Fix Issue 17518 - [Reg 2.063] confusing error message with inout constructor/ctor

[RazvanN7]

struct S
{
    this(inout Correct) inout
    {
    }
}

struct Correct {}
struct Wrong {}

S bug()
{
    return S(Wrong());
}

Yields: Error: inout method bug.S.this is not callable using a mutable object, because the modifier is checked first althoug the error comes from the fact the type is different. The fix is to see if any supplemental errors exists (which is used only for parameter types); if that is the case, then print the new more relevant error, otherwise print the former error.

[dlang-bot]

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Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	17518	regression	[Reg 2.063] confusing error message with inout constructor/ctor

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• Regression or critical bug fixes should always target the stable branch. Learn more about rebasing to stable or the D release process.

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Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub fetch digger
dub run digger -- build "master + dmd#9102"

[Geod24]

Why aren't overloaded functions covered ?

[RazvanN7]

@Geod24 Because when there are multiple overloads and none of them are matching, there is no specific overload to pinpoint the exact mistake.

[Geod24]

@RazvanN7 :

struct S
{
    this(inout Correct) inout
    {
    }
    this(int) {} // New addition
}

struct Correct {}
struct Wrong {}

S bug()
{
    return S(Wrong());
}

Results in:

msg.d(14): Error: none of the overloads of __ctor are callable using a mutable object, candidates are:
msg.d(3):        msg.S.this(inout(Correct) _param_0)
msg.d(6):        msg.S.this(int _param_0)

Which is obviously wrong. Using an error message similar to the one you put there ("is not callable using argument type...") makes more sense.