recursive-patterns(18): Permit a constant pattern to be used with an open type as input #25995

gafter · 2018-04-06T17:28:45Z

Fixes #24550
Fixes dotnet/csharplang#1284
Also includes a slight code improvement for these and related cases.

@cston @agocke Please review
@dotnet/roslyn-compiler Additional reviews welcome

Fixes dotnet#24550 Fixes dotnet/csharplang#1284

alrz · 2018-04-06T18:38:38Z

for a moment I thought this is about dotnet/csharplang#356, is there anything planned to support it? #Resolved

gafter · 2018-04-06T20:26:41Z

We don't have any current plans around dotnet/csharplang#356, #Resolved

cston · 2018-04-10T22:42:56Z

src/Compilers/CSharp/Test/Emit/CodeGen/PatternTests.cs

+  IL_0015:  call       ""bool string.op_Equality(string, string)""
+  IL_001a:  ret
+  IL_001b:  ldc.i4.0
+  IL_001c:  ret
 }");
        }


} [](start = 8, length = 1)

Consider testing with nested value type:

class C<T> { internal struct S { } static bool Test(C<T>.S s) { return s == null; } } ``` #Resolved

Yes, need to adjust an assertion. Thanks!

In reply to: 180588905 [](ancestors = 180588905)

agocke · 2018-04-10T23:13:52Z

src/Compilers/CSharp/Test/Emit/CodeGen/PatternTests.cs

+  // Code size       10 (0xa)
+  .maxstack  2
+  IL_0000:  ldarg.0
+  IL_0001:  box        ""T""


Why do we need a box? It looks like this is generated because we choose object as the type of the pattern expression. Is there a way to avoid boxing? #Resolved

As far as I know, no. The CLR does not actually produce code for the box. If it is a reference type, the box goes away. If it is a value type, the whole method turns into false.

In reply to: 180594436 [](ancestors = 180594436)

Also change to using `out` patemters where apropos.

gafter · 2018-04-11T04:37:16Z

I've changed the implementation to give an error on e is null when e is a non-nullable value type. #Resolved

cston · 2018-04-11T04:51:04Z

src/Compilers/CSharp/Test/Emit/CodeGen/PatternTests.cs

+    internal struct S { }
+    static bool Test(S s)
+    {
+        return s is 1;


return s is 1 [](start = 8, length = 13)

Should this result in an "expr is always false" warning? #ByDesign

The short answer is no.

First, such warnings are implemented on another branch, but in any case only are given when the input is constant. This would be an error if it were determined that it can never match, but there are no rules that cause us to infer that. We used to depend on the absence of conversions, but that prevented matching a constant against a type parameter. The purpose of this change is specifically to remove the error that this cannot match.

In reply to: 180634901 [](ancestors = 180634901)

Added an open issue #26100 that would result in this case being an error. It is on the open LDM issue list for pattern-matching.

cston · 2018-04-11T05:11:04Z

src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs

+            // This permits us to match a value of type `IComparable<T>` with a pattern of type `int`.
+            if (inputType.ContainsTypeParameter() &&
+                // But do not permit matching null against a struct type.
+                (expression.ConstantValue != ConstantValue.Null || !inputType.IsNonNullableValueType()))


If inputType is known at compile-time not to be convertible to the expression type, are we reporting an error? #Resolved

Not if the input type is an open type. We need to be able to match an expression of type IComparable<T> to 3 even though there is no conversion between them. That change is the purpose of this PR.

In reply to: 180636955 [](ancestors = 180636955)

Ideally we should generate a warning for cases such as new C<T>() is 3. Please add a test.

In reply to: 180840789 [](ancestors = 180840789,180636955)

Done in a new iteration.

In reply to: 180844755 [](ancestors = 180844755,180840789,180636955)

agocke

LGTM

…et/roslyn into rpatterns18

Fixes dotnet#26098

cston · 2018-04-11T20:37:39Z

src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs

-                // But do not permit matching null against a struct type.
-                (expression.ConstantValue != ConstantValue.Null || !inputType.IsNonNullableValueType()))
+            bool inputContainsTypeParameter = inputType.ContainsTypeParameter();
+            HashSet<DiagnosticInfo> useSiteDiagnostics = null;


useSiteDiagnostics declaration can be moved inside if. #Resolved

cston · 2018-04-11T20:39:38Z

src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs

-                (expression.ConstantValue != ConstantValue.Null || !inputType.IsNonNullableValueType()))
+            bool inputContainsTypeParameter = inputType.ContainsTypeParameter();
+            HashSet<DiagnosticInfo> useSiteDiagnostics = null;
+            if (inputContainsTypeParameter)


We should report the same warning for non-generic cases such as new C() is 3?
#Resolved

That is accomplished by the call to ExpressionOfTypeMatchesPatternType below, and there is a test for it.

In reply to: 180890835 [](ancestors = 180890835)

gafter · 2018-04-11T22:25:32Z

@cston I believe I have addressed all of your comments. Do you have any more comments?

cston · 2018-04-11T23:05:40Z

src/Compilers/CSharp/Portable/Binder/Binder_Patterns.cs

+                    if (inputType.IsNullableType() && (convertedExpression.ConstantValue == null || !convertedExpression.ConstantValue.IsNull))
+                    {
+                        // Null is a special case here because we want to compare null to the Nullable<T> itself, not to the underlying type.
+                        var discardedDiagnostics = DiagnosticBag.GetInstance(); // We are not intested in the diagnostic that get created here


Typo: interested

…et/roslyn into rpatterns18

Permit a constant pattern to be used with an open type as input

a7c5425

Fixes dotnet#24550 Fixes dotnet/csharplang#1284

gafter added Area-Compilers New Language Feature - Pattern Matching Pattern Matching labels Apr 6, 2018

gafter added this to the 16.0 milestone Apr 6, 2018

gafter self-assigned this Apr 6, 2018

gafter requested review from agocke and cston April 6, 2018 17:28

gafter requested a review from a team as a code owner April 6, 2018 17:28

gafter added this to In Review in Compiler: Pattern-Matching Apr 6, 2018

gafter added the 4 - In Review A fix for the issue is submitted for review. label Apr 8, 2018

cston reviewed Apr 10, 2018

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agocke reviewed Apr 10, 2018

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gafter added 2 commits April 10, 2018 17:49

Adjust an assertion to account for our relaxed treatment of open types.

4bdce84

Forbid matching a struct type against null.

a1daa33

Also change to using `out` patemters where apropos.

cston reviewed Apr 11, 2018

View reviewed changes

agocke approved these changes Apr 11, 2018

View reviewed changes

gafter added 2 commits April 11, 2018 10:40

Merge branch 'features/recursive-patterns' of https://github.com/dotn…

4ce5edd

…et/roslyn into rpatterns18

Add handling for open class type vs value type constant pattern

c6b91e1

Fixes dotnet#26098

cston reviewed Apr 11, 2018

View reviewed changes

Move a declaration closer to its point of use.

9efbe9f

cston reviewed Apr 11, 2018

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cston approved these changes Apr 11, 2018

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Merge branch 'features/recursive-patterns' of https://github.com/dotn…

73f6b0d

…et/roslyn into rpatterns18

gafter merged commit b3a04b8 into dotnet:features/recursive-patterns Apr 12, 2018

gafter removed the 4 - In Review A fix for the issue is submitted for review. label Apr 12, 2018

gafter removed this from In Review in Compiler: Pattern-Matching Apr 12, 2018

MaStr11 mentioned this pull request Oct 3, 2018

IDE0041 Null check can be simplified is shown for Reference Equals of all generic parameters #23581

Closed

gafter mentioned this pull request Apr 2, 2019

t is null with LangVersion 7 should produce a diagnostic #34678

Closed

yyjdelete mentioned this pull request Apr 17, 2019

Crashes with NullReferenceException at Microsoft.CodeAnalysis.CSharp.ConversionsBase.ClassifyImplicitBuiltInConversionSlow #34980

Closed

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recursive-patterns(18): Permit a constant pattern to be used with an open type as input #25995

recursive-patterns(18): Permit a constant pattern to be used with an open type as input #25995

gafter commented Apr 6, 2018

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recursive-patterns(18): Permit a constant pattern to be used with an open type as input #25995

recursive-patterns(18): Permit a constant pattern to be used with an open type as input #25995

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gafter commented Apr 6, 2018

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