`if let` and `while let` support by sbillig · Pull Request #1282 · argotorg/fe

sbillig · 2026-02-25T04:01:46Z

We don't support rust-2024-style if-let in compound conditions yet (eg if let .. = y && let ... && foo {

This also fixes a loop-lowering bug in yul codegen.

sbillig · 2026-02-25T04:06:00Z

Maybe we could remove tree sitter parser.c from the repo and generate it on the fly? Then we won't have 35k line diffs every time we make a syntax change.

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crates/hir/src/core/lower/expr.rs

sbillig · 2026-02-27T19:47:26Z

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chatgpt-codex-connector · 2026-02-27T19:57:43Z

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Pull request overview

Adds support for Rust-2024-style if let / while let condition expressions (including && let-chains) across parsing → HIR lowering/typecheck/CTFE → MIR lowering → codegen, and fixes a Yul loop-lowering/control-flow emission bug.

Changes:

Extend the parser and tree-sitter grammar to recognize condition-only let expressions in if/while, including && chains and a grammar-level restriction against mixing unparenthesized || with let conditions.
Introduce a dedicated HIR Cond tree (separate from Expr) and update visitors, type checking, const checks, and CTFE to evaluate/validate condition chains and their bindings correctly.
Update MIR lowering and Yul emission to handle condition decision trees (not just a single branch terminator) and fix loop/control-flow lowering issues; refresh snapshots and formatting fixtures accordingly.

Reviewed changes

Copilot reviewed 74 out of 75 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/uitest/fixtures/ty_check/if_let_chain_scope.snap	New snapshot asserting `let`-chain bindings don’t leak outside condition/body scopes.
crates/uitest/fixtures/ty_check/if_let_chain_scope.fe	New typecheck fixture for `if let` / `while let` chains and scoping.
crates/uitest/fixtures/ty_check/const_eval/if_let_condition.snap	New snapshot for const-eval + `if let` condition behavior.
crates/uitest/fixtures/ty_check/const_eval/if_let_condition.fe	New CTFE fixture using `if let` in a `const fn` context.
crates/uitest/fixtures/parser/if_let_or_chain.snap	New parser diagnostic snapshot for `
crates/uitest/fixtures/parser/if_let_or_chain.fe	New parser fixture exercising `if let ...
crates/tree-sitter-fe/src/node-types.json	Adds node types for condition-specific binary expressions and `let_condition`.
crates/tree-sitter-fe/src/grammar.json	Adds condition sub-grammars to model `let` conditions and restrict `
crates/tree-sitter-fe/grammar.js	Implements condition-only `let_condition` + condition grammar variants and conflicts.
crates/parser/test_files/syntax_node/stmts/while.snap	Updates syntax-node snapshot to include `while let` parsing.
crates/parser/test_files/syntax_node/stmts/while.fe	Adds `while let` examples to parser test input.
crates/parser/test_files/syntax_node/exprs/if.snap	Updates syntax-node snapshot to include `if let` parsing.
crates/parser/test_files/syntax_node/exprs/if.fe	Adds `if let` examples (incl. `else if let`) to parser test input.
crates/parser/src/syntax_kind.rs	Introduces `SyntaxKind::LetExpr` for condition-only `let` expressions.
crates/parser/src/parser/stmt.rs	Switches `while` condition parsing to `parse_condition_expr`.
crates/parser/src/parser/expr_atom.rs	Switches `if` condition parsing to `parse_condition_expr`.
crates/parser/src/parser/expr.rs	Implements condition parsing with `let` expressions and `
crates/parser/src/ast/stmt.rs	Adds AST tests for `while let` condition parsing and `
crates/parser/src/ast/expr.rs	Adds AST support/tests for `LetExpr` and let-chains in `if` conditions.
crates/mir/tests/fixtures/trait_assoc_fn_call.mir.snap	Snapshot update due to control-flow lowering changes.
crates/mir/tests/fixtures/if_let_while_let.mir.snap	New MIR snapshot validating `if let` / `while let` lowering.
crates/mir/tests/fixtures/if_let_while_let.fe	New MIR fixture covering `if let` and `while let`.
crates/mir/tests/fixtures/for_continue.mir.snap	Snapshot update due to branch lowering changes.
crates/mir/tests/fixtures/echo.mir.snap	Snapshot update due to branch lowering changes.
crates/mir/tests/fixtures/contract_field_layout_slots_const_hole.mir.snap	Snapshot update due to branch lowering changes.
crates/mir/tests/fixtures/const_hole_storage_map_contract_defaults.mir.snap	Snapshot update due to branch lowering changes.
crates/mir/tests/fixtures/abi_decode.mir.snap	Snapshot update due to branch lowering changes.
crates/mir/src/lower/mod.rs	Updates MIR builder to traverse the new `Cond` structure for return-param collection.
crates/mir/src/lower/match_lowering.rs	Adds lowering for `let` conditions into match/decision-tree branching.
crates/mir/src/lower/expr.rs	Lowers `if`/`while` using `CondId` via `lower_condition_branch` (supports decision trees).
crates/language-server/test_files/completion.snap	Snapshot update (completion list shifted by unrelated symbol set changes).
crates/hir/tests/ty_check.rs	Skips unresolved spans when collecting typed-property snapshots (stability fix).
crates/hir/test_files/ty_check/if_.snap	Snapshot update reflecting `if let` typing and new test cases.
crates/hir/test_files/ty_check/if_.fe	Adds `if let` typing test (no-else behavior) and updates file layout.
crates/hir/test_files/ty_check/contract_effects.snap	Snapshot update due to condition typing/printing changes.
crates/hir/src/core/visitor.rs	Updates visitor traversal to walk `Cond` trees (and bind patterns/exprs inside).
crates/hir/src/core/print.rs	Adds pretty-printing for `Cond` nodes.
crates/hir/src/core/lower/stmt.rs	Lowers `while` condition into `Cond` instead of `Expr`.
crates/hir/src/core/lower/expr.rs	Lowers `if` condition into `Cond` and rejects direct lowering of `let` as normal `Expr`.
crates/hir/src/core/lower/event.rs	Threads `conds` store into body creation for event lowering.
crates/hir/src/core/lower/body.rs	Adds `conds` NodeStore to `Body` lowering context and final body assembly.
crates/hir/src/core/hir_def/stmt.rs	Changes `While` to store `CondId` instead of `ExprId`.
crates/hir/src/core/hir_def/expr.rs	Introduces `Cond` / `CondId` and changes `Expr::If` to store `CondId`.
crates/hir/src/core/hir_def/body.rs	Adds `conds` NodeStore to `Body`.
crates/hir/src/analysis/ty/ty_check/stmt.rs	Typechecks `while` via `check_cond` with correct scoping/pending-binding handling.
crates/hir/src/analysis/ty/ty_check/expr.rs	Implements `check_cond` + `check_let_condition`; updates `if` typing/scoping for let-chains.
crates/hir/src/analysis/ty/ty_check/env.rs	Adds `enter_lexical_scope` and `clear_pending_bindings` utilities for let-chain handling.
crates/hir/src/analysis/ty/ctfe.rs	Adds `eval_cond` so CTFE can evaluate let-conditions and logical condition chains.
crates/hir/src/analysis/ty/const_check.rs	Adds `check_cond` so const checking visits let-conditions and condition trees.
crates/fmt/tests/fixtures/loops.snap	Snapshot update for formatted `while let`.
crates/fmt/tests/fixtures/loops.fe	Adds unformatted `while let` case to formatter fixtures.
crates/fmt/tests/fixtures/if_else_width.snap	Snapshot update to include `if let` width behavior.
crates/fmt/tests/fixtures/if_else_width.fe	Adds unformatted `if let` single-line case to formatter fixtures.
crates/fmt/src/ast/types.rs	Adds formatting dispatch for `ExprKind::Let`.
crates/fmt/src/ast/stmt.rs	Adjusts `while` formatting node handling (robustness with new AST shape).
crates/fmt/src/ast/expr.rs	Adds `LetExpr` formatter and adjusts `if` formatting node handling (robustness).
crates/fe/tests/fixtures/fe_test/if_let_while_let.fe	End-to-end test fixture for `if let` / `while let` (incl. let-chains).
crates/codegen/tests/fixtures/sonatina_ir/range_bounds.snap	Snapshot update from changed branching lowering patterns.
crates/codegen/tests/fixtures/sonatina_ir/if_else.snap	Snapshot update from changed branching lowering patterns.
crates/codegen/tests/fixtures/sonatina_ir/high_level_contract.snap	Snapshot update from changed branching lowering patterns.
crates/codegen/tests/fixtures/sonatina_ir/for_range.snap	Snapshot update from changed branching lowering patterns.
crates/codegen/tests/fixtures/sonatina_ir/erc20.snap	Snapshot update from changed branching lowering patterns.
crates/codegen/tests/fixtures/sonatina_ir/create_contract.snap	Snapshot update from changed branching lowering patterns.
crates/codegen/tests/fixtures/sonatina_ir/const_fn_packed_config.snap	Snapshot update from changed branching lowering patterns.
crates/codegen/tests/fixtures/sonatina_ir/const_array_branch.snap	Snapshot update from changed branching lowering patterns.
crates/codegen/tests/fixtures/range_bounds.snap	Snapshot update of Yul output due to branch emission changes.
crates/codegen/tests/fixtures/if_else.snap	Snapshot update of Yul output due to branch emission changes.
crates/codegen/tests/fixtures/high_level_contract.snap	Snapshot update of Yul output due to branch emission changes.
crates/codegen/tests/fixtures/for_range.snap	Snapshot update of Yul output due to branch emission changes.
crates/codegen/tests/fixtures/erc20.snap	Snapshot update of Yul output due to branch emission changes.
crates/codegen/tests/fixtures/create_contract.snap	Snapshot update of Yul output due to branch emission changes.
crates/codegen/tests/fixtures/const_fn_packed_config.snap	Snapshot update of Yul output due to branch emission changes.
crates/codegen/tests/fixtures/const_array_branch.snap	Snapshot update of Yul output due to branch emission changes.
crates/codegen/src/yul/emitter/control_flow.rs	Fixes loop/control-flow emission to handle complex loop headers and avoid incorrect join detection.

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Copilot · 2026-02-28T05:35:17Z

crates/parser/src/parser/expr.rs

        parser.set_newline_as_trivia(false);
+        let is_or = parser.current_kind() == Some(SyntaxKind::Pipe2);
+        let msg = "`||` cannot be mixed with `let` conditions in this position";
        let (_, rbp) = infix_binding_power(parser).unwrap();
+        let saw_let_before = self
+            .condition_state
+            .as_ref()
+            .is_some_and(|state| state.borrow().saw_let);
+        let mut reported = false;
+        if self.allow_let_expr && is_or && saw_let_before {
+            parser.error_msg_on_current_token(msg);
+            reported = true;
+        }
        bump_bin_op(parser);
-        parse_expr_with_min_bp(parser, rbp, false)
+        parse_expr_with_min_bp(
+            parser,
+            rbp,
+            false,
+            self.allow_let_expr,
+            self.condition_state.clone(),
+        )?;
+
+        if self.allow_let_expr
+            && is_or
+            && !reported
+            && self
+                .condition_state
+                .as_ref()
+                .is_some_and(|state| state.borrow().saw_let)
+        {
+            parser.error(msg);
+        }


In BinExprScope::parse, when || is followed by a let condition on the RHS (e.g. ready || let Some(x) = ...), the diagnostic is currently emitted via parser.error(msg) after parsing the RHS. That attaches a zero-length range at the next token (often {), rather than highlighting the || operator. Consider detecting let on the RHS upfront (e.g. via lookahead to the next non-trivia token) and using error_msg_on_current_token on the || token so the error location is consistent and points at the operator.

chatgpt-codex-connector bot reviewed Feb 25, 2026

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crates/hir/src/core/lower/expr.rs Outdated Show resolved Hide resolved

sbillig marked this pull request as draft February 25, 2026 06:16

sbillig added 3 commits February 26, 2026 20:13

implement if-let/while-let support

7fefefe

tree-sitter: if-let/while-let

3b916a5

use expected type for if type checking

9605165

sbillig force-pushed the if-let branch from 11593f2 to 9605165 Compare February 27, 2026 19:37

sbillig marked this pull request as ready for review February 27, 2026 19:47

fix if-let lowering and ctfe binding scope

e076e6c

sbillig requested a review from Copilot February 28, 2026 05:29

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`if let` and `while let` support#1282

`if let` and `while let` support#1282
sbillig wants to merge 4 commits intoargotorg:masterfrom
sbillig:if-let

sbillig commented Feb 25, 2026 •

edited

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sbillig commented Feb 25, 2026 •

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