Expose CSS specificity component breakdown via CDP [chromium/src : main]

[Helmut Januschka (Gerrit)]

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File-level comment, Patchset 2 (Latest):

Helmut Januschka . resolved

hi @pfa...@chromium.org since you are on the devtools part of this change, could you review it?

please let me know if you want me to address anything

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[Rune Lillesveen (Gerrit)]

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File third_party/blink/renderer/core/inspector/inspector_style_sheet.cc

Line 208, Patchset 2 (Latest): simple_selector->SimpleSelectorSpecificityTuple();

Rune Lillesveen . unresolved

This doesn't do a breakdown of nesting selectors? Any :is() would regarded a single unit?

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[Helmut Januschka (Gerrit)]

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File third_party/blink/renderer/core/inspector/inspector_style_sheet.cc

Line 208, Patchset 2: simple_selector->SimpleSelectorSpecificityTuple();

Rune Lillesveen . resolved

This doesn't do a breakdown of nesting selectors? Any :is() would regarded a single unit?

Helmut Januschka

Gosh yes, `:is()` showed up as a single component with the max argument specificity.

Refactored the component builder to recurse into specificity-bearing selector lists, and tested on the devtools cl

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[Philip Pfaffe (Gerrit)]

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Commit Message

Line 9, Patchset 3 (Latest):Compute per-simple-selector specificity contributions in Blink and attach them to CSS.Specificity so DevTools can render an accurate breakdown without parsing selectors client-side.

Philip Pfaffe . unresolved

What's the advantage of doing this in the backend if we have to compute the components manually?

File third_party/blink/renderer/core/css/css_selector.h

Line 185, Patchset 3 (Latest): // Returns specificity components for this single simple selector.

Philip Pfaffe . unresolved

Aren't these the same?

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[Helmut Januschka (Gerrit)]

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Commit Message

Line 9, Patchset 3 (Latest):Compute per-simple-selector specificity contributions in Blink and attach them to CSS.Specificity so DevTools can render an accurate breakdown without parsing selectors client-side.

Philip Pfaffe . unresolved

What's the advantage of doing this in the backend if we have to compute the components manually?

Helmut Januschka

Per your and Bramus's feedback on the DevTools CL (crrev.com/c/7645008, PS3), parsing selectors in the frontend was "fragile and not future friendly" thats why i did the CL.

File third_party/blink/renderer/core/css/css_selector.h

Line 185, Patchset 3 (Latest): // Returns specificity components for this single simple selector.

Philip Pfaffe . resolved

Aren't these the same?

Helmut Januschka

They are not, `SpecificityTuple()` walks `NextSimpleSelector()` and returns the aggregated total for the whole complex selector, while `SimpleSelectorSpecificityTuple()` only returns this one simple selector's contribution (via `SpecificityForOneSelector()`). DevTools needs the per-simple-selector breakdown to render the per-component tooltip.

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[Philip Pfaffe (Gerrit)]

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Commit Message

Line 9, Patchset 3 (Latest):Compute per-simple-selector specificity contributions in Blink and attach them to CSS.Specificity so DevTools can render an accurate breakdown without parsing selectors client-side.

Philip Pfaffe . unresolved

What's the advantage of doing this in the backend if we have to compute the components manually?

Helmut Januschka

Per your and Bramus's feedback on the DevTools CL (crrev.com/c/7645008, PS3), parsing selectors in the frontend was "fragile and not future friendly" thats why i did the CL.

Philip Pfaffe

True, I'm concernd with the manual work required. Any chance we can reuse the implementation from elsewhere? If we're recomputing the data in the inspector, we're not really improving fragility.

File third_party/blink/renderer/core/css/css_selector.h

Line 185, Patchset 3 (Latest): // Returns specificity components for this single simple selector.

Philip Pfaffe . resolved

Aren't these the same?

Helmut Januschka

They are not, `SpecificityTuple()` walks `NextSimpleSelector()` and returns the aggregated total for the whole complex selector, while `SimpleSelectorSpecificityTuple()` only returns this one simple selector's contribution (via `SpecificityForOneSelector()`). DevTools needs the per-simple-selector breakdown to render the per-component tooltip.

Philip Pfaffe

Ah, that's subtle, ack!

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[Helmut Januschka (Gerrit)]

Attention needed from Philip Pfaffe

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Commit Message

Line 9, Patchset 3:Compute per-simple-selector specificity contributions in Blink and attach them to CSS.Specificity so DevTools can render an accurate breakdown without parsing selectors client-side.

Philip Pfaffe . resolved

What's the advantage of doing this in the backend if we have to compute the components manually?

Helmut Januschka

Per your and Bramus's feedback on the DevTools CL (crrev.com/c/7645008, PS3), parsing selectors in the frontend was "fragile and not future friendly" thats why i did the CL.

Philip Pfaffe

True, I'm concernd with the manual work required. Any chance we can reuse the implementation from elsewhere? If we're recomputing the data in the inspector, we're not really improving fragility.

Helmut Januschka

PTAL current PS, think i found a way that does not duplicate code, and also not make the change to brutal!

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[Philip Pfaffe (Gerrit)]

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Commit Message

Line 9, Patchset 3:Compute per-simple-selector specificity contributions in Blink and attach them to CSS.Specificity so DevTools can render an accurate breakdown without parsing selectors client-side.

Philip Pfaffe . resolved

What's the advantage of doing this in the backend if we have to compute the components manually?

Helmut Januschka

Per your and Bramus's feedback on the DevTools CL (crrev.com/c/7645008, PS3), parsing selectors in the frontend was "fragile and not future friendly" thats why i did the CL.

Philip Pfaffe

True, I'm concernd with the manual work required. Any chance we can reuse the implementation from elsewhere? If we're recomputing the data in the inspector, we're not really improving fragility.

Helmut Januschka

PTAL current PS, think i found a way that does not duplicate code, and also not make the change to brutal!

Philip Pfaffe

much nicer, thanks!

File third_party/blink/renderer/core/inspector/inspector_style_sheet.cc

Line 198, Patchset 4 (Latest): current_compound.clear();

Philip Pfaffe . unresolved

This is my personal taste, but I find using a container after move risky (the code is correct currently, but future changes can easily introduce bugs). Can we write this with out use after moving?

Line 204, Patchset 4 (Latest): std::reverse(compounds.begin(), compounds.end());

Philip Pfaffe . unresolved

use base::Reversed instead

Line 209, Patchset 4 (Latest): for (const CSSSelector* simple_selector : compound) {

Philip Pfaffe . unresolved

do we also need to reverse compound?

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[Helmut Januschka (Gerrit)]

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File third_party/blink/renderer/core/inspector/inspector_style_sheet.cc

Line 198, Patchset 4: current_compound.clear();

Philip Pfaffe . resolved

This is my personal taste, but I find using a container after move risky (the code is correct currently, but future changes can easily introduce bugs). Can we write this with out use after moving?

Helmut Januschka

Done

Line 204, Patchset 4: std::reverse(compounds.begin(), compounds.end());

Philip Pfaffe . resolved

use base::Reversed instead

Helmut Januschka

Done

Line 209, Patchset 4: for (const CSSSelector* simple_selector : compound) {

Philip Pfaffe . resolved

do we also need to reverse compound?

Helmut Januschka

nice catch, yes!

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File third_party/blink/renderer/core/inspector/inspector_style_sheet.cc

Line 209, Patchset 4: for (const CSSSelector* simple_selector : compound) {

Philip Pfaffe . resolved

do we also need to reverse compound?

Helmut Januschka

nice catch, yes!

Helmut Januschka

ok reverted, this broke tests

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