fix: skip unwanted stackframe on custom errors for faulty browsers #3555

leomelki · 2025-05-22T12:44:35Z

Motivation

Custom error stacktrace fix
Some browsers (safari/firefox) add the error constructor as a frame in the stacktrace.
In order to normalize the stacktrace, we need to remove it.

Changes

core/src/tools/stackTrace/computeStackTrace.ts was changed :

Added a detection of faulty browsers (relying on the runtime behaviour and not in heuristics not an empirical list of browser versions)
Added a detection of custom errors verifying if the error's constructor is a class (the behaviour difference only affects classes and not other objects)

test/e2e/scenario/rum/errors.scenario.ts was changed:

added 2 e2e tests to check for the fixed behaviour on custom errors with and without custom names.

Test instructions

Trigger a custom error in Chrome and in Firefox. They should now have the same stacktrace :

class CustomError extends Error {
  constructor(message) {
    super(message)
    this.name = 'CustomError'
  }
}
throw new CustomError('Custom error')

Tests done in staging

Checklist

Tested locally
Tested on staging
Added unit tests for this change.
Added e2e/integration tests for this change.

codecov-commenter · 2025-05-22T12:48:05Z

Codecov Report

Attention: Patch coverage is 62.50000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 92.01%. Comparing base (61824b8) to head (204bef7).
Report is 51 commits behind head on main.

Files with missing lines	Patch %	Lines
...ges/core/src/tools/stackTrace/computeStackTrace.ts	62.50%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3555      +/-   ##
==========================================
- Coverage   92.11%   92.01%   -0.11%     
==========================================
  Files         317      317              
  Lines        8082     8105      +23     
  Branches     1827     1835       +8     
==========================================
+ Hits         7445     7458      +13     
- Misses        637      647      +10

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leomelki · 2025-05-26T09:21:20Z

/to-staging

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child workflow execution error (type: devflow.Devflow_ToStaging, workflowID: 87ebd210-b208-4357-9819-e53bf0ea4fd0_35, runID: ece73205-7a71-49a0-86a8-44bd9d269bf2, initiatedEventID: 35, startedEventID: 36): child workflow execution error (type: devflow.Devflow_IntegratePullRequest, workflowID: ece73205-7a71-49a0-86a8-44bd9d269bf2_16, runID: 3d6b6caa-7bf7-474e-b305-2f7133bc0062, initiatedEventID: 16, startedEventID: 17): child workflow execution error (type: devflow.Devflow_Integrate, workflowID: 3d6b6caa-7bf7-474e-b305-2f7133bc0062_23, runID: 748a0383-fe00-4c56-bf51-a9ba4f6e739f, initiatedEventID: 23, startedEventID: 24): failed to update GIT_BASE_BRANCH: activity error (type: github.GithubService_GetFile, scheduledEventID: 31, startedEventID: 32, identity: 1@github-worker-8c57d5bd9-ql2c7@): GET https://api.github.com/repos/DataDog/browser-sdk/contents/.gitlab-ci.yml?ref=6f9271f5a31cd3bcc4ddfa8b2a5755fa2cf336fe: 504 We couldn't respond to your request in time. Sorry about that. Please try resubmitting your request and contact us if the problem persists. [] (type: ErrorResponse, retryable: true) (type: wrapError, retryable: true): activity error (type: github.GithubService_GetFile, scheduledEventID: 31, startedEventID: 32, identity: 1@github-worker-8c57d5bd9-ql2c7@): GET https://api.github.com/repos/DataDog/browser-sdk/contents/.gitlab-ci.yml?ref=6f9271f5a31cd3bcc4ddfa8b2a5755fa2cf336fe: 504 We couldn't respond to your request in time. Sorry about that. Please try resubmitting your request and contact us if the problem persists. [] (type: ErrorResponse, retryable: true)

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leomelki · 2025-05-26T09:23:00Z

/to-staging

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leomelki · 2025-05-26T11:45:31Z

/to-staging

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…s UNKNOWN_FUNCTION

skimi · 2025-05-27T12:50:25Z

packages/core/src/tools/stackTrace/computeStackTrace.ts

+let WRONGLY_REPORTING_CUSTOM_ERRORS: boolean | undefined
+
+function isWronglyReportingCustomErrors() {
+  if (WRONGLY_REPORTING_CUSTOM_ERRORS !== undefined) {
+    return WRONGLY_REPORTING_CUSTOM_ERRORS
+  }


Could we initialize this when the file loads and avoid the if (WRONGLY_REPORTING_CUSTOM_ERRORS !== undefined)?

And WRONGLY_REPORTING_CUSTOM_ERRORS could be used directly, skipping isWronglyReportingCustomErrors

Suggested change

let WRONGLY_REPORTING_CUSTOM_ERRORS: boolean | undefined

function isWronglyReportingCustomErrors() {

if (WRONGLY_REPORTING_CUSTOM_ERRORS !== undefined) {

return WRONGLY_REPORTING_CUSTOM_ERRORS

}

const WRONGLY_REPORTING_CUSTOM_ERRORS = (function isWronglyReportingCustomErrors() {

...

})();

I tried but the linter doesn't like it :

CallExpression can have side effects when the module is evaluated. Maybe move it in a function declaration?eslint(local-rules/disallow-side-effects)

I can change the code to do this outside of a function but it think it would be way less clean

packages/core/src/tools/stackTrace/computeStackTrace.spec.ts

BenoitZugmeyer · 2025-06-02T15:48:09Z

packages/core/src/tools/stackTrace/computeStackTrace.ts

+    }
+  }
+
+  const [customError, normalError] = [DatadogTestCustomError, Error].map((errConstructor) => new errConstructor()) // so that both errors should exactly have the same stacktrace


praise: smart!

BenoitZugmeyer · 2025-06-02T15:55:21Z

packages/core/src/tools/stackTrace/computeStackTrace.ts

@@ -48,6 +48,33 @@ export function computeStackTrace(ex: unknown): StackTrace {
    })
  }

+  if (stack.length > 0 && isWronglyReportingCustomErrors()) {
+    // if we are wrongly reporting custom errors
+    if (ex instanceof Error && isErrorCustomError(ex)) {


suggestion: the isErrorCustomError(ex) check should not be needed here
suggestion: merge the two if

done ✅ (with the iserrorcustomerror to isnonnativeclassprototype function change)

BenoitZugmeyer · 2025-06-02T16:14:21Z

packages/core/src/tools/stackTrace/computeStackTrace.ts

+      const constructors: string[] = []
+
+      // go through each inherited constructor
+      let cstr: object | undefined = ex
+      while ((cstr = Object.getPrototypeOf(cstr)) !== Error.prototype && cstr) {
+        const errorConstructorName = cstr.constructor?.name || UNKNOWN_FUNCTION
+        constructors.push(errorConstructorName)
+      }
+
+      // traverse the stacktrace in reverse order because the stacktrace starts with the last inherited constructor
+      // we check constructor names to ensure we remove the correct frame (and there isn't a weird unsupported environment behavior)
+      for (let i = constructors.length - 1; i >= 0; i--) {
+        if (stack[0]?.func === constructors[i]) {
+          // if the first stack frame is the custom error constructor
+          stack.shift() // remove it
+        } else {
+          break
+        }
+      }


suggestion:
Can we have something like this?

if (isWronglyReportingCustomErrors() && ex instanceof Error) { let currentPrototype = Object.getPrototypeOf(ex) while ( currentPrototype && isNonNativeClassPrototype(currentPrototype) && stack.length > 0 && stack[0].func === (currentPrototype.constructor.name || UNKNOWN_FUNCTION) ) { stack.shift() currentPrototype = Object.getPrototypeOf(currentPrototype) } }

with

function isNonNativeClassPrototype(prototype: object) { return String(prototype.constructor).startsWith('class ') }

moving the currentPrototype assignment in the while loop would increase the build size slightly as we would have to initialize the variable. Is this necessary ?

Ok, WDYT of:

if (isWronglyReportingCustomErrors() && ex instanceof Error) { let currentPrototype = ex while ( (currentPrototype = Object.getPrototypeOf(currentPrototype)) && isNonNativeClassPrototype(currentPrototype) && stack.length > 0 && stack[0].func === (currentPrototype.constructor.name || UNKNOWN_FUNCTION) ) { stack.shift() } }

It's a bit more cryptic but... I'd be fine with it.

packages/core/src/tools/stackTrace/computeStackTrace.ts

test/e2e/scenario/rum/errors.scenario.ts

packages/core/src/tools/stackTrace/computeStackTrace.ts

cit-pr-commenter · 2025-06-03T09:04:08Z

Bundles Sizes Evolution

📦 Bundle Name	Local Size	𝚫	𝚫%	Status
Rum	145.98 KiB	145.98 KiB	N/A%	✅
Rum Recorder	18.03 KiB	18.03 KiB	N/A%	✅
Rum Profiler	4.73 KiB	4.73 KiB	N/A%	✅
Logs	50.88 KiB	50.88 KiB	N/A%	✅
Rum Slim	105.62 KiB	105.62 KiB	N/A%	✅
Worker	23.59 KiB	23.59 KiB	N/A%	✅

🚀 CPU Performance

Action Name	Base Average Cpu Time (ms)	Local Average Cpu Time (ms)	𝚫
addglobalcontext	N/A	0.007	0.007
addaction	N/A	0.024	0.024
addtiming	N/A	0.005	0.005
adderror	N/A	0.024	0.024
startstopsessionreplayrecording	N/A	0.001	0.001
startview	N/A	0.005	0.005
logmessage	N/A	0.030	0.030

🧠 Memory Performance

Action Name	Base Consumption Memory (bytes)	Local Consumption Memory (bytes)	𝚫 (bytes)
addglobalcontext	NaN KiB	26.41 KiB	NaN KiB
addaction	NaN KiB	57.12 KiB	NaN KiB
addtiming	NaN KiB	24.69 KiB	NaN KiB
adderror	NaN KiB	60.23 KiB	NaN KiB
startstopsessionreplayrecording	NaN KiB	24.45 KiB	NaN KiB
startview	NaN KiB	430.62 KiB	NaN KiB
logmessage	NaN KiB	58.03 KiB	NaN KiB

🔗 RealWorld

leomelki · 2025-06-03T13:21:22Z

Just found an INSANE behaviour from WebKit (not Firefox) :

When a custom error class does not have a constructor defined, it is not shown in the parsed stacktrace.

Why ?

Because WebKit does not report its stackframe origin (line/file). Thus, the parsing fails.

…tructor on webkit

packages/core/src/tools/stackTrace/computeStackTrace.ts

test/e2e/scenario/rum/errors.scenario.ts

leomelki · 2025-06-06T15:14:37Z

@BenoitZugmeyer

Can you add a comment to clarify this?

Done in f6346fd ✅

leomelki added 5 commits May 22, 2025 12:00

add custom error detection + stack fix

c2d68d6

remove logs

474a94c

refactor:

bbb32ce

add test

42e7289

reset wrongly reporting custom errors flag in test

d2e6c28

leomelki added 4 commits May 22, 2025 15:12

format

1c1e4cf

fix lint

87f8390

refactor

4369bde

improve format

b4b96ff

dd-mergequeue bot added a commit that referenced this pull request May 26, 2025

Integrate leomelki/ERRORT-5209_custom-error-stacktrace-fix (#3555) in…

c5b4e16

…to staging-22 Integrated commit sha: b4b96ff Co-authored-by: leomelki <[email protected]>

dd-devflow bot added the staging-22 label May 26, 2025

not minify classnames starting with _

2c54f66

DataDog deleted a comment from dd-devflow bot May 26, 2025

fix format

b8edf0b

dd-mergequeue bot added a commit that referenced this pull request May 26, 2025

Integrate leomelki/ERRORT-5209_custom-error-stacktrace-fix (#3555) in…

cc692c8

…to staging-22 Integrated commit sha: b8edf0b Co-authored-by: leomelki <[email protected]>

leomelki marked this pull request as ready for review May 26, 2025 13:14

leomelki requested a review from a team as a code owner May 26, 2025 13:14

change logic - if the constructor don't have a name, it is reported a…

ced163c

…s UNKNOWN_FUNCTION

skimi reviewed May 27, 2025

View reviewed changes

packages/core/src/tools/stackTrace/computeStackTrace.spec.ts Outdated Show resolved Hide resolved

leomelki added 2 commits May 27, 2025 17:33

add e2e firefox test

c4e976a

fix format + fix test + add test for custom errors with custom name

26b319f

leomelki added 3 commits June 2, 2025 14:58

remove now useless and wrong comment

08a8952

add classless class in error inheritance reporting test

8b44297

rename test case

1e14089

BenoitZugmeyer reviewed Jun 2, 2025

View reviewed changes

leomelki added 6 commits June 3, 2025 10:42

remove useless constructors

cd2db47

move from isCustomError to isNonNativeClassPrototype

8cbb8a2

add unit test

32b67eb

remove useless check

f468091

refactor: rename prototype variable + removed useless check

f892405

format

e69ca43

leomelki added 3 commits June 3, 2025 11:05

removed duplicated test

3852988

add log in test

0db1e81

add test log

0c9fa14

add unit test for inheritance + fix for non native error without cons…

8bb813c

…tructor on webkit

leomelki force-pushed the leomelki/ERRORT-5209_custom-error-stacktrace-fix branch 3 times, most recently from dfd486b to 734d990 Compare June 3, 2025 14:16

fix gecko stackframe parsing regex

79239b7

leomelki force-pushed the leomelki/ERRORT-5209_custom-error-stacktrace-fix branch from 734d990 to 79239b7 Compare June 3, 2025 14:30

leomelki commented Jun 3, 2025

View reviewed changes

packages/core/src/tools/stackTrace/computeStackTrace.ts Show resolved Hide resolved

refactor: remove log in test

336aefd

BenoitZugmeyer reviewed Jun 6, 2025

View reviewed changes

packages/core/src/tools/stackTrace/computeStackTrace.ts Show resolved Hide resolved

packages/core/src/tools/stackTrace/computeStackTrace.ts Outdated Show resolved Hide resolved

test/e2e/scenario/rum/errors.scenario.ts Show resolved Hide resolved

leomelki added 3 commits June 6, 2025 17:06

add anonymous inheritance unit test

53218a7

refactor: merged isWronglyReportingCustomErrorsCache conditions

b38bc1c

refactor: add comment explaining the concept of anonymous class in test

f6346fd

leomelki added 2 commits June 10, 2025 11:58

test: add test for empty lines support

2f88472

move condition to for condition to shrink code

204bef7

fix: skip unwanted stackframe on custom errors for faulty browsers #3555

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fix: skip unwanted stackframe on custom errors for faulty browsers #3555

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