PSA: Undefined Grit variables will cause build errors moving forward

[Demetrios Papadopoulos]

Hi chromium-dev,

What's changing?

Previously, undefined Grit variables in <if expr="..."> statements would silently be treated as False (see code here)

After this CL lands, undefined variables will cause a build error instead (also see crbug.com/1316544).

Why?

The previous behavior is fragile and has been the source of several bugs over time. Example types of bugs that were previously not caught at build time:

• typos
• confusion of GN and Grit variables which don't always match, for example is_mac (GN) vs is_macosx (Grit)
• obsolete references to removed/renamed Grit variables

Example bugs that would have been caught at build time with the new checks: crbug.com/1317459, crbug.com/1319668, cl/3595220, cl/3600260

Example error (condensed)

[12492/32900] ACTION //chrome/browser:resources_grit(//build/toolchain/linux:clang_x64)
...
AssertionError: undefined Grit variable found: foo

As a follow-up, I plan to improve the error message to also mention the name of the file that contains the undefined variable, but that requires a bit of plumbing and I did not want to block the addition of the new check on it. The path to the failing target is already a good indication of where to look for the undefined variable.

I expect the new behavior to prevent <if expr>-related bugs from entering the codebase as well as save time that would previously be spent on debugging why a certain string/resource/piece-of-code is missing unexpectedly on a certain platform. Feel free to comment on the bug or here if you have any concerns or questions.

Thank you,

Demetrios

[David Dorwin]

Thank you for taking the initiative to fix this and all the cases that were blocking it!

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