fix: support braceless predicates matching Go expr-lang behavior by jdx · Pull Request #23 · jdx/expr.rs

jdx · 2026-02-10T11:52:01Z

Summary

In Go expr-lang, predicates like filter(arr, # > 2) work without braces. Our PEG parser requires braces because # gets consumed as an expr argument before the predicate rule can match.
This fix detects when the last argument to a function contains # references and promotes it to the predicate position at the AST level.
The promotion only triggers when there are 2+ args to avoid incorrectly affecting nested calls like len(#) inside sortBy(arr, {len(#)}).

Test plan

Added tests for braceless predicates: filter(0..9, # % 2 == 0), filter([1, 2, 3], # > 1), map([1, 2, 3], # * 2)
Verified existing sortBy tests with {len(#)} still pass (no regression)
All 94 tests pass

🤖 Generated with Claude Code

Note

Medium Risk
Changes how function-call ASTs are constructed by reclassifying certain trailing arguments as predicates, which could subtly alter parsing/semantics for edge-case expressions. Scope is limited to a hardcoded set of predicate-accepting functions and is covered by new regression tests.

Overview
Enables Go expr-lang–compatible braceless predicates like filter(arr, # > 2) and pipe forms like arr | filter(# > 2) by promoting the last argument to a function predicate when it references # and no explicit {...} predicate was parsed.

Adds contains_hash_ident traversal on Node/PostfixOperator and gates promotion behind a hardcoded allowlist of predicate-capable functions to avoid changing behavior for non-predicate calls and nested # usage; expands tests to cover braceless, piped, and nested-predicate regression cases.

^{Written by Cursor Bugbot for commit 2f34560. This will update automatically on new commits. Configure here.}

In Go expr-lang, predicates like `filter(arr, # > 2)` work without braces around the predicate expression. Our PEG parser requires braces because `#` gets consumed as an `expr` argument before the `predicate` rule has a chance to match. This fix detects when the last argument to a function contains `#` and promotes it to the predicate position at the AST level. The promotion only triggers when there are 2+ args to avoid incorrectly affecting nested calls like `len(#)` inside `sortBy(arr, {len(#)})`. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gemini-code-assist · 2026-02-10T11:52:17Z

Summary of Changes

Hello @jdx, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the expression language parser to support a more flexible syntax for function predicates. By automatically detecting and promoting braceless predicates containing the # variable, it improves user experience and ensures consistency with the behavior of Go expr-lang, making expressions like filter(arr, # > 2) valid without requiring explicit braces.

Highlights

Braceless Predicate Support: Implemented support for braceless predicates in function calls, such as filter(arr, # > 2), aligning the behavior with Go expr-lang.
Hash Identifier Detection: Introduced a contains_hash_ident method on the Node enum to recursively detect # variable references within an Abstract Syntax Tree (AST) node.
Predicate Promotion Logic: Modified the AST construction logic to automatically promote the last argument of a function call to a predicate if it contains a # reference, no explicit predicate was provided, and there are at least two arguments.

Changelog

src/ast/node.rs
- Added contains_hash_ident method to Node for recursive checking of # identifier presence.
- Modified From<Pair<'_, Rule>> for Node to implement predicate promotion logic for function calls.
src/test.rs
- Added new test cases to validate the parsing and evaluation of braceless predicates in filter and map functions.

Activity

Added tests for braceless predicates: filter(0..9, # % 2 == 0), filter([1, 2, 3], # > 1), map([1, 2, 3], # * 2).
Verified existing sortBy tests with {len(#)} still pass, ensuring no regressions.
Confirmed that all 94 tests pass after the changes.
The pull request was generated with Claude Code.

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Code Review

This pull request introduces support for braceless predicates to align with Go expr-lang behavior, which is a great enhancement for usability. The implementation correctly identifies when to promote an argument to a predicate by checking for the # reference. The logic is sound and well-tested. I have one suggestion to make the code for promoting the argument more concise and readable.

gemini-code-assist · 2026-02-10T11:54:10Z

src/ast/node.rs

+                if predicate.is_none() && args.len() >= 2 {
+                    if let Some(last) = args.last() {
+                        if last.contains_hash_ident() {
+                            let last = args.pop().unwrap();
+                            predicate = Some(Box::new(Program {
+                                lines: Vec::new(),
+                                expr: last,
+                            }));
+                        }
+                    }
+                }


This block can be made more concise by combining the conditions into a single if statement. The if let is redundant since args.len() >= 2 guarantees args.last() is Some. Using unwrap() is safe here due to the length check.

if predicate.is_none() && args.len() >= 2 && args.last().unwrap().contains_hash_ident() { let last = args.pop().unwrap(); predicate = Some(Box::new(Program { lines: Vec::new(), expr: last, })); }

src/ast/node.rs

- Use a whitelist of predicate-accepting functions (filter, map, sortBy, etc.) instead of relying on arg count heuristic. This prevents the promotion from incorrectly firing on nested multi-arg functions like indexOf("abc", #) inside braced predicates. - Lower threshold from args.len() >= 2 to >= 1 so pipe syntax works: `arr | filter(# > 2)` where the array arrives at runtime via pipe. - Fix contains_hash_ident to recurse into PostfixOperator inner nodes (Index, Default, Ternary, Pipe) which can contain # references. - Add tests for pipe + braceless predicates and nested func in predicate. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cursor

Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Bugbot Autofix is ON, but a Cloud Agent failed to start.}

src/ast/node.rs

contains_hash_ident was recursing into Node::Func predicates, but # inside a function's predicate is bound to that function's iteration — not a free reference for outer promotion. For example, in map(arr1, any(arr2, {# > 0})), the inner any's # is bound, so it should not cause any(...) to be promoted as map's predicate. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

…8081) ## Summary - Flutter's Google API returns releases in newest-first order, which causes `mise install flutter` to resolve to an old version (3.22.1) instead of the latest (3.38.x) - Switch from `version_json_path` to `version_expr` with `sortVersions()` to ensure proper ascending semver order - Adds a unit test for the Flutter version_expr parsing Fixes #7863 (comment) Also submitted jdx/expr.rs#23 to fix braceless predicate parsing in expr.rs (Go expr-lang compatibility), which is why this PR uses `{#.channel == "stable"}` with braces. ## Test plan - [x] Unit test `test_parse_flutter_with_version_expr` verifies correct filtering and sorting - [x] All existing tests pass - [x] Linting passes 🤖 Generated with [Claude Code](https://claude.com/claude-code)  --- > [!NOTE] > **Low Risk** > Low risk: registry config change and a new unit test; behavior change is limited to how Flutter versions are extracted/sorted from the upstream JSON. > > **Overview** > Fixes Flutter version resolution by switching the registry backend from `version_json_path` to a `version_expr` that filters `stable` releases and applies `sortVersions()` so installs pick the latest stable version. > > Adds a unit test (`test_parse_flutter_with_version_expr`) to validate the expr-based filtering/sorting behavior against Flutter-style JSON. > > <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 9af283d. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>  Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

…dx#8081) ## Summary - Flutter's Google API returns releases in newest-first order, which causes `mise install flutter` to resolve to an old version (3.22.1) instead of the latest (3.38.x) - Switch from `version_json_path` to `version_expr` with `sortVersions()` to ensure proper ascending semver order - Adds a unit test for the Flutter version_expr parsing Fixes jdx#7863 (comment) Also submitted jdx/expr.rs#23 to fix braceless predicate parsing in expr.rs (Go expr-lang compatibility), which is why this PR uses `{#.channel == "stable"}` with braces. ## Test plan - [x] Unit test `test_parse_flutter_with_version_expr` verifies correct filtering and sorting - [x] All existing tests pass - [x] Linting passes 🤖 Generated with [Claude Code](https://claude.com/claude-code)  --- > [!NOTE] > **Low Risk** > Low risk: registry config change and a new unit test; behavior change is limited to how Flutter versions are extracted/sorted from the upstream JSON. > > **Overview** > Fixes Flutter version resolution by switching the registry backend from `version_json_path` to a `version_expr` that filters `stable` releases and applies `sortVersions()` so installs pick the latest stable version. > > Adds a unit test (`test_parse_flutter_with_version_expr`) to validate the expr-based filtering/sorting behavior against Flutter-style JSON. > > <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 9af283d. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup>  Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

jdx mentioned this pull request Feb 10, 2026

fix(install): use version_expr for Flutter to fix version resolution jdx/mise#8081

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jdx force-pushed the fix/predicate-parsing branch from 0c01dc4 to a6bebf4 Compare February 10, 2026 12:13

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jdx merged commit a85e62e into main Feb 10, 2026
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jdx deleted the fix/predicate-parsing branch February 10, 2026 12:42

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fix: support braceless predicates matching Go expr-lang behavior#23

fix: support braceless predicates matching Go expr-lang behavior#23
jdx merged 3 commits intomainfrom
fix/predicate-parsing

jdx commented Feb 10, 2026 •

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