Flamechart crash fix (#6336)

* Revert the previous fix that didn't work

* Type tags checks instead of instanceof checks

Author: manojVivek

ui/packages/shared/profile/src/ProfileFlameChart/index.tsx

@@ -22,7 +22,12 @@ import {TimeUnits, formatDate, formatDuration} from '@parca/utilities';
 
 import ProfileFlameGraph, {validateFlameChartQuery} from '../ProfileFlameGraph';
 import {boundsFromProfileSource} from '../ProfileFlameGraph/FlameGraphArrow/utils';
-import {MergedProfileSource, ProfileSource, timeFormat} from '../ProfileSource';
+import {
+  MergedProfileSource,
+  ProfileSource,
+  isMergedProfileSource,
+  timeFormat,
+} from '../ProfileSource';
 import {useProfileFilters} from '../ProfileView/components/ProfileFilters/useProfileFilters';
 import type {SamplesData} from '../ProfileView/types/visualization';
 import {flamechartDimensionParser} from '../hooks/urlParsers';
@@ -83,7 +88,7 @@ const createFilteredProfileSource = (
   profileSource: ProfileSource,
   selectedTimeframe: {labels: LabelSet; bounds: NumberDuo}
 ): ProfileSource | null => {
-  if (!(profileSource instanceof MergedProfileSource)) {
+  if (!isMergedProfileSource(profileSource)) {
     return null;
   }
 

ui/packages/shared/profile/src/ProfileFlameGraph/FlameGraphArrow/utils.ts

@@ -22,7 +22,7 @@ import {
 } from '@parca/store';
 import {divide, getLastItem, valueFormatter} from '@parca/utilities';
 
-import {MergedProfileSource, ProfileSource} from '../../ProfileSource';
+import {ProfileSource, isMergedProfileSource} from '../../ProfileSource';
 import {BigIntDuo, hexifyAddress} from '../../utils';
 import {
   FIELD_DEPTH,
@@ -115,7 +115,7 @@ export const boundsFromProfileSource = (profileSource?: ProfileSource): BigIntDu
     return [0n, 1n];
   }
 
-  if (!(profileSource instanceof MergedProfileSource)) {
+  if (!isMergedProfileSource(profileSource)) {
     return [0n, 1n];
   }
 

ui/packages/shared/profile/src/ProfileSource.tsx

@@ -120,7 +120,32 @@ export class MergedProfileSelection implements ProfileSelection {
   }
 }
 
+// Type tag carried on instances so we can identify them reliably even when the
+// class gets duplicated across bundle chunks (prod builds sometimes end up with
+// two copies of the same class, making `instanceof` unreliable).
+export const PROFILE_SOURCE_TYPE_MERGED = 'merged' as const;
+export const PROFILE_SOURCE_TYPE_DIFF = 'diff' as const;
+
+const getProfileSourceType = (source: ProfileSource | null | undefined): string | undefined => {
+  if (source == null) return undefined;
+  const tag = (source as {profileSourceType?: unknown}).profileSourceType;
+  return typeof tag === 'string' ? tag : undefined;
+};
+
+export const isMergedProfileSource = (
+  source: ProfileSource | null | undefined
+): source is MergedProfileSource => {
+  return getProfileSourceType(source) === PROFILE_SOURCE_TYPE_MERGED;
+};
+
+export const isProfileDiffSource = (
+  source: ProfileSource | null | undefined
+): source is ProfileDiffSource => {
+  return getProfileSourceType(source) === PROFILE_SOURCE_TYPE_DIFF;
+};
+
 export class ProfileDiffSource implements ProfileSource {
+  readonly profileSourceType = PROFILE_SOURCE_TYPE_DIFF;
   a: ProfileSource;
   b: ProfileSource;
   profileType: ProfileType;
@@ -194,6 +219,7 @@ function nanosToTimestamp(nanos: bigint): Timestamp {
 }
 
 export class MergedProfileSource implements ProfileSource {
+  readonly profileSourceType = PROFILE_SOURCE_TYPE_MERGED;
   mergeFrom: bigint;
   mergeTo: bigint;
   query: Query;

ui/packages/shared/utilities/src/bigint.ts

@@ -55,9 +55,8 @@ export const scaleLinear = (
     console.log('domainRange', domainRange, rangeRange, divide(rangeRange, domainRange));
   }
 
-  // guard 0n to avoid BigInt(Infinity).
-  const rate =
-    domainRange === 0n ? 0n : BigInt(Math.round(divide(rangeRange, domainRange) * MULTIPLE));
+  // rate * MULTIPLE to retain the decimal places in BigInt format, then divide by MULTIPLE to get the final result
+  const rate = BigInt(Math.round(divide(rangeRange, domainRange) * MULTIPLE));
 
   const func = (x: bigint): number => {
     if (debugLog) {
@@ -75,9 +74,6 @@ export const scaleLinear = (
   };
 
   func.ticks = (count = 5): bigint[] => {
-    if (count <= 1 || domainRange === 0n) {
-      return [domainMin];
-    }
     const step = domainRange / BigInt(count - 1);
     const ticks: bigint[] = [];
     for (let i = 0; i < count; i++) {