Add regression test: #6929, Literal bindings preserve units of measure (#19463)

* Add regression test for #6929: Literal bindings preserve units of measure

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Fix: use local shouldSucceed wrapper instead of redundant pipeline

The test was calling asLibrary |> typecheck |> shouldSucceed, but the local
shouldSucceed function (which already does asLibrary/typecheck) was shadowing
FSharp.Test.Compiler.shouldSucceed, causing a type mismatch (FS0001).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: T-Gro

.github/instructions/ComponentTests.instructions.md

@@ -0,0 +1,132 @@
+---
+applyTo:
+  - "tests/FSharp.Compiler.ComponentTests/**/*.fs"
+---
+
+# ComponentTests DSL
+
+Tests use a pipeline: **Create → Configure → Action → Assert**. The action verb is mandatory — never pipe a `CompilationUnit` directly into an assertion.
+
+## Actions (pick the cheapest that covers what you're testing)
+
+```fsharp
+// Type errors only, no codegen — fastest
+FSharp "..."
+|> typecheck
+|> shouldSucceed
+
+// Full compile, produces assembly
+FSharp "..."
+|> compile
+|> shouldSucceed
+
+// IL shape verification (needs compile)
+FSharp "..."
+|> compile
+|> verifyILContains [".method"]
+
+// Compile + execute (needs EntryPoint and asExe)
+FSharp "..."
+|> compileExeAndRun
+|> shouldSucceed
+
+// FSI in-process
+Fsx "..."
+|> eval
+|> withEvalValueEquals 2
+
+// FSI subprocess
+Fsx "..."
+|> runFsi
+|> withStdOutContains "hello"
+```
+
+Use `typecheck` for anything that doesn't need IL or runtime. Use `compile` only when you need the assembly (IL checks, interop). Use `compileExeAndRun` only when testing runtime behavior.
+
+## Diagnostics
+
+```fsharp
+// Exact diagnostic with location and message
+FSharp "..."
+|> typecheck
+|> shouldFail
+|> withDiagnostics [
+    (Error 73, Line 3, Col 5, Line 3, Col 10, "internal error: ...")
+    (Warning 20, Line 5, Col 1, Line 5, Col 8, "The result of this expression...")
+]
+
+// Just error code (when message/location don't matter)
+FSharp "..."
+|> typecheck
+|> shouldFail
+|> withErrorCode 73
+```
+
+## C# interop
+
+```fsharp
+let csLib =
+    CSharp """public interface I { void M(out int v); }"""
+    |> withName "CsLib"
+
+FSharp """
+open CsLib
+type T() = interface I with member _.M(v) = v <- 42
+"""
+|> withReferences [csLib]
+|> compile
+|> shouldSucceed
+```
+
+## Regression test template
+
+```fsharp
+// https://github.com/dotnet/fsharp/issues/NNNNN
+[<Fact>]
+let ``Issue NNNNN - brief description`` () =
+    FSharp """
+// minimal repro from issue
+    """
+    |> asLibrary
+    |> typecheck
+    |> shouldSucceed
+```
+
+## Local helpers
+
+If configuration becomes long and boilerplate, extract a local helper or use an existing one in the same module:
+
+```fsharp
+// Local helper for repeated configuration
+let typecheckWithPreview source =
+    source
+    |> asLibrary
+    |> withLangVersionPreview
+    |> withOptions ["--test:ErrorRanges"]
+    |> typecheck
+
+// Usage
+FSharp "..."
+|> typecheckWithPreview
+|> shouldSucceed
+```
+
+## Common mistakes
+
+- Missing action: `FSharp "..." |> shouldSucceed` — won't compile, `shouldSucceed` expects `CompilationResult`
+- Missing `asExe` for runtime tests: `FSharp "..." |> compile |> run` fails on library output
+- Using `compile` when `typecheck` suffices — wastes CI time
+
+## Platform attributes
+
+Use `[<Fact>]` unless the test requires a specific runtime:
+- `[<FactForNETCOREAPP>]` — .NET Core only
+- `[<FactForDESKTOP>]` — .NET Framework only
+- `[<FactForWINDOWS>]` — Windows only
+
+## Workflow
+
+1. Write test with explicit pipeline
+2. Build: `dotnet build tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj -c Release`
+3. Run: `dotnet test --project tests/FSharp.Compiler.ComponentTests/FSharp.Compiler.ComponentTests.fsproj -c Release --no-build -- --filter-method "*TestName*"`
+4. Format: `dotnet fantomas <file.fs>`

tests/FSharp.Compiler.ComponentTests/Conformance/UnitsOfMeasure/Constants/Constants.fs

@@ -40,3 +40,20 @@ module Constants =
             (Error 636, Line 22, Col 9, Line 22, Col 15, "Units-of-measure are only supported on float, float32, decimal, and integer types.")
             (Error 636, Line 23, Col 9, Line 23, Col 15, "Units-of-measure are only supported on float, float32, decimal, and integer types.")
         ]
+
+    // https://github.com/dotnet/fsharp/issues/6929
+    [<Fact>]
+    let ``Issue 6929 - Literal bindings preserve units of measure`` () =
+        FSharp
+            """
+[<Measure>] type rad
+
+[<Literal>]
+let pi = 3.14<rad>
+
+let a = pi
+
+let f (x: float<rad>) = x
+let _ = f a
+            """
+        |> shouldSucceed