Plan analysis: skip Row Estimate Mismatch on unexecuted operators, skip engine functions in the TVF rule (#4522, #4525)

[erikdarlingdata]

Fixes #4522
Fixes #4525
Part of #4511

Why

Two of the plan analyzer's rules fired when they shouldn't have.

Rule 5 (Row Estimate Mismatch) checked only that an operator had actual stats and a nonzero row estimate. An operator in a branch that never ran (one side of a concatenation, an outer join's unreached inner side) returns 0 rows because it never executed — that zero says nothing about whether the estimate was right. The rule warned anyway.

Rule 23 (Table-Valued Function) fired on every operator with LogicalOp == "Table-valued function", including the engine's own functions: STRING_SPLIT, OPENJSON, GENERATE_SERIES, and every DMV/DMF. Its advice (rewrite as an inline function, or stage rows in a #temp table) is for user-written multi-statement TVFs, which have no statistics. The engine's functions aren't user code and the advice doesn't apply to them.

What changes

• PlanAnalyzer.cs rule 5: adds node.ActualExecutions > 0 to the condition, and removes the now-unreachable ActualExecutions > 0 ? ActualExecutions : 1 fallback (the divisor is always the real execution count once the new guard runs first).
• PlanModels.cs: adds PlanNode.SchemaName, alongside the existing DatabaseName.
• ShowPlanParser.cs: sets SchemaName from the parsed Object element, next to where DatabaseName is already set.
• PlanAnalyzer.cs rule 23: skips an operator whose Object has neither a database nor a schema — how the engine's own functions appear in the plan XML. A user-written function always has both.

This mirrors erikdarlingdata/PerformanceStudio@cc18844 and erikdarlingdata/PerformanceStudio@de1cac6 (#4522) and erikdarlingdata/PerformanceStudio#584 (#4525), adapted only in that PerformanceMonitor has no AnalyzerConfig, so there's no cfg.IsRuleDisabled(...) guard to preserve.

Test plan

New tests: Darling.Tests.PlanSync4522Tests, Darling.Tests.PlanSync4525Tests. Both build a synthetic actual-plan XML (dbo.t, [db]) and run it through ShowPlanParser.Parse + PlanAnalyzer.Analyze — the product's own parse-then-analyze path, not a hand-built PlanNode.

• PlanSync4522Tests.Rule05_OperatorThatNeverExecuted_IsNotAnEstimateMismatch: runtime RED on dev (Assert.False() Failure: Expected: False, Actual: True), and a still-warns mirror.
• PlanSync4525Tests: the two rule-23 facts (an engine STRING_SPLIT → no warning; [db].[dbo] user function → still warns) use only existing members. The engine fact is a runtime RED on dev (Assert.DoesNotContain() Failure: Filter matched in collection, the TVF warning present). Parser_SetsSchemaName_NextToDatabaseName asserts the new PlanNode.SchemaName member, so it is a compile-only RED on dev.
• Mutations, each reverted: dropping node.ActualExecutions > 0 from rule 5 fails the rule-5 fact; dropping !isEngineFunction from rule 23 fails the engine fact.
• Run: the new classes plus the plan-analysis classes (ShowPlanParserCondAndMultiplePlanTests, the ActualPlan* classes, QueryModificationDetectorTests, ReproScriptBuilderHardeningTests, DarlingAnalysisPipelineTests, DarlingMcpPlanToolsSurfaceAndSqlTests, McpPlanAnalysisEnvelopeTests, SerialLoopStoreSizeSourceTests, TsqlConventionGuardTests, DocCommentHygieneTests): Total: 234, Failed: 0. The live-Postgres plan-tool class runs in CI. Lite.Tests builds; its plan classes run on Windows only.

CHANGELOG

SECTION: Fixed
ENTRY: - Plan analysis no longer flags an unexecuted operator as a row estimate mismatch, and stops recommending a rewrite for the engine's own table-valued functions (STRING_SPLIT, OPENJSON, GENERATE_SERIES, DMVs/DMFs) ([#4542]) - Rule 5 previously warned about a 0-row estimate mismatch on any operator whose branch never ran; it now requires ActualExecutions > 0. Rule 23 previously warned on every table-valued function operator; it now skips one whose object has neither a database nor a schema, which is how the engine's own functions appear.
REF: [#4542]: #4542