Reject duplicate function parameters#876
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Great， does the same problem exist in cpp? |
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CPP is fine |
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…ontexts (#1011) ## Motivation go-jsonnet issue #873 reports that `(function(x, x, x) x)(null, 3, 2)` silently returns `2` instead of rejecting duplicate parameter names. sjsonnet already rejected duplicates in function expressions, but the error message was misleading in local bindings and object methods (e.g. "Expected \")\"" or "Expected \":\""). ## Modification The `params` parser correctly detects duplicates via `flatMapX` + `Fail`. However, in `bind` (`local f(x,x)=...`) and `field` (`{f(x,x):...}`), the optional group `.?` around `params` swallowed the "no duplicate parameter" error and backtracked, producing misleading errors. Two changes fix this: 1. In `field()`: added `~/` (cut) after `"("` to commit to the params path once `"("` is matched: `"(" ~/ params(...) ~ ")"`. 2. In `params()`: set `ctx.cut = true` programmatically when a duplicate is detected, preventing outer `.?` operators from swallowing the error. Also captures `Pos` for each parameter to position the error at the duplicate parameter name (not at the closing paren). ## Result All duplicate parameter contexts now produce the correct error `"Expected no duplicate parameter: x"` with accurate position info: - `(function(x, x, x) x)` -> ParseError (already worked) - `local f(x, x) = x` -> ParseError (was `"Expected )"`) - `{ f(x, x): x }` -> ParseError (was `"Expected :"`) - `{ local f(x, x) = x }` -> ParseError (was `"Expected )"`) - Nested bindings also fixed as a bonus. Tests pass on Scala 3.3.7, 2.13.18, 2.12.21. ## References - google/go-jsonnet#873 ## Cross-implementation comparison: Duplicate function parameters | Implementation | Detection Phase | All Contexts Covered | Error Message Example | |---|---|---|---| | **sjsonnet (this fix)** | Parse time | ✅ All 4 contexts | `Expected no duplicate parameter: x` | | **cpp-jsonnet** | Static analysis (post-parse) | ✅ All 4 (via desugaring) | `Duplicate function parameter: x` | | **go-jsonnet** (master) | ❌ None | ❌ Bug — silently accepts | N/A — last argument wins silently | | **go-jsonnet** ([PR #876](google/go-jsonnet#876), unmerged) | Parse time | ✅ All 4 | `Duplicate function parameter: a` / `Duplicate method parameter: x` | | **jrsonnet** | Static analysis (post-parse) | ✅ All 4 (via desugaring) | `local is already defined in the current frame: x` | ### Behavior by test case | Test Case | sjsonnet (fix) | cpp-jsonnet | go-jsonnet | jrsonnet | |---|---|---|---|---| | `(function(x, x, x) x)(null, 3, 2)` | ✅ ParseError | ✅ StaticError | ❌ Returns `2` | ✅ StaticError | | `local f(x, x) = x; f(1, 2)` | ✅ ParseError | ✅ StaticError | ❌ Accepted | ✅ StaticError | | `{ f(x, x): x }.f(1, 2)` | ✅ ParseError | ✅ StaticError | ❌ Accepted | ✅ StaticError | | `{ local f(x, x) = x, a: f(1, 2) }` | ✅ ParseError | ✅ StaticError | ❌ Accepted | ✅ StaticError | ### Key differences - **Detection timing**: sjsonnet and go-jsonnet (PR #876) detect at parse time; cpp-jsonnet and jrsonnet detect during a separate static analysis pass after parsing. - **Error message specificity**: go-jsonnet PR #876 distinguishes "function parameter" vs "method parameter"; cpp-jsonnet uses "function parameter" uniformly (methods desugar to functions before the check). - **Position accuracy**: sjsonnet points to the duplicate parameter name; cpp-jsonnet points to the entire function AST node. - **go-jsonnet master** has a known bug ([issue #873](google/go-jsonnet#873)) where duplicate parameters are silently accepted with "last argument wins" semantics.
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Rejects duplicate parameter names while parsing function and method parameter lists.
Previously, go-jsonnet accepted inputs like:
That makes argument/default handling ambiguous and differs from other Jsonnet implementations, which reject duplicate parameters.
This change tracks parameter names while parsing and returns a static error when the same name appears twice. It covers normal functions, local function sugar, and object methods.
Fixes #873.
Testing:
go test ./internal/parsergo test ./...