Add support for while loops (#7101)

crates/nu-command/src/core_commands/mod.rs

@@ -28,6 +28,7 @@ mod mut_;
 pub(crate) mod overlay;
 mod use_;
 mod version;
+mod while_;
 
 pub use alias::Alias;
 pub use ast::Ast;
@@ -59,6 +60,7 @@ pub use mut_::Mut;
 pub use overlay::*;
 pub use use_::Use;
 pub use version::Version;
+pub use while_::While;
 #[cfg(feature = "plugin")]
 mod register;
 

crates/nu-command/src/core_commands/while_.rs

@@ -0,0 +1,99 @@
+use nu_engine::{eval_block, eval_expression, CallExt};
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Block, Command, EngineState, Stack};
+use nu_protocol::{Category, Example, PipelineData, ShellError, Signature, SyntaxShape, Value};
+
+#[derive(Clone)]
+pub struct While;
+
+impl Command for While {
+    fn name(&self) -> &str {
+        "while"
+    }
+
+    fn usage(&self) -> &str {
+        "Conditionally run a block in a loop."
+    }
+
+    fn signature(&self) -> nu_protocol::Signature {
+        Signature::build("while")
+            .required("cond", SyntaxShape::Expression, "condition to check")
+            .required(
+                "block",
+                SyntaxShape::Block,
+                "block to loop if check succeeds",
+            )
+            .category(Category::Core)
+    }
+
+    fn extra_usage(&self) -> &str {
+        r#"This command is a parser keyword. For details, check:
+  https://www.nushell.sh/book/thinking_in_nu.html"#
+    }
+
+    fn is_parser_keyword(&self) -> bool {
+        true
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<nu_protocol::PipelineData, nu_protocol::ShellError> {
+        let cond = call.positional_nth(0).expect("checked through parser");
+        let block: Block = call.req(engine_state, stack, 1)?;
+
+        loop {
+            let result = eval_expression(engine_state, stack, cond)?;
+            match &result {
+                Value::Bool { val, .. } => {
+                    if *val {
+                        let block = engine_state.get_block(block.block_id);
+                        eval_block(
+                            engine_state,
+                            stack,
+                            block,
+                            PipelineData::new(call.head),
+                            call.redirect_stdout,
+                            call.redirect_stderr,
+                        )?
+                        .into_value(call.head);
+                    } else {
+                        break;
+                    }
+                }
+                x => {
+                    return Err(ShellError::CantConvert(
+                        "bool".into(),
+                        x.get_type().to_string(),
+                        result.span()?,
+                        None,
+                    ))
+                }
+            }
+        }
+        Ok(PipelineData::new(call.head))
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![Example {
+            description: "Loop while a condition is true",
+            example: "mut x = 0; while $x < 10 { $x = $x + 1 }",
+            result: None,
+        }]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_examples() {
+        use crate::test_examples;
+
+        test_examples(While {})
+    }
+}

crates/nu-command/src/default_context.rs

@@ -62,6 +62,7 @@ pub fn create_default_context() -> EngineState {
             Mut,
             Use,
             Version,
+            While,
         };
 
         // Charts

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

@@ -88,6 +88,7 @@ mod use_;
 mod where_;
 #[cfg(feature = "which-support")]
 mod which;
+mod while_;
 mod with_env;
 mod wrap;
 mod zip;

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

@@ -0,0 +1,11 @@
+use nu_test_support::nu;
+
+#[test]
+fn while_sum() {
+    let actual = nu!(
+        cwd: ".",
+        "mut total = 0; mut x = 0; while $x <= 10 { $total = $total + $x; $x = $x + 1 }; $total"
+    );
+
+    assert_eq!(actual.out, "55");
+}

crates/nu-parser/tests/test_parser.rs

@@ -968,7 +968,6 @@ mod input_types {
             working_set.add_decl(Box::new(GroupBy));
             working_set.add_decl(Box::new(LsTest));
             working_set.add_decl(Box::new(ToCustom));
-            working_set.add_decl(Box::new(Let));
             working_set.add_decl(Box::new(AggMin));
             working_set.add_decl(Box::new(Collect));
             working_set.add_decl(Box::new(WithColumn));