Bug 22514 – Invalid duplicate case error when the switched value has errors

The following code causes invalid `duplicate case X` errors when compiled with dmd > 2.094: void main() { switch (doesNotExist) { case 1: break; case 2: break; case 3: break; } } Apparently introduced / revealed by https://github.com/dlang/dmd/pull/11467.

@MoonlightSentinel created dlang/dmd pull request #13309 "Fix 22514 - Don't raise invalid duplicate case errors when the switch..." fixing this issue: - Fix 22514 - Don't raise invalid duplicate case errors when the switch... ... has other errors. The duplicate case checks triggered because #11467 made `ErrorExp` into a singleton and hence caused `ErrorExp` == `ErrorExp` to yield true even if those errors were caused by different expressions. This situation can arise from two different user errors: 1. the case is faulty, e.g. an unknown variable 2. the switch'ed value is faulty, causing `implicitCastTo` to generate an `ErrorExp`. This commit fixes (1) by simply skipping the ducplicated case check for `ErrorExp` because it doesn't have enough information. (2) requires the case expression to not be coerced into the switched type s.t. we can at least detect some errors while also keeping the actual case expression to offer helpful diagnostics. https://github.com/dlang/dmd/pull/13309

check https://issues.dlang.org/show_bug.cgi?id=21389, it was likely the same

*** Issue 21389 has been marked as a duplicate of this issue. ***

@MoonlightSentinel created dlang/dmd pull request #13310 "[IGNORE] Check if other code relyies on invalid ErrorExp identity" fixing this issue: - Fix 22514 - Don't raise invalid duplicate case errors when the switch... ... has other errors. The duplicate case checks triggered because #11467 made `ErrorExp` into a singleton and hence caused `ErrorExp` == `ErrorExp` to yield true even if those errors were caused by different expressions. This situation can arise from two different user errors: 1. the case is faulty, e.g. an unknown variable 2. the switch'ed value is faulty, causing `implicitCastTo` to generate an `ErrorExp`. This commit fixes (1) by simply skipping the ducplicated case check for `ErrorExp` because it doesn't have enough information. (2) requires the case expression to not be coerced into the switched type s.t. we can at least detect some errors while also keeping the actual case expression to offer helpful diagnostics. https://github.com/dlang/dmd/pull/13310

dlang/dmd pull request #13309 "Fix 22514 - Don't raise invalid duplicate case errors when the switch..." was merged into stable: - dcdfb7959e2e1036fbbc7de10b2e663d80b80d3f by MoonlightSentinel: Fix 22514 - Don't raise invalid duplicate case errors when the switch... ... has other errors. The duplicate case checks triggered because #11467 made `ErrorExp` into a singleton and hence caused `ErrorExp` == `ErrorExp` to yield true even if those errors were caused by different expressions. This situation can arise from two different user errors: 1. the case is faulty, e.g. an unknown variable 2. the switch'ed value is faulty, causing `implicitCastTo` to generate an `ErrorExp`. This commit fixes (1) by simply skipping the ducplicated case check for `ErrorExp` because it doesn't have enough information. (2) requires the case expression to not be coerced into the switched type s.t. we can at least detect some errors while also keeping the actual case expression to offer helpful diagnostics. https://github.com/dlang/dmd/pull/13309

dlang/dmd pull request #13421 "merge stable" was merged into master: - d14ed1e9c2183a533b6f275be2c6692e9aad4e9e by MoonlightSentinel: Fix 22514 - Don't raise invalid duplicate case errors when the switch... ... has other errors. The duplicate case checks triggered because #11467 made `ErrorExp` into a singleton and hence caused `ErrorExp` == `ErrorExp` to yield true even if those errors were caused by different expressions. This situation can arise from two different user errors: 1. the case is faulty, e.g. an unknown variable 2. the switch'ed value is faulty, causing `implicitCastTo` to generate an `ErrorExp`. This commit fixes (1) by simply skipping the ducplicated case check for `ErrorExp` because it doesn't have enough information. (2) requires the case expression to not be coerced into the switched type s.t. we can at least detect some errors while also keeping the actual case expression to offer helpful diagnostics. https://github.com/dlang/dmd/pull/13421