Make profile-conversion snapshots more compact and meaningful by mstange · Pull Request #6152 · firefox-devtools/profiler

mstange · 2026-07-07T19:43:59Z

profile-conversion.test.ts was creating a snapshot file that was just a bunch of raw profile JSONs, with around 900 000 lines total.

There's no way to catch regressions with such a test. Whenever we change the shape of the tables in the profile format, it affects so many lines that github's diff viewer will not render the diff, and you wouldn't be able to meaningfully read it anyway.

For example, when I introduced the shared tables, I regressed the dhat importer (it was overwriting some tables with empty tables), and I missed the regression even though the test in theory "caught" it.

This commit replaces the raw profile snapshots with profile "summary" snapshots. See the new snapshot file for examples. I think the new snapshots are definitely more readable / reviewable, but there's also quite a bit of new code to generate them. I'd be happy to cut back on the amount of detail we collect when we make these summaries, to simplify that new code.
(Or maybe we can find a way to share some code with profiler-cli? Not sure.)

The new snapshot file is around 500 lines, and around 160 times smaller than the old snapshot file.

As a second measure of defense, this commit also adds a generic profile consistency checker function called assertProfileIntegrity. This would have caught the dhat regression by itself, because nativeAllocations.stack[0] = 55 would have tripped over the stack table being empty.

codecov · 2026-07-07T19:46:54Z

Codecov Report

❌ Patch coverage is 85.80645% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.53%. Comparing base (625c2f6) to head (b33aa23).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/test/fixtures/profile-summary.ts	85.80%	22 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6152      +/-   ##
==========================================
+ Coverage   83.50%   83.53%   +0.02%     
==========================================
  Files         342      343       +1     
  Lines       36522    36776     +254     
  Branches    10125    10321     +196     
==========================================
+ Hits        30497    30720     +223     
- Misses       5597     5629      +32     
+ Partials      428      427       -1

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canova

Nice! I like the new assertProfileIntegrity! Also being able to see the full stacks etc. will make it easier to catch stuff.

canova · 2026-07-10T10:05:55Z

+type ThreadSummary = {
+  name: string;
+  pid: string | number;
+  tid: string | number;
+  isMainThread: boolean;
+  sampleCount: number;
+  sampleWeightTotal: number | null;
+  markerCount: number;
+  markerNamesTop: string[];
+  jsAllocationCount: number;
+  nativeAllocationCount: number;
+  nativeAllocationWeightTotal: number | null;
+  weightType: string;
+};
+
+export type ProfileSummary = {
+  meta: {
+    product: string;
+    importedFrom: string | undefined;
+    interval: number;
+    version: number;
+    preprocessedProfileVersion: number;
+    symbolicated: boolean | undefined;
+    categoryNames: string[];
+    markerSchemaNames: string[];
+  };
+  sharedCounts: {
+    funcs: number;
+    frames: number;
+    stacks: number;
+    resources: number;
+    nativeSymbols: number;
+    strings: number;
+    libs: number;
+  };
+  threads: ThreadSummary[];
+};


Ah yeah, they kinda look like the summaries that we have in the profiler-cli. But I think it makes sense to keep them split. For example, I don't think sharedCounts makes sense for the cli.

canova · 2026-07-10T10:10:34Z

+        "nativeAllocationCount": 0,
+        "nativeAllocationWeightTotal": null,
+        "pid": "7567",
+        "sampleCount": 5,


It looks like for some cases these stacks can get pretty long in a line. I don't have an idea to improve it though. I think that's still an improvement over the ones that we had before, especially since we couldn't see the stacks easily.

Yeah. We can change it once it becomes a problem.

canova · 2026-07-10T10:12:13Z

+        );
+      }
+      const cat = markers.category[i];
+      if (cat < 0 || cat >= numCategories) {


I think we should also check for null/undefined here?

I went ahead and added checks for Number.isInteger everywhere.

profile-conversion.test.ts was creating a snapshot file that was just a bunch of raw profile JSONs, with around 900 000 lines total. There's no way to catch regressions with such a test. Whenever we change the shape of the tables in the profile format, it affects so many lines that github's diff viewer will not render the diff, and you wouldn't be able to meaningfully read it anyway. For example, when I introduced the shared tables, I regressed the dhat importer (it was overwriting some tables with empty tables), and I missed the regression even though the test in theory "caught" it. This commit replaces the raw profile snapshots with profile "summary" snapshots. See the new snapshot file for examples. I think the new snapshots are definitely more readable / reviewable, but there's also quite a bit of new code to generate them. I'd be happy to cut back on the amount of detail we collect when we make these summaries, to simplify that new code. (Or maybe we can find a way to share some code with profiler-cli? Not sure.) The new snapshot file is around 500 lines, and around 160 times smaller than the old snapshot file. As a second measure of defense, this commit also adds a generic profile consistency checker function called `assertProfileIntegrity`. This would have caught the dhat regression by itself, because nativeAllocations.stack[0] = 55 would have tripped over the stack table being empty.

Changes: [Sky Ning] Skip preview links for non-main PRs (#6161) [spokodev] fix(gecko-upgrade): don't crash on a counter with empty sample_groups (#6160) [fatadel] Show counter values over time in profiler-cli (#6136) [Markus Stange] Make profile-conversion snapshots more compact and meaningful (#6152) [Markus Stange] More typed arrays: sample + counter times, some frametable columns (#6139) [Nazım Can Altınova] Only render a marker url field as a link when the whole value is a URL (#6163) [fatadel] Show each counter's owning process in profiler-cli (#6164) [Nazım Can Altınova] Document the pre-existing thread info and network JSON schemas in the cli (#6171) [Markus Stange] Copy column contents in getRawSamplesTableBuilderFromExisting for consistency (#6168) [Markus Stange] Convert eligible columns to typed arrays when outputting from profiler-edit (#6167) [Markus Stange] Remove unused samples.thread column (#6151) [Markus Stange] Fixed botched merge which broke 'yarn ts' (#6174) [Nazım Can Altınova] Add marker handles to `profiler-cli thread network` (#6172) [Markus Stange] Update json-slabs 0.3.0 → 0.4.0 (major) (#6176) [Nazım Can Altınova] Surface network activity across profiler-cli (#6175) [Nazım Can Altınova] Add `profile meta` command to profiler-cli (#6177) [Markus Stange] Allow raw marker table's `startTime` and `endTime` columns to be Float64Array (#6169) [nightcityblade] Fix light theme text selection colors (#6186) [Nazım Can Altınova] Import source map URLs from Chrome DevTools traces (#6190) [Nazım Can Altınova] Rename yarn `build-profiler-cli` script to `build-cli` (#6191) [Nazım Can Altınova] Migrate husky to version 9 (#6201) [Nazım Can Altınova] Fix horizontal overflow when the transform navigator is long (#6199) [fatadel] Add a 'hexadecimal' marker schema field format (#6197) [Nazım Can Altınova] Bump source-map to 0.8.0 and remove the old type workaround (#6202) [Nazım Can Altınova] 🔃 Sync: l10n -> main (July 21, 2026) (#6209) And special thanks to our localizers: fr: parmegiani.thomas fr: Théo Chevalier sr: Марко Костић (Marko Kostić) sv-SE: Luna Jernberg tr: Grk zh-CN: Ariel zh-CN: Olvcpr423

mstange requested a review from canova July 7, 2026 19:43

mstange force-pushed the push-lzsvmxpoywyu branch 2 times, most recently from a0cb4dc to fd7d04a Compare July 7, 2026 19:59

canova approved these changes Jul 10, 2026

View reviewed changes

mstange added 2 commits July 10, 2026 15:15

Remove src/test/unit/__snapshots__/profile-conversion.test.ts.snap.

a692864

mstange force-pushed the push-lzsvmxpoywyu branch from fd7d04a to b33aa23 Compare July 10, 2026 21:10

mstange enabled auto-merge July 10, 2026 21:11

mstange merged commit 5fe8339 into firefox-devtools:main Jul 10, 2026
21 checks passed

canova mentioned this pull request Jul 21, 2026

Deploy July 21, 2026 #6210

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Make profile-conversion snapshots more compact and meaningful - #6152

Make profile-conversion snapshots more compact and meaningful#6152
mstange merged 2 commits into
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