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fix(cli): rescale count-derived money when --max-instances truncates a row - #1846
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…a row ApplyInstanceLimit cut a recommendation's Count to fit the --max-instances budget but copied the struct wholesale, so every whole-row money figure survived at its full pre-cap value. A row entering with Count=100 and EstimatedSavings=600 left as Count=10 with EstimatedSavings=600, a 10x overstatement for that row. The figure flows into the run summary, the purchase report and the CSV, so an operator saw a capped run promising savings it cannot deliver. Affects both the default and the --input-csv path. Truncated rows are now scaled by the discrete count ratio via common.ScaleRecommendationCosts, the helper every other sizing path (ApplyCoverage, ApplyTargetCoverage, family-NU) already used. Only the extensive fields scale: SavingsPercentage and BreakEvenMonths are ratios of figures that scale together, RecommendedCount is a frozen record of the provider's proposal, and the usage signals describe observed demand rather than what we buy. A nil RecurringMonthlyCost stays nil, since absent is not the same claim as zero. A non-positive Count can never enter the truncation branch, so the ratio never divides by a zero or negative denominator. ScaleRecommendationCosts now also scales SavingsPlanDetails.HourlyCommitment, which was duplicated at its two existing call sites and missing at this new third one. An SP commitment is dollar-denominated, and --override-count sets Count on SP recs without discriminating by commitment type, so an SP can reach the cap at a truncatable count; scaling its costs while leaving its commitment whole would produce an internally inconsistent row. Closes #1830
- Use math.IsNaN/math.IsInf instead of a hand-rolled float classifier that misreported large-but-finite values as infinite. - Hoist the *SavingsPlanDetails assertion in applyTargetCoverageSP so the type is asserted once rather than three times. The zero-commitment and wrong-type guards are reordered, which is behaviour-equivalent: a non-SP Details reached the warning either way, and an SP with a non-positive commitment reached the skip either way. - Enumerate the count-linear non-money fields ScaleRecommendationCosts deliberately leaves alone (ProjectedCoverage / ProjectedUtilization, DataWarehouseDetails.NumberOfNodes) so the docstring's completeness claim is honest. - Drop the self-contradicting half of the sortBySavingsPerInstance comment: rate invariance makes a post-cap sort harmless, not useful, and the ordering requirement is unchanged.
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Included review availability: 0 reviews are currently available. Based on recent review activity, included reviews refill at 2 per hour. 📝 WalkthroughWalkthroughThe change scales count-derived costs and Savings Plan hourly commitments when recommendations are truncated. It validates Savings Plan details, preserves pointer behavior, and adds tests for scaling, immutability, edge cases, typed-nil details, and aggregate totals. ChangesRecommendation scaling
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to The change rescales count-derived money values when instance limits truncate a recommendation, keeping summaries and purchase reports accurate; no actionable merge-blocking risk remains after normal checks and review. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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In `@pkg/common/types.go`:
- Around line 320-324: Handle typed-nil SavingsPlanDetails safely across
pkg/common/types.go lines 320-324, cmd/helpers.go lines 152-155, and
cmd/helpers.go lines 433-443: in ScaleRecommendationCosts, require details !=
nil before copying and scaling; in the caller, only scale non-nil details and
otherwise retain the existing unscaled warning path; in applyTargetCoverageSP,
reject nil details before reading HourlyCommitment. Add regression coverage for
an interface containing (*common.SavingsPlanDetails)(nil).
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cmd/helpers.gocmd/helpers_instance_limit_rescale_test.gocmd/multi_service_csv_cap.gocmd/multi_service_max_instances_test.gopkg/common/types.go
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The misspell linter enforces American spelling and reddened the Lint Code job on "neighbouring".
An interface holding (*SavingsPlanDetails)(nil) satisfies a type assertion to *SavingsPlanDetails with ok == true and yields a nil pointer, so the comma-ok alone was not a guard. Three sizing sites then dereferenced it: - ScaleRecommendationCosts copied *details - applyCoverage's SP branch discarded the pointer and called the helper, which panicked inside - applyTargetCoverageSP read details.HourlyCommitment for its no-signal guard, before any nil check A malformed recommendation must degrade and warn, not crash. Panicking partway through a capped run leaves the operator with no report at all rather than a degraded one, which is the opposite of what the rest of this change is careful about on a money path. The two cmd sites now take the existing warn-and-pass-through-unscaled path, which is what a rec whose commitment cannot be scaled should do. The helper leaves a nil Details exactly as it found it rather than substituting a fabricated zero-value commitment, and still scales the cost fields, which do not depend on Details. The warning text now says "missing or unexpected" since a typed nil is neither an absent Details nor a wrong type. Regression tests use an interface explicitly holding a typed nil; a plain nil interface fails the assertion and takes a different path, so only the typed form reproduces the crash. A sentinel test pins that Go semantic so the guards cannot start passing vacuously.
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What
ApplyInstanceLimittruncated a recommendation'sCountto fit the--max-instancesbudget but copied the struct wholesale, so every whole-row money figure survived at its full pre-cap value.Reproduced by the new test against the pre-fix code: a row entering with
Count=100, EstimatedSavings=600left asCount=10, EstimatedSavings=600, a 10x overstatement for that row.The figure flows into the run summary, the
ConfirmPurchaseprompt, the purchase report and the CSV, so an operator saw a capped run promising savings it cannot deliver. On a money path that is the wrong direction to be wrong in. Affects both the default and the--input-csvpath, and is pre-existing rather than introduced by #1825.The enumeration
The issue asked for every count-derived field to be enumerated before patching any one of them, since a report that is internally inconsistent is harder to notice than one uniformly wrong. The full
Recommendationstruct:Rescaled (extensive, whole-row totals):
EstimatedSavingsCommitmentCostOnDemandCostRecurringMonthlyCost*float64; nil stays nil)SavingsPlanDetails.HourlyCommitmentDeliberately not rescaled:
SavingsPercentage,BreakEvenMonthsRecommendedCountAverageInstancesUsedPerHour,UsageHistoryExistingCoveragePct,ExistingCoverageKnownRawRecommendationUpfrontCostandTotalCost, named as candidates in the issue, are fields ofOfferingDetails, a sibling struct that is not embedded inRecommendationand is not reachable from this path. No change needed.Two count-linear non-money fields are left alone and filed separately rather than silently ignored:
ProjectedCoverage/ProjectedUtilizationandDataWarehouseDetails.NumberOfNodes(#1845). Both are documented as out of scope on the helper.How
Truncated rows are scaled by the discrete count ratio through
common.ScaleRecommendationCosts, the helperApplyCoverage,ApplyTargetCoverageand family-NU sizing already used.ApplyInstanceLimitwas the one sizing path that mutatedCountwithout it.ScaleRecommendationCostsnow also scalesSavingsPlanDetails.HourlyCommitment. That line was duplicated at both of its existing call sites and missing at this new third one, which is precisely how the omission happened. An SP commitment is dollar-denominated, andApplyCountOverridesetsCounton SP recs without discriminating by commitment type, so an SP can reach the cap at a truncatable count; scaling its costs while leaving its commitment whole would produce an internally inconsistent row. The two existing call sites now delegate, which is provably equivalent (both previously overwroteDetailswith their own scaled copy after calling the helper, so the commitment is scaled exactly once either way).rec.Count > remainingandremaining >= 1together implyrec.Count >= 2, so the denominator is always positive and a non-positiveCountcan never enter the branch.Interaction with the #1825 ranking key
savingsPerInstancedividesEstimatedSavingsbyCount. Scaling both by the same ratio leaves the quotient exactly unchanged, so ranking behaviour is unaffected and the ordering still happens before the cap regardless.The comment on
sortBySavingsPerInstancecited #1830 as its justification ("a post-cap row's rate is inflated by exactly the amount the cap removed"). That reason evaporates with this fix, so it is corrected: the sort must still run first because the cap's selection consumes slice order, which has nothing to do with #1830.Existing compensation
Searched for anything that compensates for the un-rescaled value and would now double-correct. Nothing does.
sumPassedRecs,reporter.RenderSummary,calculateServiceStatsand the CSV writer are all plain summations of the post-cap rows, so they are silently wrong today and become correct with no change. The only reference to the bug was the stale comment above.One pre-existing test assertion (
TestCSVCapKeepsHighestSavingsNotFileOrder) hardcoded the un-rescaled100.00on a row truncated 6 to 4. That assertion encoded the bug and is updated to the invariant.Verification
Regression tests confirmed to fail against the pre-fix code, by assertion rather than panic:
Mutation-verified individually with
-run '^ExactName$' -count=1, every failure by assertion:LeavesUntruncatedRowsUntouched,TotalMatchesSumOfKeptRowsNonPositiveCountIsNotRescaled(observed+Inf/NaN)RecurringMonthlyCostto 0PreservesNilRecurringMonthlyCostHourlyCommitmentscalingBoth directions are covered: truncated rows are rescaled, and untruncated rows keep their money including pointer fields.
Suites:
cmd859 passed,pkg744 passed,providers/aws1212 passed (separate modules in thego.workmonorepo).gocyclo -over 10clean at the pre-commit hook's exact scope.golangci-lint v2.10.1(the CI-pinned version) reports 0 issues on the root module; thepkgmodule's 205 findings are identical toorigin/main, verified by diffing the normalized finding sets.Follow-ups filed
--override-counthas the identical defect on a neighbouring flag and runs upstream of the cap, so the cap's new rescale computes against an already-wrong base. Kept out of this PR to hold it to one concern.Closes #1830
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Bug Fixes
Documentation