as_ref(),
+                    append,
+                    out_append,
+                    err_append,
+                    force,
+                )?;
 
                 // delegate a thread to redirect stderr to result.
                 let handler = stderr.map(|stderr_stream| match stderr_file {
@@ -127,7 +152,14 @@ impl Command for Save {
             PipelineData::ListStream(ls, _)
                 if raw || prepare_path(&path, append, force)?.0.extension().is_none() =>
             {
-                let (mut file, _) = get_files(&path, stderr_path.as_ref(), append, force)?;
+                let (mut file, _) = get_files(
+                    &path,
+                    stderr_path.as_ref(),
+                    append,
+                    out_append,
+                    err_append,
+                    force,
+                )?;
                 for val in ls {
                     file.write_all(&value_to_bytes(val)?)
                         .map_err(|err| ShellError::IOError(err.to_string()))?;
@@ -143,7 +175,14 @@ impl Command for Save {
                     input_to_bytes(input, Path::new(&path.item), raw, engine_state, stack, span)?;
 
                 // Only open file after successful conversion
-                let (mut file, _) = get_files(&path, stderr_path.as_ref(), append, force)?;
+                let (mut file, _) = get_files(
+                    &path,
+                    stderr_path.as_ref(),
+                    append,
+                    out_append,
+                    err_append,
+                    force,
+                )?;
 
                 file.write_all(&bytes)
                     .map_err(|err| ShellError::IOError(err.to_string()))?;
@@ -319,17 +358,19 @@ fn get_files(
     path: &Spanned<PathBuf>,
     stderr_path: Option<&Spanned<PathBuf>>,
     append: bool,
+    out_append: bool,
+    err_append: bool,
     force: bool,
 ) -> Result<(File, Option<File>), ShellError> {
     // First check both paths
-    let (path, path_span) = prepare_path(path, append, force)?;
+    let (path, path_span) = prepare_path(path, append || out_append, force)?;
     let stderr_path_and_span = stderr_path
         .as_ref()
-        .map(|stderr_path| prepare_path(stderr_path, append, force))
+        .map(|stderr_path| prepare_path(stderr_path, append || err_append, force))
         .transpose()?;
 
     // Only if both files can be used open and possibly truncate them
-    let file = open_file(path, path_span, append)?;
+    let file = open_file(path, path_span, append || out_append)?;
 
     let stderr_file = stderr_path_and_span
         .map(|(stderr_path, stderr_path_span)| {
@@ -342,7 +383,7 @@ fn get_files(
                     vec![],
                 ))
             } else {
-                open_file(stderr_path, stderr_path_span, append)
+                open_file(stderr_path, stderr_path_span, append || err_append)
             }
         })
         .transpose()?;

crates/nu-command/src/formats/from/nuon.rs

@@ -124,7 +124,7 @@ impl Command for FromNuon {
             } else {
                 match pipeline.elements.remove(0) {
                     PipelineElement::Expression(_, expression)
-                    | PipelineElement::Redirection(_, _, expression)
+                    | PipelineElement::Redirection(_, _, expression, _)
                     | PipelineElement::And(_, expression)
                     | PipelineElement::Or(_, expression)
                     | PipelineElement::SameTargetRedirection {
@@ -132,7 +132,7 @@ impl Command for FromNuon {
                         ..
                     }
                     | PipelineElement::SeparateRedirection {
-                        out: (_, expression),
+                        out: (_, expression, _),
                         ..
                     } => expression,
                 }

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

@@ -12,6 +12,14 @@ fn redirect_err() {
         );
 
         assert!(output.out.contains("asdfasdfasdf.txt"));
+
+        // check append mode
+        let output = nu!(
+                cwd: dirs.test(),
+                "cat asdfasdfasdf.txt err>> a.txt; cat a.txt"
+        );
+        let v: Vec<_> = output.out.match_indices("asdfasdfasdf.txt").collect();
+        assert_eq!(v.len(), 2);
     })
 }
 
@@ -25,6 +33,12 @@ fn redirect_err() {
         );
 
         assert!(output.out.contains("true"));
+
+        let output = nu!(
+            cwd: dirs.test(),
+            "vol missingdrive err>> a; (open a | str stats).bytes >= 32"
+        );
+        assert!(output.out.contains("true"));
     })
 }
 
@@ -39,6 +53,10 @@ fn redirect_outerr() {
         let output = nu!(cwd: dirs.test(), "cat a");
 
         assert!(output.out.contains("asdfasdfasdf.txt"));
+
+        let output = nu!(cwd: dirs.test(), "cat asdfasdfasdf.txt o+e>> a; cat a");
+        let v: Vec<_> = output.out.match_indices("asdfasdfasdf.txt").collect();
+        assert_eq!(v.len(), 2);
     })
 }
 
@@ -53,6 +71,13 @@ fn redirect_outerr() {
         let output = nu!(cwd: dirs.test(), "(open a | str stats).bytes >= 16");
 
         assert!(output.out.contains("true"));
+
+        nu!(
+            cwd: dirs.test(),
+            "vol missingdrive out+err>> a"
+        );
+        let output = nu!(cwd: dirs.test(), "(open a | str stats).bytes >= 32");
+        assert!(output.out.contains("true"));
     })
 }
 
@@ -65,6 +90,12 @@ fn redirect_out() {
         );
 
         assert!(output.out.contains("hello"));
+
+        let output = nu!(
+            cwd: dirs.test(),
+            "echo 'hello' out>> a; open a"
+        );
+        assert!(output.out.contains("hellohello"));
     })
 }
 
@@ -124,6 +155,25 @@ fn separate_redirection() {
             let expected_err_file = dirs.test().join("err.txt");
             let actual = file_contents(expected_err_file);
             assert!(actual.contains(expect_body));
+            #[cfg(not(windows))]
+            {
+                sandbox.with_files(vec![FileWithContent("test.sh", script_body)]);
+                nu!(
+                    cwd: dirs.test(),
+                    "bash test.sh out>> out.txt err>> err.txt"
+                );
+                // check for stdout redirection file.
+                let expected_out_file = dirs.test().join("out.txt");
+                let actual = file_contents(expected_out_file);
+                let v: Vec<_> = actual.match_indices("message").collect();
+                assert_eq!(v.len(), 2);
+
+                // check for stderr redirection file.
+                let expected_err_file = dirs.test().join("err.txt");
+                let actual = file_contents(expected_err_file);
+                let v: Vec<_> = actual.match_indices("message").collect();
+                assert_eq!(v.len(), 2);
+            }
         },
     )
 }
@@ -152,6 +202,21 @@ fn same_target_redirection_with_too_much_stderr_not_hang_nushell() {
         let expected_file = dirs.test().join("another_large_file.txt");
         let actual = file_contents(expected_file);
         assert_eq!(actual, format!("{large_file_body}\n"));
+
+        // not hangs in append mode either.
+        let cloned_body = large_file_body.clone();
+        large_file_body.push_str(&format!("\n{cloned_body}"));
+        nu!(
+            cwd: dirs.test(), pipeline(
+                "
+                $env.LARGE = (open --raw a_large_file.txt);
+                nu --testbin echo_env_stderr LARGE out+err>> another_large_file.txt
+                "
+            ),
+        );
+        let expected_file = dirs.test().join("another_large_file.txt");
+        let actual = file_contents(expected_file);
+        assert_eq!(actual, format!("{large_file_body}\n"));
     })
 }
 
@@ -202,6 +267,16 @@ fn redirection_with_pipeline_works() {
             let expected_out_file = dirs.test().join("out.txt");
             let actual = file_contents(expected_out_file);
             assert!(actual.contains(expect_body));
+
+            // check append mode works
+            nu!(
+                cwd: dirs.test(),
+                "bash test.sh o>> out.txt | describe"
+            );
+            let expected_out_file = dirs.test().join("out.txt");
+            let actual = file_contents(expected_out_file);
+            let v: Vec<_> = actual.match_indices("message").collect();
+            assert_eq!(v.len(), 2);
         },
     )
 }
@@ -224,6 +299,22 @@ fn redirect_support_variable() {
         let expected_out_file = dirs.test().join("tmp_file");
         let actual = file_contents(expected_out_file);
         assert!(actual.contains("hello there"));
+
+        // append mode support variable too.
+        let output = nu!(
+            cwd: dirs.test(),
+            "let x = 'tmp_file'; echo 'hello' out>> $x; open tmp_file"
+        );
+        let v: Vec<_> = output.out.match_indices("hello").collect();
+        assert_eq!(v.len(), 2);
+
+        let output = nu!(
+            cwd: dirs.test(),
+            "let x = 'tmp_file'; echo 'hello' out+err>> $x; open tmp_file"
+        );
+        // check for stdout redirection file.
+        let v: Vec<_> = output.out.match_indices("hello").collect();
+        assert_eq!(v.len(), 3);
     })
 }
 
@@ -243,7 +334,7 @@ fn separate_redirection_support_variable() {
                 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"#
+                    r#"let o_f = "out2.txt"; let e_f = "err2.txt"; bash test.sh out> $o_f err> $e_f"#
                 );
             }
             #[cfg(windows)]
@@ -251,18 +342,38 @@ fn separate_redirection_support_variable() {
                 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"#
+                    r#"let o_f = "out2.txt"; let e_f = "err2.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 expected_out_file = dirs.test().join("out2.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 expected_err_file = dirs.test().join("err2.txt");
             let actual = file_contents(expected_err_file);
             assert!(actual.contains(expect_body));
+
+            #[cfg(not(windows))]
+            {
+                sandbox.with_files(vec![FileWithContent("test.sh", script_body)]);
+                nu!(
+                    cwd: dirs.test(),
+                    r#"let o_f = "out2.txt"; let e_f = "err2.txt"; bash test.sh out>> $o_f err>> $e_f"#
+                );
+                // check for stdout redirection file.
+                let expected_out_file = dirs.test().join("out2.txt");
+                let actual = file_contents(expected_out_file);
+                let v: Vec<_> = actual.match_indices("message").collect();
+                assert_eq!(v.len(), 2);
+
+                // check for stderr redirection file.
+                let expected_err_file = dirs.test().join("err2.txt");
+                let actual = file_contents(expected_err_file);
+                let v: Vec<_> = actual.match_indices("message").collect();
+                assert_eq!(v.len(), 2);
+            }
         },
     )
 }