Fix #2013: Consider true, false as compiler define identifiers. (#2019)

* Consider true, false as compiler define identifiers.

Fix #2013

src/Fantomas.Tests/CompilerDirectivesTests.fs

@@ -2692,3 +2692,26 @@ try
 with
 | _ -> ()
 """
+
+[<Test>]
+let ``should handle #if with boolean constant`` () =
+    formatSourceString
+        false
+        """
+#if false
+let x = 1
+#endif
+#if true
+let x = 1
+#endif
+"""
+        config
+    |> should
+        equal
+        """#if false
+let x = 1
+#endif
+#if true
+let x = 1
+#endif
+"""

src/Fantomas.Tests/TokenParserBoolExprTests.fs

@@ -38,6 +38,28 @@ let x = 1
             )
         ))
 
+let ``Get define exprs from boolean constant`` booleanConstString =
+    let source =
+        (sprintf
+            """
+#if %s
+let x = 1
+#endif
+"""
+            booleanConstString)
+
+    getDefineExprs source
+    |> List.head
+    |> should equal (BoolExpr.Ident booleanConstString)
+
+[<Test>]
+let ``Get define exprs from boolean constant (true)`` () =
+    ``Get define exprs from boolean constant`` "true"
+
+[<Test>]
+let ``Get define exprs from boolean constant (false)`` () =
+    ``Get define exprs from boolean constant`` "false"
+
 [<Test>]
 let ``simple compiler directive - else expr`` () =
     let source =
@@ -212,8 +234,14 @@ type BoolExprGenerator =
     static member SimpleIdent() =
         { new Arbitrary<string>() with
             member x.Generator =
-                Gen.choose (int 'A', int 'Z')
-                |> Gen.map (char >> string)
+                let idents =
+                    Gen.choose (int 'A', int 'Z')
+                    |> Gen.map (char >> string)
+
+                let constants = Gen.elements [ "true"; "false" ]
+
+                Gen.frequency [ 10, idents
+                                1, constants ]
 
             member x.Shrinker t = Seq.empty }
 

src/Fantomas/TokenParser.fs

@@ -373,7 +373,7 @@ and tokenize defines (hashTokens: Token list) (content: string) : Token list =
 
 let getDefinesWords (tokens: Token list) =
     tokens
-    |> List.filter (fun { TokenInfo = { TokenName = tn } } -> tn = "IDENT")
+    |> List.filter (fun { TokenInfo = { TokenName = tn } } -> tn = "IDENT" || tn = "FALSE" || tn = "TRUE")
     |> List.map (fun t -> t.Content)
     |> List.distinct
 
@@ -385,6 +385,8 @@ let getDefineExprs (hashTokens: Token list) =
         |> Seq.filter
             (fun t ->
                 t.TokenInfo.TokenName = "IDENT"
+                || t.TokenInfo.TokenName = "TRUE"
+                || t.TokenInfo.TokenName = "FALSE"
                 || Set.contains t.Content allowedContent)
         |> Seq.map (fun t -> t.Content)
         |> Seq.toList