Add or-patterns, fix var binding scope (#8633)

# Description

Adds `|` patterns to `match`, allowing you to try multiple patterns for
the same case.

Example:

```
match {b: 1} { {a: $b} | {b: $b} => { print $b } }
```

Variables that don't bind are set to `$nothing` so that they can be
later checked.

This PR also:
fixes #8631 

Creates a set of integration tests for pattern matching also

# User-Facing Changes

Adds `|` to `match`. Fixes variable binding scope. 
# 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

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```

# 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-command/tests/commands/match_.rs

@@ -0,0 +1,177 @@
+use nu_test_support::nu;
+
+#[test]
+fn match_for_range() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match 3 { 1..10 => { print "success" } }"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_for_range_unmatched() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match 11 { 1..10 => { print "failure" }, _ => { print "success" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_for_record() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match {a: 11} { {a: $b} => { print $b }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "11");
+}
+
+#[test]
+fn match_for_record_shorthand() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match {a: 12} { {$a} => { print $a }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "12");
+}
+
+#[test]
+fn match_list() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match [1, 2] { [$a] => { print $"single: ($a)" }, [$b, $c] => {print $"double: ($b) ($c)"}}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "double: 1 2");
+}
+
+#[test]
+fn match_constant_1() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match 2 { 1 => { print "failure"}, 2 => { print "success" }, 3 => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_constant_2() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match 2.3 { 1.4 => { print "failure"}, 2.3 => { print "success" }, 3 => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_constant_3() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match true { false => { print "failure"}, true => { print "success" }, 3 => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_constant_4() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match "def" { "abc" => { print "failure"}, "def" => { print "success" }, "ghi" => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_constant_5() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match 2019-08-23 { 2010-01-01 => { print "failure"}, 2019-08-23 => { print "success" }, 2020-02-02 => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_constant_6() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match 6sec { 2sec => { print "failure"}, 6sec => { print "success" }, 1min => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_constant_7() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match 1kib { 1kb => { print "failure"}, 1kib => { print "success" }, 2kb => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success");
+}
+
+#[test]
+fn match_or_pattern() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match {b: 7} { {a: $a} | {b: $b} => { print $"success: ($b)" }, _ => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success: 7");
+}
+
+#[test]
+fn match_or_pattern_overlap_1() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match {a: 7} { {a: $b} | {b: $b} => { print $"success: ($b)" }, _ => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success: 7");
+}
+
+#[test]
+fn match_or_pattern_overlap_2() {
+    let actual = nu!(
+        cwd: ".",
+        r#"match {b: 7} { {a: $b} | {b: $b} => { print $"success: ($b)" }, _ => { print "failure" }}"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "success: 7");
+}
+
+#[test]
+fn match_doesnt_overwrite_variable() {
+    let actual = nu!(
+        cwd: ".",
+        r#"let b = 100; match 55 { $b => {} }; print $b"#
+    );
+    // Make sure we don't see any of these values in the output
+    // As we do not auto-print loops anymore
+    assert_eq!(actual.out, "100");
+}

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

@@ -48,6 +48,7 @@ mod let_;
 mod lines;
 mod loop_;
 mod ls;
+mod match_;
 mod math;
 mod merge;
 mod mkdir;

crates/nu-parser/src/flatten.rs

@@ -559,6 +559,11 @@ pub fn flatten_pattern(match_pattern: &MatchPattern) -> Vec<(Span, FlatShape)> {
         Pattern::Variable(_) => {
             output.push((match_pattern.span, FlatShape::Variable));
         }
+        Pattern::Or(patterns) => {
+            for pattern in patterns {
+                output.extend(flatten_pattern(pattern));
+            }
+        }
     }
     output
 }

crates/nu-parser/src/parse_patterns.rs

@@ -79,7 +79,7 @@ pub fn parse_variable_pattern(
     let bytes = working_set.get_span_contents(span);
 
     if is_variable(bytes) {
-        if let Some(var_id) = working_set.find_variable(bytes) {
+        if let Some(var_id) = working_set.find_variable_in_current_frame(bytes) {
             (
                 MatchPattern {
                     pattern: Pattern::Variable(var_id),

crates/nu-parser/src/parser.rs

@@ -4526,7 +4526,7 @@ pub fn parse_match_block_expression(
 
     let source = working_set.get_span_contents(inner_span);
 
-    let (output, err) = lex(source, start, &[b' ', b'\r', b'\n', b','], &[], false);
+    let (output, err) = lex(source, start, &[b' ', b'\r', b'\n', b',', b'|'], &[], false);
     error = error.or(err);
 
     let mut position = 0;
@@ -4539,7 +4539,7 @@ pub fn parse_match_block_expression(
         working_set.enter_scope();
 
         // First parse the pattern
-        let (pattern, err) = parse_pattern(working_set, output[position].span);
+        let (mut pattern, err) = parse_pattern(working_set, output[position].span);
         error = error.or(err);
 
         position += 1;
@@ -4555,19 +4555,75 @@ pub fn parse_match_block_expression(
             break;
         }
 
-        // Then the =>
+        // Multiple patterns connected by '|'
-        let thick_arrow = working_set.get_span_contents(output[position].span);
+        let mut connector = working_set.get_span_contents(output[position].span);
-        if thick_arrow != b"=>" {
+        if connector == b"|" && position < output.len() {
+            let mut or_pattern = vec![pattern];
+
+            while connector == b"|" && position < output.len() {
+                connector = b"";
+
+                position += 1;
+
+                if position >= output.len() {
+                    error = error.or(Some(ParseError::Mismatch(
+                        "pattern".into(),
+                        "end of input".into(),
+                        Span::new(output[position - 1].span.end, output[position - 1].span.end),
+                    )));
+
+                    working_set.exit_scope();
+                    break;
+                }
+
+                let (pattern, err) = parse_pattern(working_set, output[position].span);
+                error = error.or(err);
+                or_pattern.push(pattern);
+
+                position += 1;
+                if position >= output.len() {
+                    error = error.or(Some(ParseError::Mismatch(
+                        "=>".into(),
+                        "end of input".into(),
+                        Span::new(output[position - 1].span.end, output[position - 1].span.end),
+                    )));
+
+                    working_set.exit_scope();
+                    break;
+                } else {
+                    connector = working_set.get_span_contents(output[position].span);
+                }
+            }
+
+            let start = or_pattern
+                .first()
+                .expect("internal error: unexpected state of or-pattern")
+                .span
+                .start;
+            let end = or_pattern
+                .last()
+                .expect("internal error: unexpected state of or-pattern")
+                .span
+                .end;
+
+            pattern = MatchPattern {
+                pattern: Pattern::Or(or_pattern),
+                span: Span::new(start, end),
+            }
+        }
+
+        // Then the `=>` arrow
+        if connector != b"=>" {
             error = error.or(Some(ParseError::Mismatch(
                 "=>".into(),
                 "end of input".into(),
                 Span::new(output[position - 1].span.end, output[position - 1].span.end),
             )));
+        } else {
+            position += 1;
         }
 
         // Finally, the value/expression/block that we will run to produce the result
-        position += 1;
-
         if position >= output.len() {
             error = error.or(Some(ParseError::Mismatch(
                 "match result".into(),
@@ -6094,6 +6150,11 @@ pub fn discover_captures_in_pattern(pattern: &MatchPattern, seen: &mut Vec<VarId
                 discover_captures_in_pattern(&item.1, seen)
             }
         }
+        Pattern::Or(patterns) => {
+            for pattern in patterns {
+                discover_captures_in_pattern(pattern, seen)
+            }
+        }
         Pattern::Value(_) | Pattern::IgnoreValue | Pattern::Garbage => {}
     }
 }

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

@@ -10,12 +10,48 @@ pub struct MatchPattern {
     pub span: Span,
 }
 
+impl MatchPattern {
+    pub fn variables(&self) -> Vec<VarId> {
+        self.pattern.variables()
+    }
+}
+
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
 pub enum Pattern {
     Record(Vec<(String, MatchPattern)>),
     List(Vec<MatchPattern>),
     Value(Expression),
     Variable(VarId),
+    Or(Vec<MatchPattern>),
     IgnoreValue, // the _ pattern
     Garbage,
 }
+
+impl Pattern {
+    pub fn variables(&self) -> Vec<VarId> {
+        let mut output = vec![];
+        match self {
+            Pattern::Record(items) => {
+                for item in items {
+                    output.append(&mut item.1.variables());
+                }
+            }
+            Pattern::List(items) => {
+                for item in items {
+                    output.append(&mut item.variables());
+                }
+            }
+            Pattern::Value(_) => {}
+            Pattern::Variable(var_id) => output.push(*var_id),
+            Pattern::Or(patterns) => {
+                for pattern in patterns {
+                    output.append(&mut pattern.variables());
+                }
+            }
+            Pattern::IgnoreValue => {}
+            Pattern::Garbage => {}
+        }
+
+        output
+    }
+}

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

@@ -1803,6 +1803,24 @@ impl<'a> StateWorkingSet<'a> {
         None
     }
 
+    pub fn find_variable_in_current_frame(&self, name: &[u8]) -> Option<VarId> {
+        let mut removed_overlays = vec![];
+
+        for scope_frame in self.delta.scope.iter().rev().take(1) {
+            for overlay_frame in scope_frame
+                .active_overlays(&mut removed_overlays)
+                .iter()
+                .rev()
+            {
+                if let Some(var_id) = overlay_frame.vars.get(name) {
+                    return Some(*var_id);
+                }
+            }
+        }
+
+        None
+    }
+
     pub fn add_variable(
         &mut self,
         mut name: Vec<u8>,

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

@@ -1,6 +1,6 @@
 use crate::{
     ast::{Expr, MatchPattern, Pattern, RangeInclusion},
-    Unit, Value, VarId,
+    Span, Unit, Value, VarId,
 };
 
 pub trait Matcher {
@@ -217,6 +217,54 @@ impl Matcher for Pattern {
                     _ => false,
                 }
             }
+            Pattern::Or(patterns) => {
+                let mut result = false;
+
+                for pattern in patterns {
+                    let mut local_matches = vec![];
+                    if !result {
+                        if pattern.match_value(value, &mut local_matches) {
+                            // TODO: do we need to replace previous variables that defaulted to nothing?
+                            matches.append(&mut local_matches);
+                            result = true;
+                        } else {
+                            // Create variables that don't match and assign them to null
+                            let vars = pattern.variables();
+                            for var in &vars {
+                                let mut found = false;
+                                for match_ in matches.iter() {
+                                    if match_.0 == *var {
+                                        found = true;
+                                    }
+                                }
+
+                                if !found {
+                                    // FIXME: don't use Span::unknown()
+                                    matches.push((*var, Value::nothing(Span::unknown())))
+                                }
+                            }
+                        }
+                    } else {
+                        // We already have a match, so ignore the remaining match variables
+                        // And assign them to null
+                        let vars = pattern.variables();
+                        for var in &vars {
+                            let mut found = false;
+                            for match_ in matches.iter() {
+                                if match_.0 == *var {
+                                    found = true;
+                                }
+                            }
+
+                            if !found {
+                                // FIXME: don't use Span::unknown()
+                                matches.push((*var, Value::nothing(Span::unknown())))
+                            }
+                        }
+                    }
+                }
+                result
+            }
         }
     }
 }