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feat(compiler): implement ternary conditional expressions from semantics to C codegen - #62

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SuperIceCN merged 7 commits into
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feat/frontend/ternary-expr
Aug 20, 2026
Merged

feat(compiler): implement ternary conditional expressions from semantics to C codegen#62
SuperIceCN merged 7 commits into
masterfrom
feat/frontend/ternary-expr

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@SuperIceCN SuperIceCN commented Aug 20, 2026

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Summary

Implement GDScript ternary conditional expressions (value1 if condition else value2, including right-nested forms) across the full pipeline: frontend shared semantics, compile gate lift, CFG construction, body lowering, and C backend execution.

What changed

  • Parser/AST baseline: froze parse shape and associativity tests for ConditionalExpression (FrontendConditionalParseBehaviorTest); no parser changes needed.
  • Shared semantics (FrontendExpressionSemanticSupport): ternary type merge contract — condition resolved with expectedType=null; both arms resolved against outer expectedType; merge via bidirectional determineFrontendBoundaryDecision, falling back to Variant; FAILED arm re-owns the root FrontendExpressionType (binary-style); void arm rejected at root, void + Variant degrades to DYNAMIC(Variant).
  • CFG construction (FrontendCfgGraphBuilder / FrontendCfgGraph): dual-context expansion — value-context ternaries produce branch-result MergeValueItem with anchor-typed slots; condition-context ternaries expand as pure control flow with zero merge items; BranchNode.conditionValueId must be a temp, never a merge id.
  • Merge contracts (MergeValueItem, FrontendBodyLoweringSupport, FrontendSequenceItemInsnLoweringProcessors): merge_write re-derives via materializeFrontendBoundaryValue; graph-wide merge-of-merge widening validation; merge slot lifetime identical to cfg_tmp_* (declare + __prepare__ default-construct + per-arm destroy-then-write + __finally__ destroy) so the backend needs no cfg_merge_ special cases.
  • Compile gate (FrontendCompileCheckAnalyzer): removed the explicit ConditionalExpression intercept; it now falls into the default compile-surface walk with exact-range dedup.
  • Docs: promoted the plan into the long-term fact source frontend_conditional_expression_implementation.md; synced 12 referencing docs and README support lists (ternary, plus for/lambda entries).
  • Tests/e2e: 9 ternary/ script+validation fixture pairs wired into GdScriptUnitTestCompileRunnerTest, covering same-type, int/float merge, nesting, object ancestor merge, null arm, non-bool condition, statement position, condition context, and destroyable arms.

Why

Ternary conditionals were the last common expression form explicitly blocked at the compile gate. Godot semantics (single-arm evaluation, type merge with boundary conversion) map naturally onto the existing branch-result merge infrastructure, so the implementation reuses MergeValueItem instead of adding backend-specific merge handling.

Affected packages/files

  • gd.script.gdcc.frontend.sema.analyzer (+ support): FrontendCompileCheckAnalyzer, FrontendExpressionSemanticSupport, FrontendBodyOwnerProcedures
  • gd.script.gdcc.frontend.lowering (+ cfg, cfg.item, pass.body): FrontendCfgGraphBuilder, FrontendCfgGraph, MergeValueItem, FrontendBodyLoweringSupport, FrontendSequenceItemInsnLoweringProcessors
  • Tests: parse behavior, sema support, compile gate, CFG builder/graph, lowering passes, e2e runner + ternary/ fixtures
  • Docs: doc/module_impl/frontend/* (13 files), README.md, README.zh-CN.md

Validation

  • .\gradlew.bat test --tests "gd.script.gdcc.frontend.*" --no-daemon --console=plain — all frontend tests green (1276)
  • pwsh -ExecutionPolicy Bypass -File script/run-gradle-targeted-tests.ps1 -Tests FrontendCompileCheckAnalyzerTest,FrontendCfgGraphBuilderTest,FrontendCfgGraphTest,FrontendLoweringBuildCfgPassTest,FrontendLoweringBodyInsnPassTest,GdScriptUnitTestCompileRunnerTest
  • .\gradlew.bat clean build --no-daemon --console=plain — 3207 tests; only 5 failures from a Windows DLL file-lock on unrelated engine tests (AccessDeniedException on construct_lambda_engine_debug_x86_64.dll), which pass when re-run individually
  • Generated ternary_destroyable_arms/entry.c inspected: merge slot declared, default-constructed in __prepare__, destroy-then-write per arm, destroyed in __finally__

Result: BUILD SUCCESSFUL (targeted); full build green except environment-only DLL lock flakes.

Risks / Notes

  • No constant folding or flow-sensitive type narrowing for ternary arms (matches Godot MVP scope).
  • No INCOMPATIBLE_TERNARY diagnostic; incompatible merges fall back to Variant like other binary merges.
  • Condition arm is never type-narrowed by the merge result; BranchNode.conditionValueId reuse of a merge id is forbidden by contract and tests.

Key behaviors covered

  • Right-associative nesting: a if c1 else b if c2 else c
  • Boundary conversion on mixed arms (int/float via c_int_to_float)
  • Object arms merged to common ancestor; null arm yields nullable/object-or-null merge
  • Non-bool conditions truthiness-evaluated; statement-position ternaries discard the merge value
  • Destroyable arm values get full ownership lifecycle through the merge slot

Diff stats

  • 54 files changed, 2956 insertions(+), 167 deletions(-)

Breaking changes

  • None

Related docs

  • doc/module_impl/frontend/frontend_conditional_expression_implementation.md
  • doc/module_impl/frontend/frontend_lowering_cfg_pass_implementation.md

@Iridium-Zero
docs(frontend): add conditional expression implementation plan for te…
7f7909a 
…rnary operator

- Define scope and Godot-aligned semantics for ternary expressions with right-associative nesting
- Specify shared type inference and merged-type resolution with diagnostic ownership
- Outline CFG construction for value and condition contexts with merge contract refinements
- Detail staged implementation phases and testing matrix from parsing to end-to-end verification
@Iridium-Zero
test(frontend): freeze ternary parse behavior and close Phase 0 baseline
7808a9c 
- Anchor field mapping, right-associative nesting, and lowest-precedence binding at the parser boundary
- Cover parenthesized associativity overrides, statement-position usage, and tolerant incomplete-syntax handling
- Keep semantic analysis, CFG construction, and compile-gate surfaces unchanged for the baseline step
- Align implementation plan status and acceptance criteria with the landed characterization
@Iridium-Zero
feat(frontend): implement semantic type inference for ternary conditi…
11feb20 
…onal expressions

- Resolve ternary arms with contextual expected-type propagation and merge via the shared boundary compatibility matrix
- Handle runtime-open, void, and incompatible arm pairs with ordered fallback to dynamic or Variant semantics
- Promote conditional expressions from deferred to fully typed with right-associative nesting support
- Preserve diagnostic ownership so arm failures re-emit at the conditional root with precise source ranges
- Record phase completion in implementation plan and expand coverage for merging, contextuality, and error isolation
@Iridium-Zero
feat(frontend): refine merge-slot contracts for ternary conditional l…
e1fdc78 
…owering

- Anchor merge slot types at the shared expression result instead of per-arm source values
- Route merge writes through the unified typed-boundary materialization as a re-derive consumer
- Allow merge-of-merge sources across sequences while keeping dangling and mixed sources rejected
- Update lowering and frontend rule documentation to reflect the refined contracts and Phase 2 completion
- Add coverage for anchor typing, nested merge sources, and fail-fast edges with and/or LIR shape preserved
@Iridium-Zero
feat(frontend): implement CFG construction for ternary conditional ex…
5975ae8 
…pressions

- Build value-context ternaries via shared branch-result merge with arm-private temps and merge-of-merge continuation
- Expand condition-context ternaries as pure control flow reusing short-circuit branching without merge values
- Preserve branch-local condition temps, anchor-typed merge slots, and preferred result identity for initializers
- Clarify lowering and frontend gate docs to mark CFG contracts complete with compile-gate still pending
- Expand coverage for nesting, associativity, short-circuit conditions/arms, and condition embeddings
@Iridium-Zero
feat(frontend): lift compile gate for ternary conditional expressions…
9007ccc 
… and complete integration validation

- Remove explicit compile block and route ternary expressions through normal type resolution and CFG lowering
- Expand focused coverage across compile checks, analysis passes, CFG shape, and body lowering for value, condition, and statement contexts
- Add end-to-end suites covering mixed-type merges, nested associativity, object and null merges, truthiness, and discard semantics
- Verify destroyable merge-slot lifecycle matches existing temporary and local slot ownership contracts
- Synchronize implementation plans and frontend rule documentation to reflect the completed surface
@Iridium-Zero
docs(frontend): promote ternary conditional plan to implementation re…
a539bf3 
…cord

- Graduate conditional expression plan into maintained implementation documentation after full surface closure
- Retire transitional phase markers and interim compile-gate notes
- Synchronize cross-document references to the new implementation source of truth
Copilot AI lite review requested due to automatic review settings August 20, 2026 13:22
Copilot AI reviewed Aug 20, 2026

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@SuperIceCN
SuperIceCN merged commit 355b8f3 into master Aug 20, 2026
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@SuperIceCN @Iridium-Zero