Fix: warn FS0049 on upper union case labels (#19003)

Author: edgarfgp

docs/release-notes/.FSharp.Compiler.Service/11.0.0.md

@@ -4,7 +4,8 @@
 * Fix excessive StackGuard thread jumping ([PR #18971](https://github.com/dotnet/fsharp/pull/18971))
 * Checking: Fix checking nested fields for records and anonymous ([PR #18964](https://github.com/dotnet/fsharp/pull/18964))
 * Fix name is bound multiple times is not reported in 'as' pattern ([PR #18984](https://github.com/dotnet/fsharp/pull/18984))
-* Type relations cache: handle potentially "infinite" types ([PR #19010](https://github.com/dotnet/fsharp/pull/19010))
+* Fix: warn FS0049 on upper union case label. ([PR #19003](https://github.com/dotnet/fsharp/pull/19003))
+* Type relations cache: handle potentially "infinite" types ([PR #19010](https://github.com/dotnet/fsharp/pull/19010))  
 
 ### Added
 

src/Compiler/Checking/CheckPatterns.fs

@@ -401,15 +401,18 @@ and TcPatNamedAs warnOnUpper cenv env valReprInfo vFlags patEnv ty synInnerPat i
     phase2, acc
 
 and TcPatUnnamedAs warnOnUpper cenv env vFlags patEnv ty pat1 pat2 m =
-    let pats = [pat1; pat2]
-    let warnOnUpper =
+    // Type-check pat1 with the original warnOnUpper flag (to warn on uppercase identifiers)
+    let pat1R, patEnv1 = TcPat warnOnUpper cenv env None vFlags patEnv ty pat1
+
+    // For pat2 (the binding variable like UppercaseIdentifier as Foo), suppress uppercase warnings if the feature is enabled
+    let warnOnUpperForPat2 =
         if cenv.g.langVersion.SupportsFeature(LanguageFeature.DontWarnOnUppercaseIdentifiersInBindingPatterns) then
             AllIdsOK
         else
             warnOnUpper
-
-    let patsR, patEnvR = TcPatterns warnOnUpper cenv env vFlags patEnv (List.map (fun _ -> ty) pats) pats
-    let phase2 values = TPat_conjs(List.map (fun f -> f values) patsR, m)
+    
+    let pat2R, patEnvR = TcPat warnOnUpperForPat2 cenv env None vFlags patEnv1 ty pat2
+    let phase2 values = TPat_conjs([pat1R values; pat2R values], m)
     phase2, patEnvR
 
 and TcPatNamed warnOnUpper cenv env vFlags patEnv id ty isMemberThis vis valReprInfo m =

src/Compiler/SyntaxTree/SyntaxTree.fs

@@ -1057,7 +1057,7 @@ type SynMatchClause =
 
     member this.IsTrueMatchClause =
         let (SynMatchClause(trivia = trivia)) = this
-        trivia.BarRange.IsSome && trivia.ArrowRange.IsSome
+        trivia.ArrowRange.IsSome
 
     member this.Range =
         match this with

tests/FSharp.Compiler.ComponentTests/Conformance/Expressions/BindingExpressions/BindingExpressions.fs

@@ -198,4 +198,10 @@ module BindingExpressions =
         |> asExe        
         |> withOptions ["--test:ErrorRanges"]
         |> typecheck
-        |> shouldSucceed
+        |> shouldFail
+        |> withDiagnostics [
+            (Warning 49, Line 61, Col 6, Line 61, Col 8, "Uppercase variable identifiers should not generally be used in patterns, and may indicate a missing open declaration or a misspelt pattern name.");
+            (Warning 49, Line 122, Col 6, Line 122, Col 8, "Uppercase variable identifiers should not generally be used in patterns, and may indicate a missing open declaration or a misspelt pattern name.");
+            (Warning 49, Line 125, Col 6, Line 125, Col 8, "Uppercase variable identifiers should not generally be used in patterns, and may indicate a missing open declaration or a misspelt pattern name.");
+            (Warning 49, Line 128, Col 6, Line 128, Col 8, "Uppercase variable identifiers should not generally be used in patterns, and may indicate a missing open declaration or a misspelt pattern name.")
+        ]

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/Union/Union.fs

@@ -34,6 +34,10 @@ let customerId = CustomerId("123")
 match customerId with
 | CustomerId BBB -> ()
 
+match 42 with | UpperCase -> ()
+
+match 42 with UpperCase -> ()
+
 type Record = { Name: string; Age: int }
 
 match { Name = "Alice"; Age = 30 } with

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/Union/UpperUnionCasePattern.fs renamed to tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/Union/UpperUnionCasePattern01.fs

@@ -0,0 +1,27 @@
+
+let test1 x =
+    match x with
+    | UndefinedCase -> 1
+
+let test2 x =
+    match x with UndefinedCase -> 1
+
+let test3 = function | UndefinedCase -> 1
+
+let test4 = function UndefinedCase -> 1
+
+let test5 () =
+    try failwith "test"
+    with | UndefinedException -> 1
+    
+let test6 () =
+    try failwith "test"  
+    with UndefinedException -> 1
+
+let test7 () =
+    try failwith "test"  
+    with UndefinedException as Foo -> 1
+
+let test8 () =
+    try failwith "test"  
+    with | UndefinedException as Foo -> 1

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/Union/UpperUnionCasePattern02.fs

@@ -1,3 +1,5 @@
+neg07.fs(7,10,7,29): typecheck error FS0049: Uppercase variable identifiers should not generally be used in patterns, and may indicate a missing open declaration or a misspelt pattern name.
+
 neg07.fs(24,13,24,23): typecheck error FS0039: The value or constructor 'UnionCase1' is not defined. Maybe you want one of the following:
    X.UnionCase1