feat(kdl): rename keywords for clarity (alias, as, var, where)

[pesap]

Summary

Rename four KDL keywords for clarity and consistency, with backwards compatibility via deprecation warnings.

Parent: #176
Blocked by: #178

Keyword Changes

Before	After	Purpose
map X from="col"	alias X column="col"	Data column rename
set X alias=g	set X as=g	Set shorthand
control x lower=0	var x lower=0	Decision variable
filter { cond }	where { cond }	Set subsetting

Acceptance Criteria

• Parser accepts alias X column="col"; deprecates map X from="col"
• Parser accepts set X as=g; deprecates set X alias=g
• Parser accepts var x lower=0; deprecates control x lower=0
• Parser accepts where { cond }; deprecates filter { cond }
• All deprecated forms emit warnings with migration hints (via feat(kdl): add deprecation warning infrastructure #178)
• AST output is identical for old and new syntax
• Test: new syntax parses to correct AST
• Test: old syntax parses to same AST + emits deprecation warning
• Test: mixed old/new syntax in same file works

Implementation Notes

Location: crates/arco-kdl/src/source/parser.rs

Pattern per keyword:

match child.name().value() {
    "alias" => { /* new syntax */ }
    "map" => {
        context.warn(Deprecation::new("map", "alias", child.span()));
        /* parse as alias */
    }
    // ...
}

• AFK — straightforward parser additions with clear pattern

TDD Implementation Plan

Prerequisites

• Complete feat(kdl): add deprecation warning infrastructure #178 (deprecation warning infrastructure)

RED/GREEN Cycles

Cycle 1: var keyword (simplest, isolated)

RED: Test that var x lower=0 {...} parses to same AST as control

#[test]
fn var_keyword_parses_as_control() {
    let new_syntax = r#"model M { var x lower=0 { index a } minimize O { x[a] } }"#;
    let old_syntax = r#"model M { control x lower=0 { index a } minimize O { x[a] } }"#;
    // Assert both produce identical ControlDecl
}

GREEN: Add "var" => arm in parse_model() (line 85) calling parse_control()

Cycle 2: control deprecation warning

RED: Test that control emits deprecation warning

#[test]
fn control_keyword_emits_deprecation() {
    let text = r#"model M { control x { index a } minimize O { x[a] } }"#;
    // Assert warning contains "control", "var", migration hint
}

GREEN: Add deprecation emission before parse_control() call for "control" arm

Cycle 3: alias keyword (data block)

RED: Test alias X column="col" parses as MapDecl

#[test]
fn alias_keyword_parses_in_data_block() {
    let text = r#"data D source="f.csv" { alias X column="name" }"#;
    // Assert MapDecl with name="X", source="name"
}

GREEN: Add "alias" => arm in parse_data() (line 133) with column property

Cycle 4: map deprecation warning

RED: Test map emits deprecation
GREEN: Add deprecation to "map" arm

Cycle 5: set as= property

RED: Test set X as=g parses with alias "g"

#[test]
fn set_as_property_parses() {
    let text = r#"set X as=g"#;
    // Assert SetDecl has alias = Some("g")
}

GREEN: Add .get("as") fallback in parse_set() (line 255)

Cycle 6: set alias= deprecation

RED: Test alias= emits deprecation
GREEN: Check for alias= property and emit warning

Cycle 7: where keyword (set filter)

RED: Test where { cond } parses as filter

#[test]
fn where_keyword_parses_as_filter() {
    let text = r#"set thermal { in gen; where { type == "thermal" } }"#;
    // Assert filter_expression is set
}

GREEN: Add "where" => arm in:

• parse_set() (line 233)
• parser_helpers.rs (lines 54, 94)
• surface.rs (lines 10, 121)

Cycle 8: filter deprecation

RED: Test filter emits deprecation
GREEN: Add deprecation to all "filter" arms

Cycle 9: Mixed syntax integration

RED: Test file with mix of old/new syntax
GREEN: Should already pass if cycles 1-8 are complete

Files to Modify

• crates/arco-kdl/src/source/parser.rs
• crates/arco-kdl/src/source/parser_helpers.rs
• crates/arco-kdl/src/source/surface.rs

Acceptance Verification

cargo test -p arco-kdl
cargo clippy -p arco-kdl -- -D warnings