Change how and and or operations are compiled to IR to support custom values (#14653)

# Description

Because `and` and `or` are short-circuiting operations in Nushell, they
must be compiled to a sequence that avoids evaluating the RHS if the LHS
is already sufficient to determine the output - i.e., `false` for `and`
and `true` for `or`. I initially implemented this with `branch-if`
instructions, simply returning the RHS if it needed to be evaluated, and
returning the short-circuited boolean value if it did not.

Example for `$a and $b`:

```
   0: load-variable          %0, var 999 "$a"
   1: branch-if              %0, 3
   2: jump                   5
   3: load-variable          %0, var 1000 "$b" # label(0), from(1:)
   4: jump                   6
   5: load-literal           %0, bool(false) # label(1), from(2:)
   6: span                   %0          # label(2), from(4:)
   7: return                 %0
```

Unfortunately, this broke polars, because using `and`/`or` on custom
values is perfectly valid and they're allowed to define that behavior
differently, and the polars plugin uses this for boolean masks. But
without using the `binary-op` instruction, that custom behavior is never
invoked. Additionally, `branch-if` requires a boolean, and custom values
are not booleans. This changes the IR to the following, using the
`match` instruction to check for the specific short-circuit value
instead, and still invoking `binary-op` otherwise:

```
   0: load-variable          %0, var 125 "$a"
   1: match                  (false), %0, 4
   2: load-variable          %1, var 124 "$b"
   3: binary-op              %0, Boolean(And), %1
   4: span                   %0          # label(0), from(1:)
   5: return                 %0
```

I've also renamed `Pattern::Value` to `Pattern::Expression` and added a
proper `Pattern::Value` variant that actually contains a `Value`
instead. I'm still hoping to remove `Pattern::Expression` eventually,
because it's kind of a hack - we don't actually evaluate the expression,
we just match it against a few cases specifically for pattern matching,
and it's one of the cases where AST leaks into IR and I want to remove
all of those cases, because AST should not leak into IR.

Fixes #14518

# User-Facing Changes

- `and` and `or` now support custom values again.
- the IR is actually a little bit cleaner, though it may be a bit
slower; `match` is more complex.

# Tests + Formatting

The existing tests pass, but I didn't add anything new. Unfortunately I
don't think there's anything built-in to trigger this, but maybe some
testcases could be added to polars to test it.

crates/nu-engine/src/compile/builder.rs

@@ -1,4 +1,5 @@
 use nu_protocol::{
+    ast::Pattern,
     ir::{DataSlice, Instruction, IrAstRef, IrBlock, Literal},
     CompileError, IntoSpanned, RegId, Span, Spanned,
 };
@@ -426,6 +427,24 @@ impl BlockBuilder {
         self.push(Instruction::Jump { index: label_id.0 }.into_spanned(span))
     }
 
+    /// Add a `match` instruction
+    pub(crate) fn r#match(
+        &mut self,
+        pattern: Pattern,
+        src: RegId,
+        label_id: LabelId,
+        span: Span,
+    ) -> Result<(), CompileError> {
+        self.push(
+            Instruction::Match {
+                pattern: Box::new(pattern),
+                src,
+                index: label_id.0,
+            }
+            .into_spanned(span),
+        )
+    }
+
     /// The index that the next instruction [`.push()`](Self::push)ed will have.
     pub(crate) fn here(&self) -> usize {
         self.instructions.len()

crates/nu-engine/src/compile/keyword.rs

@@ -197,13 +197,11 @@ pub(crate) fn compile_match(
     for (pattern, _) in match_block {
         let match_label = builder.label(None);
         match_labels.push(match_label);
-        builder.push(
-            Instruction::Match {
-                pattern: Box::new(pattern.pattern.clone()),
-                src: match_reg,
-                index: match_label.0,
-            }
-            .into_spanned(pattern.span),
+        builder.r#match(
+            pattern.pattern.clone(),
+            match_reg,
+            match_label,
+            pattern.span,
         )?;
         // Also add a label for the next match instruction or failure case
         next_labels.push(builder.label(Some(builder.here())));

crates/nu-engine/src/compile/operator.rs

@@ -1,8 +1,8 @@
 use nu_protocol::{
-    ast::{Assignment, Boolean, CellPath, Expr, Expression, Math, Operator, PathMember},
+    ast::{Assignment, Boolean, CellPath, Expr, Expression, Math, Operator, PathMember, Pattern},
     engine::StateWorkingSet,
     ir::{Instruction, Literal},
-    IntoSpanned, RegId, Span, Spanned, ENV_VARIABLE_ID,
+    IntoSpanned, RegId, Span, Spanned, Value, ENV_VARIABLE_ID,
 };
 use nu_utils::IgnoreCaseExt;
 
@@ -59,56 +59,52 @@ pub(crate) fn compile_binary_op(
         )?;
 
         match op.item {
-            // `and` / `or` are short-circuiting, and we can get by with one register and a branch
-            Operator::Boolean(Boolean::And) => {
-                let true_label = builder.label(None);
-                builder.branch_if(lhs_reg, true_label, op.span)?;
+            // `and` / `or` are short-circuiting, use `match` to avoid running the RHS if LHS is
+            // the correct value. Be careful to support and/or on non-boolean values
+            Operator::Boolean(bool_op @ Boolean::And)
+            | Operator::Boolean(bool_op @ Boolean::Or) => {
+                // `and` short-circuits on false, and `or` short-circuits on true.
+                let short_circuit_value = match bool_op {
+                    Boolean::And => false,
+                    Boolean::Or => true,
+                    Boolean::Xor => unreachable!(),
+                };
 
-                // If the branch was not taken it's false, so short circuit to load false
-                let false_label = builder.label(None);
-                builder.jump(false_label, op.span)?;
+                // Short-circuit to return `lhs_reg`. `match` op does not consume `lhs_reg`.
+                let short_circuit_label = builder.label(None);
+                builder.r#match(
+                    Pattern::Value(Value::bool(short_circuit_value, op.span)),
+                    lhs_reg,
+                    short_circuit_label,
+                    op.span,
+                )?;
 
-                builder.set_label(true_label, builder.here())?;
+                // If the match failed then this was not the short-circuit value, so we have to run
+                // the RHS expression
+                let rhs_reg = builder.next_register()?;
                 compile_expression(
                     working_set,
                     builder,
                     rhs,
                     RedirectModes::value(rhs.span),
                     None,
-                    lhs_reg,
+                    rhs_reg,
                 )?;
 
-                let end_label = builder.label(None);
-                builder.jump(end_label, op.span)?;
-
-                // Consumed by `branch-if`, so we have to set it false again
-                builder.set_label(false_label, builder.here())?;
-                builder.load_literal(lhs_reg, Literal::Bool(false).into_spanned(lhs.span))?;
-
-                builder.set_label(end_label, builder.here())?;
+                // It may seem intuitive that we can just return RHS here, but we do have to
+                // actually execute the binary-op in case this is not a boolean
+                builder.push(
+                    Instruction::BinaryOp {
+                        lhs_dst: lhs_reg,
+                        op: Operator::Boolean(bool_op),
+                        rhs: rhs_reg,
                     }
-            Operator::Boolean(Boolean::Or) => {
-                let true_label = builder.label(None);
-                builder.branch_if(lhs_reg, true_label, op.span)?;
-
-                // If the branch was not taken it's false, so do the right-side expression
-                compile_expression(
-                    working_set,
-                    builder,
-                    rhs,
-                    RedirectModes::value(rhs.span),
-                    None,
-                    lhs_reg,
+                    .into_spanned(op.span),
                 )?;
 
-                let end_label = builder.label(None);
-                builder.jump(end_label, op.span)?;
-
-                // Consumed by `branch-if`, so we have to set it true again
-                builder.set_label(true_label, builder.here())?;
-                builder.load_literal(lhs_reg, Literal::Bool(true).into_spanned(lhs.span))?;
-
-                builder.set_label(end_label, builder.here())?;
+                // In either the short-circuit case or other case, the result is in lhs_reg =
+                // out_reg
+                builder.set_label(short_circuit_label, builder.here())?;
             }
             _ => {
                 // Any other operator, via `binary-op`

crates/nu-parser/src/flatten.rs

@@ -644,7 +644,9 @@ fn flatten_pattern_into(match_pattern: &MatchPattern, output: &mut Vec<(Span, Fl
                 output.push((match_pattern.span, FlatShape::MatchPattern));
             }
         }
-        Pattern::Value(_) => output.push((match_pattern.span, FlatShape::MatchPattern)),
+        Pattern::Expression(_) | Pattern::Value(_) => {
+            output.push((match_pattern.span, FlatShape::MatchPattern))
+        }
         Pattern::Variable(var_id) => output.push((match_pattern.span, FlatShape::VarDecl(*var_id))),
         Pattern::Rest(var_id) => output.push((match_pattern.span, FlatShape::VarDecl(*var_id))),
         Pattern::Or(patterns) => {

crates/nu-parser/src/parse_patterns.rs

@@ -40,7 +40,7 @@ pub fn parse_pattern(working_set: &mut StateWorkingSet, span: Span) -> MatchPatt
         let value = parse_value(working_set, span, &SyntaxShape::Any);
 
         MatchPattern {
-            pattern: Pattern::Value(Box::new(value)),
+            pattern: Pattern::Expression(Box::new(value)),
             guard: None,
             span,
         }

crates/nu-parser/src/parser.rs

@@ -6286,7 +6286,11 @@ pub fn discover_captures_in_pattern(pattern: &MatchPattern, seen: &mut Vec<VarId
             }
         }
         Pattern::Rest(var_id) => seen.push(*var_id),
-        Pattern::Value(_) | Pattern::IgnoreValue | Pattern::IgnoreRest | Pattern::Garbage => {}
+        Pattern::Expression(_)
+        | Pattern::Value(_)
+        | Pattern::IgnoreValue
+        | Pattern::IgnoreRest
+        | Pattern::Garbage => {}
     }
 }
 

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

@@ -1,5 +1,5 @@
 use super::Expression;
-use crate::{Span, VarId};
+use crate::{Span, Value, VarId};
 use serde::{Deserialize, Serialize};
 
 /// AST Node for match arm with optional match guard
@@ -23,10 +23,12 @@ pub enum Pattern {
     Record(Vec<(String, MatchPattern)>),
     /// List destructuring
     List(Vec<MatchPattern>),
-    /// Matching against a literal
+    /// Matching against a literal (from expression result)
     // TODO: it would be nice if this didn't depend on AST
     // maybe const evaluation can get us to a Value instead?
-    Value(Box<Expression>),
+    Expression(Box<Expression>),
+    /// Matching against a literal (pure value)
+    Value(Value),
     /// binding to a variable
     Variable(VarId),
     /// the `pattern1 \ pattern2` or-pattern
@@ -62,7 +64,11 @@ impl Pattern {
                 }
             }
             Pattern::Rest(var_id) => output.push(*var_id),
-            Pattern::Value(_) | Pattern::IgnoreValue | Pattern::Garbage | Pattern::IgnoreRest => {}
+            Pattern::Expression(_)
+            | Pattern::Value(_)
+            | Pattern::IgnoreValue
+            | Pattern::Garbage
+            | Pattern::IgnoreRest => {}
         }
 
         output

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

@@ -94,7 +94,7 @@ impl Matcher for Pattern {
                 }
                 _ => false,
             },
-            Pattern::Value(pattern_value) => {
+            Pattern::Expression(pattern_value) => {
                 // TODO: Fill this out with the rest of them
                 match &pattern_value.expr {
                     Expr::Nothing => {
@@ -205,6 +205,7 @@ impl Matcher for Pattern {
                     _ => false,
                 }
             }
+            Pattern::Value(pattern_value) => value == pattern_value,
             Pattern::Or(patterns) => {
                 let mut result = false;
 

crates/nu-protocol/src/ir/display.rs

@@ -419,11 +419,14 @@ impl<'a> fmt::Display for FmtPattern<'a> {
                 }
                 f.write_str("]")
             }
-            Pattern::Value(expr) => {
+            Pattern::Expression(expr) => {
                 let string =
                     String::from_utf8_lossy(self.engine_state.get_span_contents(expr.span));
                 f.write_str(&string)
             }
+            Pattern::Value(value) => {
+                f.write_str(&value.to_parsable_string(", ", &self.engine_state.config))
+            }
             Pattern::Variable(var_id) => {
                 let variable = FmtVar::new(self.engine_state, *var_id);
                 write!(f, "{}", variable)