Change Details

**Steps to replicate the issue** - Go to a test/sandbox wiki. - Create a redirect from [[Bar]] to [[Qux]]. - Create a redirect from [[Foo]] to [[Bar]]. Ignore any errors. - Go to https://nameofwiki/wiki/Foo. **What happens?** MediaWiki follows the first redirect, from [[Foo]] to [[Bar]], but then stops because [[Bar]] is also a redirect. - No error is thrown — the user is left to figure out what went wrong. - The user may want to fix the double redirect if their wiki has no bots performing this task. This requires them to return to Foo with `&redirect=no`, usually via the “redirected from” message, manually edit the page, and replace the target. **What should happen?** The problematic page is not [[Bar]], which functions normally, but [[Foo]]. It makes little sense to throw an error on [[Bar]]. Therefore, an error should be thrown on [[Foo]]. The message can look something like those you get if you try to create a double redirect: > ⚠️ This page is a double redirect to `{{{1}}}`, which redirects to `{{{2}}}`. For technical reasons, it does not function. Consider replacing this page's redirect target with `{{{2}}}`. However, for the user to actually see that error, the redirection needs to stop on [[Foo]], not [[Bar]] as it does now. To achieve that, the redirector needs to first check if its target is itself a redirect, and stop if that's the case. ** How to implement** [Need to edit the code that does the redirecting: where is the code that does this?] To check if the target is a redirect, MediaWiki needs to check `Title::isRedirect()` before following the redirect. ** Future possibilities** Stopping here makes it easier to implement a second step, where clicking a link provided by the error message, like: > https://en.wikipedia.org/w/index.php?title={{{1}}}&action=save&newredirtarget={{{2}}} would replace `{{{1}}}`'s redirect target with `{{{2}}}` if the user has the necessary permissions. Fixing this would also enable related things like throwing errors on broken redirects, and self-redirects {T396336}. **Impact** - MediaWiki has to stop somewhere; stopping on [[Foo]] is equally as inconvenient for the casual visitor as stopping on [[Bar]]. - The actual impact on Wikimedia Foundation wikis is minimal, since WMF wikis have bots to fix double redirects. This proposal mainly affects third-party wikis that lack such bots. - There may be some negative feedback due to the change from current behaviour because it’s “always been done this way,” but that's not a great reason for doing something — people will get used to this system fairly quickly. **Programming principles** This aligns with key programming and software design principles: - **Clarity and precision:** Errors should be reported as close as possible to their cause, making it clear where the problem originates. This simplifies debugging and reduces user confusion. - **Single Source of Truth (SSOT):** The problematic redirect resides in [[Foo]], which causes an invalid state by pointing to another redirect. Reporting the error on [[Foo]] preserves the principle that each error or piece of data should have a single authoritative source or location for truth. This reduces duplication of error handling and maintains system consistency. For more on SSOT, see [https://en.wikipedia.org/wiki/Single_source_of_truth](https://en.wikipedia.org/wiki/Single_source_of_truth). - **Fail fast and early:** Detecting and reacting to the problem immediately on the page causing it prevents cascading errors and harder-to-trace issues downstream. - **User experience:** Users expect that errors relate to the page they accessed. Reporting the error on [[Foo]] aligns with user expectations and facilitates appropriate corrective actions.

**Steps to replicate the issue** - Go to a test/sandbox wiki. - Create a redirect from [[Bar]] to [[Qux]]. - Create a redirect from [[Foo]] to [[Bar]]. Ignore any errors. - Go to https://nameofwiki/wiki/Foo. **What happens?** MediaWiki follows the first redirect, from [[Foo]] to [[Bar]], but then stops because [[Bar]] is also a redirect. - No error is thrown — the user is left to figure out what went wrong. - The user may want to fix the double redirect if their wiki has no bots performing this task. This requires them to return to Foo with `&redirect=no`, usually via the “redirected from” message, manually edit the page, and replace the target. **What should happen?** The problematic page is not [[Bar]], which functions without an issue, and where the wiki stops, but [[Foo]]. It makes little sense to throw an error on [[Bar]]. Therefore, an error should be thrown on [[Foo]]. The message can look something like those you get if you try to create a double redirect: > ⚠️ This page is a double redirect to `{{{1}}}`, which redirects to `{{{2}}}`. For technical reasons, it does not function. Consider replacing this page's redirect target with `{{{2}}}`. To generate and see that error, the redirection needs to stop on [[Foo]], not [[Bar]] as it does now. To achieve that, the redirector needs to first check if its target is itself a redirect, and stop if that's the case. If similar logic to that in redirectconstraint is followed, we can also deal here with redirect loops: (Foo->Bar->Foo). And we can also at this point check for target page (non)existence, and self-redirects, and show errors for them. ** How to implement** [Need to edit the code that does the redirecting: where is the code that does this?] To check if the target is a redirect, MediaWiki needs to check `Title::isRedirect()` before following the redirect. ** Future possibilities** Stopping here makes it easier to implement a second step, where clicking a link provided by the error message, like: > https://en.wikipedia.org/w/index.php?title={{{1}}}&action=save&newredirtarget={{{2}}} would replace `{{{1}}}`'s redirect target with `{{{2}}}` if the user has the necessary permissions. Fixing this would also enable related things like throwing errors on broken redirects, and self-redirects {T396336}. **Impact** - MediaWiki has to stop somewhere; stopping on [[Foo]] is equally as inconvenient for the casual visitor as stopping on [[Bar]]. - The actual impact on Wikimedia Foundation wikis is minimal, since WMF wikis have bots to fix double redirects. This proposal mainly affects third-party wikis that lack such bots. - There may be some negative feedback due to the change from current behaviour because it’s “always been done this way,” but that's not a great reason for doing something — people will get used to this system fairly quickly. **Programming principles** This aligns with key programming and software design principles: - **Clarity and precision:** Errors should be reported as close as possible to their cause, making it clear where the problem originates. This simplifies debugging and reduces user confusion. - **Single Source of Truth (SSOT):** The problematic redirect resides in [[Foo]], which causes an invalid state by pointing to another redirect. Reporting the error on [[Foo]] preserves the principle that each error or piece of data should have a single authoritative source or location for truth. This reduces duplication of error handling and maintains system consistency. For more on SSOT, see [https://en.wikipedia.org/wiki/Single_source_of_truth](https://en.wikipedia.org/wiki/Single_source_of_truth). - **Fail fast and early:** Detecting and reacting to the problem immediately on the page causing it prevents cascading errors and harder-to-trace issues downstream. - **User experience:** Users expect that errors relate to the page they accessed. Reporting the error on [[Foo]] aligns with user expectations and facilitates appropriate corrective actions. This is very similar to the logic needed for the RedirectConstraint.

**Steps to replicate the issue** - Go to a test/sandbox wiki. - Create a redirect from [[Bar]] to [[Qux]]. - Create a redirect from [[Foo]] to [[Bar]]. Ignore any errors. - Go to https://nameofwiki/wiki/Foo. **What happens?** MediaWiki follows the first redirect, from [[Foo]] to [[Bar]], but then stops because [[Bar]] is also a redirect. - No error is thrown — the user is left to figure out what went wrong. - The user may want to fix the double redirect if their wiki has no bots performing this task. This requires them to return to Foo with `&redirect=no`, usually via the “redirected from” message, manually edit the page, and replace the target. **What should happen?** The problematic page is not [[Bar]], which functions normallywithout an issue, and where the wiki stops, but [[Foo]]. It makes little sense to throw an error on [[Bar]]. Therefore, an error should be thrown on [[Foo]]. The message can look something like those you get if you try to create a double redirect: > ⚠️ This page is a double redirect to `{{{1}}}`, which redirects to `{{{2}}}`. For technical reasons, it does not function. Consider replacing this page's redirect target with `{{{2}}}`. However, for the user to actuallyTo generate and see that error, the redirection needs to stop on [[Foo]], not [[Bar]] as it does now. To achieve that, the redirector needs to first check if its target is itself a redirect, and stop if that's the case. If similar logic to that in redirectconstraint is followed, we can also deal here with redirect loops: (Foo->Bar->Foo). And we can also at this point check for target page (non)existence, and self-redirects, and stop if that's the casehow errors for them. ** How to implement** [Need to edit the code that does the redirecting: where is the code that does this?] To check if the target is a redirect, MediaWiki needs to check `Title::isRedirect()` before following the redirect. ** Future possibilities** Stopping here makes it easier to implement a second step, where clicking a link provided by the error message, like: > https://en.wikipedia.org/w/index.php?title={{{1}}}&action=save&newredirtarget={{{2}}} would replace `{{{1}}}`'s redirect target with `{{{2}}}` if the user has the necessary permissions. Fixing this would also enable related things like throwing errors on broken redirects, and self-redirects {T396336}. **Impact** - MediaWiki has to stop somewhere; stopping on [[Foo]] is equally as inconvenient for the casual visitor as stopping on [[Bar]]. - The actual impact on Wikimedia Foundation wikis is minimal, since WMF wikis have bots to fix double redirects. This proposal mainly affects third-party wikis that lack such bots. - There may be some negative feedback due to the change from current behaviour because it’s “always been done this way,” but that's not a great reason for doing something — people will get used to this system fairly quickly. **Programming principles** This aligns with key programming and software design principles: - **Clarity and precision:** Errors should be reported as close as possible to their cause, making it clear where the problem originates. This simplifies debugging and reduces user confusion. - **Single Source of Truth (SSOT):** The problematic redirect resides in [[Foo]], which causes an invalid state by pointing to another redirect. Reporting the error on [[Foo]] preserves the principle that each error or piece of data should have a single authoritative source or location for truth. This reduces duplication of error handling and maintains system consistency. For more on SSOT, see [https://en.wikipedia.org/wiki/Single_source_of_truth](https://en.wikipedia.org/wiki/Single_source_of_truth). - **Fail fast and early:** Detecting and reacting to the problem immediately on the page causing it prevents cascading errors and harder-to-trace issues downstream. - **User experience:** Users expect that errors relate to the page they accessed. Reporting the error on [[Foo]] aligns with user expectations and facilitates appropriate corrective actions. This is very similar to the logic needed for the RedirectConstraint.