Pipeline operators: && and || (#7448)

# Description

We got some feedback from folks used to other shells that `try/catch`
isn't quite as convenient as things like `||`. This PR adds `&&` as a
synonym for `;` and `||` as equivalent to what `try/catch` would do.

# User-Facing Changes

Adds `&&` and `||` pipeline operators.

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-cli/src/completions/completer.rs

@@ -127,7 +127,6 @@ impl NuCompleter {
                 match pipeline_element {
                     PipelineElement::Expression(_, expr)
                     | PipelineElement::Redirection(_, _, expr)
-                    | PipelineElement::And(_, expr)
                     | PipelineElement::Or(_, expr) => {
                         let flattened: Vec<_> = flatten_expression(&working_set, &expr);
                         let span_offset: usize = alias_offset.iter().sum();

crates/nu-cli/src/syntax_highlight.rs

@@ -232,7 +232,6 @@ fn find_matching_block_end_in_block(
             match e {
                 PipelineElement::Expression(_, e)
                 | PipelineElement::Redirection(_, _, e)
-                | PipelineElement::And(_, e)
                 | PipelineElement::Or(_, e) => {
                     if e.span.contains(global_cursor_offset) {
                         if let Some(pos) = find_matching_block_end_in_expr(

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

@@ -146,7 +146,6 @@ impl Command for FromNuon {
                 match pipeline.elements.remove(0) {
                     PipelineElement::Expression(_, expression)
                     | PipelineElement::Redirection(_, _, expression)
-                    | PipelineElement::And(_, expression)
                     | PipelineElement::Or(_, expression) => expression,
                 }
             }

crates/nu-engine/src/eval.rs

@@ -789,14 +789,16 @@ pub fn eval_element_with_input(
     redirect_stderr: bool,
 ) -> Result<(PipelineData, bool), ShellError> {
     match element {
-        PipelineElement::Expression(_, expr) => eval_expression_with_input(
+        PipelineElement::Expression(_, expr) | PipelineElement::Or(_, expr) => {
+            eval_expression_with_input(
                 engine_state,
                 stack,
                 expr,
                 input,
                 redirect_stdout,
                 redirect_stderr,
-        ),
+            )
+        }
         PipelineElement::Redirection(span, redirection, expr) => match &expr.expr {
             Expr::String(_) => {
                 let input = match (redirection, input) {
@@ -903,22 +905,6 @@ pub fn eval_element_with_input(
             }
             _ => Err(ShellError::CommandNotFound(*span)),
         },
-        PipelineElement::And(_, expr) => eval_expression_with_input(
-            engine_state,
-            stack,
-            expr,
-            input,
-            redirect_stdout,
-            redirect_stderr,
-        ),
-        PipelineElement::Or(_, expr) => eval_expression_with_input(
-            engine_state,
-            stack,
-            expr,
-            input,
-            redirect_stdout,
-            redirect_stderr,
-        ),
     }
 }
 
@@ -952,10 +938,16 @@ pub fn eval_block(
     redirect_stderr: bool,
 ) -> Result<PipelineData, ShellError> {
     let num_pipelines = block.len();
-    for (pipeline_idx, pipeline) in block.pipelines.iter().enumerate() {
+    let mut pipeline_idx = 0;
+
+    while pipeline_idx < block.pipelines.len() {
+        let pipeline = &block.pipelines[pipeline_idx];
+
         let mut i = 0;
 
-        while i < pipeline.elements.len() {
+        let mut last_element_is_pipeline_or = false;
+
+        while i < pipeline.elements.len() && !last_element_is_pipeline_or {
             let redirect_stderr = redirect_stderr
                 || ((i < pipeline.elements.len() - 1)
                     && (matches!(
@@ -964,6 +956,8 @@ pub fn eval_block(
                             | PipelineElement::Redirection(_, Redirection::StdoutAndStderr, _)
                     )));
 
+            last_element_is_pipeline_or = matches!(&pipeline.elements[i], PipelineElement::Or(..));
+
             // if eval internal command failed, it can just make early return with `Err(ShellError)`.
             let eval_result = eval_element_with_input(
                 engine_state,
@@ -990,10 +984,16 @@ pub fn eval_block(
                     // don't return `Err(ShellError)`, so nushell wouldn't show extra error message.
                 }
                 (Err(error), true) => input = PipelineData::Value(Value::Error { error }, None),
+                (output, false) if last_element_is_pipeline_or => match output {
+                    Ok(output) => {
+                        input = output.0;
+                    }
+                    Err(error) => input = PipelineData::Value(Value::Error { error }, None),
+                },
                 (output, false) => {
                     let output = output?;
                     input = output.0;
-                    // external command may runs to failed
+                    // external command may have failed
                     // make early return so remaining commands will not be executed.
                     // don't return `Err(ShellError)`, so nushell wouldn't show extra error message.
                     if output.1 {
@@ -1006,6 +1006,40 @@ pub fn eval_block(
         }
 
         if pipeline_idx < (num_pipelines) - 1 {
+            if last_element_is_pipeline_or {
+                let input_is_error = matches!(input, PipelineData::Value(Value::Error { .. }, ..));
+
+                let result =
+                    drain_and_print(engine_state, stack, input, redirect_stdout, redirect_stderr);
+
+                let last_exit_code = stack.last_exit_code(engine_state).unwrap_or(0);
+
+                if last_exit_code == 0 && result.is_ok() && !input_is_error {
+                    // Skip the next pipeline ot run because this pipeline was successful and the
+                    // user used the `a || b` connector
+                    pipeline_idx += 1;
+                }
+                input = PipelineData::empty()
+            } else {
+                drain_and_print(engine_state, stack, input, redirect_stdout, redirect_stderr)?;
+
+                input = PipelineData::empty()
+            }
+        }
+
+        pipeline_idx += 1;
+    }
+
+    Ok(input)
+}
+
+fn drain_and_print(
+    engine_state: &EngineState,
+    stack: &mut Stack,
+    mut input: PipelineData,
+    redirect_stdout: bool,
+    redirect_stderr: bool,
+) -> Result<(), ShellError> {
     match input {
         PipelineData::Value(Value::Nothing { .. }, ..) => {}
         PipelineData::ExternalStream {
@@ -1059,12 +1093,8 @@ pub fn eval_block(
                             redirect_stderr,
                         )?;
                     } else {
-                                let table = table.run(
+                        let table =
-                                    engine_state,
+                            table.run(engine_state, stack, &Call::new(Span::new(0, 0)), input)?;
-                                    stack,
-                                    &Call::new(Span::new(0, 0)),
-                                    input,
-                                )?;
 
                         print_or_return(table, config)?;
                     }
@@ -1076,11 +1106,7 @@ pub fn eval_block(
         }
     }
 
-            input = PipelineData::empty()
+    Ok(())
-        }
-    }
-
-    Ok(input)
 }
 
 fn print_or_return(pipeline_data: PipelineData, config: &Config) -> Result<(), ShellError> {

crates/nu-parser/src/flatten.rs

@@ -455,14 +455,10 @@ pub fn flatten_pipeline_element(
             output.append(&mut flatten_expression(working_set, expr));
             output
         }
-        PipelineElement::And(span, expr) => {
-            let mut output = vec![(*span, FlatShape::And)];
-            output.append(&mut flatten_expression(working_set, expr));
-            output
-        }
         PipelineElement::Or(span, expr) => {
-            let mut output = vec![(*span, FlatShape::Or)];
+            let mut output = vec![];
             output.append(&mut flatten_expression(working_set, expr));
+            output.push((*span, FlatShape::Or));
             output
         }
     }

crates/nu-parser/src/lex.rs

@@ -7,6 +7,7 @@ pub enum TokenContents {
     Comment,
     Pipe,
     PipePipe,
+    AndAnd,
     Semicolon,
     OutGreaterThan,
     ErrGreaterThan,
@@ -254,10 +255,10 @@ pub fn lex_item(
         ),
         b"&&" => (
             Token {
-                contents: TokenContents::Item,
+                contents: TokenContents::AndAnd,
                 span,
             },
-            Some(ParseError::ShellAndAnd(span)),
+            None,
         ),
         b"2>" => (
             Token {

crates/nu-parser/src/parse_keywords.rs

@@ -1420,7 +1420,9 @@ pub fn parse_module_block(
 
                         pipeline
                     }
-                    LiteElement::Redirection(_, _, command) => garbage_pipeline(&command.parts),
+                    LiteElement::Redirection(_, _, command) | LiteElement::Or(_, command) => {
+                        garbage_pipeline(&command.parts)
+                    }
                 }
             } else {
                 error = Some(ParseError::Expected("not a pipeline".into(), span));

crates/nu-parser/src/parser.rs

@@ -1223,6 +1223,7 @@ fn parse_binary_with_base(
                     }
                     TokenContents::Pipe
                     | TokenContents::PipePipe
+                    | TokenContents::AndAnd
                     | TokenContents::OutGreaterThan
                     | TokenContents::ErrGreaterThan
                     | TokenContents::OutErrGreaterThan => {
@@ -3804,7 +3805,9 @@ pub fn parse_table_expression(
         }
         _ => {
             match &output.block[0].commands[0] {
-                LiteElement::Command(_, command) | LiteElement::Redirection(_, _, command) => {
+                LiteElement::Command(_, command)
+                | LiteElement::Redirection(_, _, command)
+                | LiteElement::Or(_, command) => {
                     let mut table_headers = vec![];
 
                     let (headers, err) = parse_value(
@@ -3825,7 +3828,8 @@ pub fn parse_table_expression(
 
                     match &output.block[1].commands[0] {
                         LiteElement::Command(_, command)
-                        | LiteElement::Redirection(_, _, command) => {
+                        | LiteElement::Redirection(_, _, command)
+                        | LiteElement::Or(_, command) => {
                             let mut rows = vec![];
                             for part in &command.parts {
                                 let (values, err) = parse_value(
@@ -5282,7 +5286,9 @@ pub fn parse_block(
     for pipeline in &lite_block.block {
         if pipeline.commands.len() == 1 {
             match &pipeline.commands[0] {
-                LiteElement::Command(_, command) | LiteElement::Redirection(_, _, command) => {
+                LiteElement::Command(_, command)
+                | LiteElement::Redirection(_, _, command)
+                | LiteElement::Or(_, command) => {
                     if let Some(err) =
                         parse_def_predecl(working_set, &command.parts, expand_aliases_denylist)
                     {
@@ -5319,6 +5325,21 @@ pub fn parse_block(
 
                             PipelineElement::Expression(*span, expr)
                         }
+                        LiteElement::Or(span, command) => {
+                            let (expr, err) = parse_expression(
+                                working_set,
+                                &command.parts,
+                                expand_aliases_denylist,
+                                is_subexpression,
+                            );
+                            working_set.type_scope.add_type(expr.ty.clone());
+
+                            if error.is_none() {
+                                error = err;
+                            }
+
+                            PipelineElement::Or(*span, expr)
+                        }
                         LiteElement::Redirection(span, redirection, command) => {
                             trace!("parsing: pipeline element: redirection");
                             let (expr, err) = parse_string(
@@ -5354,8 +5375,16 @@ pub fn parse_block(
 
                 Pipeline { elements: output }
             } else {
-                match &pipeline.commands[0] {
+                let (mut pipeline, err) = match &pipeline.commands[0] {
                     LiteElement::Command(_, command) | LiteElement::Redirection(_, _, command) => {
+                        parse_builtin_commands(
+                            working_set,
+                            command,
+                            expand_aliases_denylist,
+                            is_subexpression,
+                        )
+                    }
+                    LiteElement::Or(span, command) => {
                         let (mut pipeline, err) = parse_builtin_commands(
                             working_set,
                             command,
@@ -5363,10 +5392,17 @@ pub fn parse_block(
                             is_subexpression,
                         );
 
+                        if let PipelineElement::Expression(_, expr) = &pipeline.elements[0] {
+                            pipeline.elements[0] = PipelineElement::Or(*span, expr.clone())
+                        }
+
+                        (pipeline, err)
+                    }
+                };
+
                 if idx == 0 {
                     if let Some(let_decl_id) = working_set.find_decl(b"let", &Type::Any) {
-                                if let Some(let_env_decl_id) =
+                        if let Some(let_env_decl_id) = working_set.find_decl(b"let-env", &Type::Any)
-                                    working_set.find_decl(b"let-env", &Type::Any)
                         {
                             for element in pipeline.elements.iter_mut() {
                                 if let PipelineElement::Expression(
@@ -5397,14 +5433,11 @@ pub fn parse_block(
                                     } else if element.has_in_variable(working_set)
                                         && !is_subexpression
                                     {
-                                                *element =
+                                        *element = wrap_element_with_collect(working_set, element);
-                                                    wrap_element_with_collect(working_set, element);
                                     }
-                                        } else if element.has_in_variable(working_set)
+                                } else if element.has_in_variable(working_set) && !is_subexpression
-                                            && !is_subexpression
                                 {
-                                            *element =
+                                    *element = wrap_element_with_collect(working_set, element);
-                                                wrap_element_with_collect(working_set, element);
                                 }
                             }
                         }
@@ -5417,8 +5450,6 @@ pub fn parse_block(
 
                 pipeline
             }
-                }
-            }
         })
         .into();
 
@@ -5494,7 +5525,6 @@ pub fn discover_captures_in_pipeline_element(
     match element {
         PipelineElement::Expression(_, expression)
         | PipelineElement::Redirection(_, _, expression)
-        | PipelineElement::And(_, expression)
         | PipelineElement::Or(_, expression) => {
             discover_captures_in_expr(working_set, expression, seen, seen_blocks)
         }
@@ -5755,9 +5785,6 @@ fn wrap_element_with_collect(
                 wrap_expr_with_collect(working_set, expression),
             )
         }
-        PipelineElement::And(span, expression) => {
-            PipelineElement::And(*span, wrap_expr_with_collect(working_set, expression))
-        }
         PipelineElement::Or(span, expression) => {
             PipelineElement::Or(*span, wrap_expr_with_collect(working_set, expression))
         }
@@ -5861,6 +5888,7 @@ impl LiteCommand {
 pub enum LiteElement {
     Command(Option<Span>, LiteCommand),
     Redirection(Span, Redirection, LiteCommand),
+    Or(Span, LiteCommand),
 }
 
 #[derive(Debug)]
@@ -5929,15 +5957,8 @@ pub fn lite_parse(tokens: &[Token]) -> (LiteBlock, Option<ParseError>) {
 
     let mut curr_comment: Option<Vec<Span>> = None;
 
-    let mut error = None;
-
     for token in tokens.iter() {
         match &token.contents {
-            TokenContents::PipePipe => {
-                error = error.or(Some(ParseError::ShellOrOr(token.span)));
-                curr_command.push(token.span);
-                last_token = TokenContents::Item;
-            }
             TokenContents::Item => {
                 // If we have a comment, go ahead and attach it
                 if let Some(curr_comment) = curr_comment.take() {
@@ -6073,7 +6094,25 @@ pub fn lite_parse(tokens: &[Token]) -> (LiteBlock, Option<ParseError>) {
 
                 last_token = TokenContents::Eol;
             }
-            TokenContents::Semicolon => {
+            TokenContents::PipePipe => {
+                // Different to redirection, for PipePipe, we'll wrap the current command
+                // in an "Or". This lets us know during eval that it's the current command
+                // whose error will be ignored rather than having to look ahead in the pipeline
+                if !curr_command.is_empty() {
+                    curr_pipeline.push(LiteElement::Or(token.span, curr_command));
+                    curr_command = LiteCommand::new();
+                }
+                if !curr_pipeline.is_empty() {
+                    block.push(curr_pipeline);
+
+                    curr_pipeline = LitePipeline::new();
+                    last_connector = TokenContents::Pipe;
+                    last_connector_span = None;
+                }
+
+                last_token = TokenContents::PipePipe;
+            }
+            TokenContents::Semicolon | TokenContents::AndAnd => {
                 if !curr_command.is_empty() {
                     match last_connector {
                         TokenContents::OutGreaterThan => {
@@ -6102,7 +6141,7 @@ pub fn lite_parse(tokens: &[Token]) -> (LiteBlock, Option<ParseError>) {
                         }
                         _ => {
                             curr_pipeline
-                                .push(LiteElement::Command(last_connector_span, curr_command));
+                                .push(LiteElement::Command(Some(token.span), curr_command));
                         }
                     }
 
@@ -6174,7 +6213,10 @@ pub fn lite_parse(tokens: &[Token]) -> (LiteBlock, Option<ParseError>) {
         block.push(curr_pipeline);
     }
 
-    if last_token == TokenContents::Pipe {
+    if last_token == TokenContents::Pipe
+        || last_token == TokenContents::PipePipe
+        || last_token == TokenContents::AndAnd
+    {
         (
             block,
             Some(ParseError::UnexpectedEof(
@@ -6183,7 +6225,7 @@ pub fn lite_parse(tokens: &[Token]) -> (LiteBlock, Option<ParseError>) {
             )),
         )
     } else {
-        (block, error)
+        (block, None)
     }
 }
 

crates/nu-protocol/src/ast/pipeline.rs

@@ -14,7 +14,6 @@ pub enum Redirection {
 pub enum PipelineElement {
     Expression(Option<Span>, Expression),
     Redirection(Span, Redirection, Expression),
-    And(Span, Expression),
     Or(Span, Expression),
 }
 
@@ -23,9 +22,8 @@ impl PipelineElement {
         match self {
             PipelineElement::Expression(None, expression) => expression.span,
             PipelineElement::Expression(Some(span), expression)
-            | PipelineElement::Redirection(span, _, expression)
+            | PipelineElement::Or(span, expression)
-            | PipelineElement::And(span, expression)
+            | PipelineElement::Redirection(span, _, expression) => Span {
-            | PipelineElement::Or(span, expression) => Span {
                 start: span.start,
                 end: expression.span.end,
             },
@@ -35,7 +33,6 @@ impl PipelineElement {
         match self {
             PipelineElement::Expression(_, expression)
             | PipelineElement::Redirection(_, _, expression)
-            | PipelineElement::And(_, expression)
             | PipelineElement::Or(_, expression) => expression.has_in_variable(working_set),
         }
     }
@@ -43,9 +40,8 @@ impl PipelineElement {
     pub fn replace_in_variable(&mut self, working_set: &mut StateWorkingSet, new_var_id: VarId) {
         match self {
             PipelineElement::Expression(_, expression)
-            | PipelineElement::Redirection(_, _, expression)
+            | PipelineElement::Or(_, expression)
-            | PipelineElement::And(_, expression)
+            | PipelineElement::Redirection(_, _, expression) => {
-            | PipelineElement::Or(_, expression) => {
                 expression.replace_in_variable(working_set, new_var_id)
             }
         }
@@ -59,9 +55,8 @@ impl PipelineElement {
     ) {
         match self {
             PipelineElement::Expression(_, expression)
-            | PipelineElement::Redirection(_, _, expression)
+            | PipelineElement::Or(_, expression)
-            | PipelineElement::And(_, expression)
+            | PipelineElement::Redirection(_, _, expression) => {
-            | PipelineElement::Or(_, expression) => {
                 expression.replace_span(working_set, replaced, new_span)
             }
         }

crates/nu-protocol/src/engine/stack.rs

@@ -113,6 +113,13 @@ impl Stack {
             .ok_or_else(|| ShellError::NushellFailed("No active overlay".into()))
     }
 
+    pub fn last_exit_code(&self, engine_state: &EngineState) -> Option<i64> {
+        match self.get_env_var(engine_state, "LAST_EXIT_CODE") {
+            Some(Value::Int { val, .. }) => Some(val),
+            _ => None,
+        }
+    }
+
     pub fn captures_to_stack(&self, captures: &HashMap<VarId, Value>) -> Stack {
         // FIXME: this is probably slow
         let mut env_vars = self.env_vars.clone();

tests/shell/pipeline/mod.rs

@@ -1,4 +1,5 @@
 mod commands;
+mod pipeline_operators;
 
 use nu_test_support::nu;
 

tests/shell/pipeline/pipeline_operators.rs

@@ -0,0 +1,74 @@
+use nu_test_support::nu;
+
+#[test]
+fn and_operator1() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            3 / 0 && 2 + 3
+        "#
+    );
+
+    assert!(actual.err.contains("division by zero"));
+}
+
+#[test]
+fn and_operator2() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            0 | 3 / $in && 2 + 3
+        "#
+    );
+
+    assert!(actual.err.contains("division by zero"));
+}
+
+#[test]
+fn or_operator1() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            3 / 0 || 2 + 3
+        "#
+    );
+
+    assert!(actual.out.contains('5'));
+}
+
+#[test]
+fn or_operator2() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            0 | 3 / $in || 2 + 3
+        "#
+    );
+
+    assert!(actual.out.contains('5'));
+}
+
+#[test]
+fn or_operator3() {
+    // On success, don't run the next step
+    let actual = nu!(
+        cwd: ".",
+        r#"
+            0 || 2 + 3
+        "#
+    );
+
+    assert_eq!(actual.out, "0");
+}
+
+#[test]
+fn or_operator4() {
+    let actual = nu!(
+        cwd: ".",
+        r#"
+        1 / 0 || 2 / 0 || 10 + 9
+        "#
+    );
+
+    assert!(actual.out.contains("19"));
+}