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# 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. |
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nu-protocol
The nu-protocol crate holds the definitions of structs/traits that are used throughout Nushell. This gives us one way to expose them to many other crates, as well as make these definitions available to each other, without causing mutually recursive dependencies.