Make font template data load fallible

[jdm]

Remove a TODO around dealing with a failed file operation.

Can we write an automated test for this? I don't really know what font template data is, but this failure seems to be fontconfig-specific...

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• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #12037
• There are tests for these changes OR
• These changes do not require tests because _____

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This change is

[highfive]

Warning

• These commits modify gfx code, but no tests are modified. Please consider adding a test!

[cbrewster]

Reviewed 4 of 4 files at r1.
Review status: all files reviewed at latest revision, 2 unresolved discussions.

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components/gfx/font_template.rs, line 157 [r1] (raw file):

                                       .expect("Instantiation successful but no descriptor?")
                                       .distance_from(requested_descriptor);
                    (self.data().ok().map(|data| (data, distance)))

Remove extra parenthesis.

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components/gfx/platform/freetype/font_template.rs, line 6 [r1] (raw file):

use std::fs::File;
use std::io::{Read, Error};

Any reason why Error isn't imported as IoError here?

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Comments from Reviewable

[jdm]

Review status: all files reviewed at latest revision, 2 unresolved discussions.

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components/gfx/platform/freetype/font_template.rs, line 6 [r1] (raw file):

Previously, ConnorGBrewster (Connor Brewster) wrote…

Any reason why Error isn't imported as IoError here?

There's no conflicting Error already imported.

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Comments from Reviewable

[jdm]

@pcwalton Any idea what would be required in order to test this?

[jdm]

No idea about test stuff, but this is gathering dust. Let's review!

[pcwalton]

I don't know how testable this is. I think the error path only happens when the OS reports a font as installed but we couldn't open it for whatever reason, right?

[jdm]

Sounds plausible.

[pcwalton]

The only way I could think of to test this would be to either artificially simulate I/O errors or to do something silly like have the test harness set permissions on fonts to make them temporarily unreadable.

[jdm]

@bors-servo: r=pcwalton

[bors-servo]

📌 Commit fb943ab has been approved by pcwalton

[bors-servo]

⌛ Testing commit fb943ab with merge df09bb9...

[bors-servo]

💔 Test failed - mac-rel-wpt

[jdm]

@bors-servo: retry

• #11618

[bors-servo]

⌛ Testing commit fb943ab with merge a82d510...

[bors-servo]

☀️ Test successful - arm32, arm64, linux-dev, linux-rel, mac-dev-unit, mac-rel-css, mac-rel-wpt, windows-dev