Fix units-of-measure changes not invalidating incremental builds (#19050)

Author: Copilot

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

@@ -7,6 +7,7 @@
 * 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))  
 * Disallow recursive structs with lifted type parameters ([Issue #18993](https://github.com/dotnet/fsharp/issues/18993), [PR #19031](https://github.com/dotnet/fsharp/pull/19031))
+* Fix units-of-measure changes not invalidating incremental builds. ([Issue #19049](https://github.com/dotnet/fsharp/issues/19049))
 
 ### Added
 

src/Compiler/Utilities/TypeHashing.fs

@@ -188,13 +188,22 @@ module rec HashTypes =
         |> pipeToHash memberHash
 
     /// Hash a unit of measure expression
-    let private hashMeasure unt =
-        let measuresWithExponents =
+    let private hashMeasure g unt =
+        let measureVarsWithExponents =
             ListMeasureVarOccsWithNonZeroExponents unt
             |> List.sortBy (fun (tp: Typar, _) -> tp.DisplayName)
 
-        measuresWithExponents
-        |> hashListOrderIndependent (fun (typar, exp: Rational) -> hashTyparRef typar @@ hash exp)
+        let measureConsWithExponents = ListMeasureConOccsWithNonZeroExponents g false unt
+
+        let varHash =
+            measureVarsWithExponents
+            |> hashListOrderIndependent (fun (typar, exp: Rational) -> hashTyparRef typar @@ hash exp)
+
+        let conHash =
+            measureConsWithExponents
+            |> hashListOrderIndependent (fun (tcref, exp: Rational) -> hashTyconRef tcref @@ hash exp)
+
+        varHash @@ conHash
 
     /// Hash a type, taking precedence into account to insert brackets where needed
     let hashTType (g: TcGlobals) ty =
@@ -217,7 +226,7 @@ module rec HashTypes =
             let argTys, retTy = stripFunTy g ty
             argTys |> hashListOrderMatters (hashTType g) |> pipeToHash (hashTType g retTy)
         | TType_var(r, _) -> hashTyparRefWithInfo r
-        | TType_measure unt -> hashMeasure unt
+        | TType_measure unt -> hashMeasure g unt
 
     // Hash a single argument, including its name and type
     let private hashArgInfo (g: TcGlobals) (ty, argInfo: ArgReprInfo) =

tests/FSharp.Compiler.ComponentTests/Signatures/ImpliedSignatureHashTests.fs

@@ -288,6 +288,16 @@ type BAttribute() =
 
 let a ([<B>] c: int) : int = 0  """)>]
 
+[<InlineDataAttribute("UnitsOfMeasureChanged",
+(*BEFORE*)"""module MyTest
+[<Measure>] type kg
+[<Measure>] type m
+type MyRecord = { Mass: int<kg> }"""
+(*AFTER*),"""module MyTest
+[<Measure>] type kg
+[<Measure>] type m
+type MyRecord = { Mass: int<m> }""")>]
+
 //TODO add a lot more negative tests - in which cases should hash in fact change
 
 [<Theory>]