feat(code-graph): extract package-level var and const in go

Bartłomiej Piekarzrequested to merge
bartekp854/knowledge-graph:fix-671-go-var-const into main

What does this MR do and why?

Extracts package-level var and const declarations in Go as structural Definition nodes in the knowledge graph.

Previously, the Go code indexer handled var_spec and const_spec strictly as local scope bindings. While this enabled internal reference resolution, it prevented exported constants and sentinel errors (e.g. var ErrNotFound = errors.New("not found")) from being emitted as persistent Definition nodes.

This MR adds new scope rules to the Go DSL that elevate package-level variables and constants to graph entities.

Related Issues

Closes #671 (closed)

Testing

Verified by adding a new integration test fixture crates/integration-tests-codegraph/fixtures/go/var_const.yaml) which asserts that var and const definitions are successfully extracted. The changes were validated locally by runnin cargo nextest run -p integration-tests-codegraph.

Performance Analysis

This MR shouldn't introduce any performance regression. The extraction of these declarations utilizes the existing tree-sitter AST visitation pass without introducing new pipeline stages or heavy allocations.

  • This merge request does not introduce any performance regression. If a performance regression is expected, explain why.

Agent context — long-form analysis, file-by-file walkthroughs, profiler output, alternatives considered

Implementation Details:

  • Added var_spec and const_spec to the scopes array in crates/code-graph/src/v2/langs/generic/go.rs.
  • var_spec is mapped to DefKind::Property and const_spec is mapped to DefKind::EnumEntry.
  • Both scopes use no_scope() since variable declarations do not introduce new lexical blocks for children.
  • Applied the structural predicate .when(!ancestor_is(&["function_declaration", "method_declaration", "func_literal"])) to ensure that only package-level variables are elevated to the graph. This successfully prevents local function variables from cluttering the database as definitions.
  • Tree-sitter parses grouped declarations (e.g. var ( A = 1 \n B = 2 )) as individual var_spec nodes under a parent var_declaration. Because our scope rules target var_spec directly, they naturally handle grouped package declarations without requiring any custom flattening logic.

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