Fix parsing interpolated strings with unmatched braces (#14182)

* Pop string nesting before error in nested quotes

* Cover more cases of incomplete interpolation

* Add tests for unmatched curly brace

Two tests for unmatched curly brace in interpolated string

* Split tests into separate cases

This splits two unit tests that were testing multiple cases in one go
into multiple unit tests - one per each case.

Note, that original tests were expecting an accurate error for each
of multiple lines of malformed string literals. They would no longer
pass with changes introduced by previous commits in this PR.
Co-authored-by: NAdam Boniecki <adboniec@microsoft.com>

src/Compiler/lex.fsl

@@ -601,7 +601,9 @@ rule token args skip = parse
        // Single quote in triple quote ok, others disallowed
        match args.stringNest with
        | (_, LexerStringStyle.TripleQuote, _) :: _ -> ()
-       | _ :: _ -> errorR(Error(FSComp.SR.lexSingleQuoteInSingleQuote(), m))
+       | _ :: rest ->
+           args.stringNest <- rest
+           errorR(Error(FSComp.SR.lexSingleQuoteInSingleQuote(), m))
        | [] -> ()
 
        if not skip then STRING_TEXT (LexCont.String(args.ifdefStack, args.stringNest, LexerStringStyle.SingleQuote, LexerStringKind.String, m))
@@ -612,7 +614,9 @@ rule token args skip = parse
 
        // Single quote in triple quote ok, others disallowed
        match args.stringNest with
-       | _ :: _ -> errorR(Error(FSComp.SR.lexTripleQuoteInTripleQuote(), m))
+       | _ :: rest ->
+           args.stringNest <- rest
+           errorR(Error(FSComp.SR.lexTripleQuoteInTripleQuote(), m))
        | [] -> ()
 
        if not skip then STRING_TEXT (LexCont.String(args.ifdefStack, args.stringNest, LexerStringStyle.TripleQuote, LexerStringKind.InterpolatedStringFirst, m))
@@ -624,7 +628,9 @@ rule token args skip = parse
        // Single quote in triple quote ok, others disallowed
        match args.stringNest with
        | (_, LexerStringStyle.TripleQuote, _) :: _ -> ()
-       | _ :: _ -> errorR(Error(FSComp.SR.lexSingleQuoteInSingleQuote(), m))
+       | _ :: rest ->
+           args.stringNest <- rest
+           errorR(Error(FSComp.SR.lexSingleQuoteInSingleQuote(), m))
        | _ -> ()
 
        if not skip then STRING_TEXT (LexCont.String(args.ifdefStack, args.stringNest, LexerStringStyle.SingleQuote, LexerStringKind.InterpolatedStringFirst, m))
@@ -635,7 +641,9 @@ rule token args skip = parse
 
        // Single quote in triple quote ok, others disallowed
        match args.stringNest with
-       | _ :: _ -> errorR(Error(FSComp.SR.lexTripleQuoteInTripleQuote(), m))
+       | _ :: rest ->
+           args.stringNest <- rest
+           errorR(Error(FSComp.SR.lexTripleQuoteInTripleQuote(), m))
        | _ -> ()
 
        if not skip then STRING_TEXT (LexCont.String(args.ifdefStack, args.stringNest, LexerStringStyle.TripleQuote, LexerStringKind.String, m))
@@ -647,7 +655,9 @@ rule token args skip = parse
        // Single quote in triple quote ok, others disallowed
        match args.stringNest with
        | (_, LexerStringStyle.TripleQuote, _) :: _ -> ()
-       | _ :: _ -> errorR(Error(FSComp.SR.lexSingleQuoteInSingleQuote(), m))
+       | _ :: rest ->
+           args.stringNest <- rest
+           errorR(Error(FSComp.SR.lexSingleQuoteInSingleQuote(), m))
        | _ -> ()
 
        if not skip then STRING_TEXT (LexCont.String(args.ifdefStack, args.stringNest, LexerStringStyle.Verbatim, LexerStringKind.String, m))
@@ -659,7 +669,9 @@ rule token args skip = parse
        // Single quote in triple quote ok, others disallowed
        match args.stringNest with
        | (_, LexerStringStyle.TripleQuote, _) :: _ -> ()
-       | _ :: _ -> errorR(Error(FSComp.SR.lexSingleQuoteInSingleQuote(), m))
+       | _ :: rest ->
+           args.stringNest <- rest
+           errorR(Error(FSComp.SR.lexSingleQuoteInSingleQuote(), m))
        | _ -> ()
 
        if not skip then STRING_TEXT (LexCont.String(args.ifdefStack, args.stringNest, LexerStringStyle.Verbatim, LexerStringKind.InterpolatedStringFirst, m))

tests/fsharp/Compiler/Language/StringInterpolation.fs

@@ -730,70 +730,50 @@ let x3 : FormattableString = $"one %10s{String.Empty}" // no %10s in Formattable
               (FSharpDiagnosticSeverity.Error, 3376, (6, 30, 6, 55),
                "Invalid interpolated string. Interpolated strings used as type IFormattable or type FormattableString may not use '%' specifiers, only .NET-style interpolands such as '{expr}', '{expr,3}' or '{expr:N5}' may be used.")|]
 
-
-    [<Test>]
-    let ``String interpolation negative nested in single`` () =
-        let code =    """
-
-open System 
-let s1 = $"123{456}789{"012"}345" 
-let s2 = $"123{456}789{@"012"}345" 
-let s3 = $"123{456}789{$"012"}345" 
-let s4 = $@"123{456}789{"012"}345" 
-let s5 = @$"123{456}789{"012"}345" 
-let s6 = $@"123{456}789{@"012"}345" 
-let s7 = @$"123{456}789{$"012"}345" 
-let s8 = $@"123{456}789{@$"012"}345" 
-let s9 = @$"123{456}789{$@"012"}345" 
-"""
-        CompilerAssert.TypeCheckWithErrorsAndOptions  [| "--langversion:5.0" |]
+    [<TestCase("""let s1 = $"123{456}789{""",    "\"012\"", "}345\"")>]
+    [<TestCase("""let s2 = $"123{456}789{""",   "@\"012\"", "}345\"")>]
+    [<TestCase("""let s3 = $"123{456}789{""",   "$\"012\"", "}345\"")>]
+    [<TestCase("""let s4 = $@"123{456}789{""",   "\"012\"", "}345\"")>]
+    [<TestCase("""let s5 = @$"123{456}789{""",   "\"012\"", "}345\"")>]
+    [<TestCase("""let s6 = $@"123{456}789{""",  "@\"012\"", "}345\"")>]
+    [<TestCase("""let s7 = @$"123{456}789{""",  "$\"012\"", "}345\"")>]
+    [<TestCase("""let s8 = $@"123{456}789{""", "@$\"012\"", "}345\"")>]
+    [<TestCase("""let s9 = @$"123{456}789{""", "$@\"012\"", "}345\"")>]
+    let ``String interpolation negative nested in single`` ((part1: string, expr: string, part2: string)) =
+        let code = part1 + expr + part2
+        let exprPosBegin = 1 + part1.Length
+        let quotePosInExpr = exprPosBegin + (expr |> Seq.findIndex (fun c -> c = '"'))
+        let closingBracePos = exprPosBegin + expr.Length
+        CompilerAssert.TypeCheckWithErrorsAndOptions [| "--langversion:5.0" |]
             code
-            [|(FSharpDiagnosticSeverity.Error, 3373, (4, 24, 4, 25),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
-              (FSharpDiagnosticSeverity.Error, 3373, (5, 24, 5, 26),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
-              (FSharpDiagnosticSeverity.Error, 3373, (6, 24, 6, 26),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
-              (FSharpDiagnosticSeverity.Error, 3373, (7, 25, 7, 26),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
-              (FSharpDiagnosticSeverity.Error, 3373, (8, 25, 8, 26),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
-              (FSharpDiagnosticSeverity.Error, 3373, (9, 25, 9, 27),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
-              (FSharpDiagnosticSeverity.Error, 3373, (10, 25, 10, 27),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
-              (FSharpDiagnosticSeverity.Error, 3373, (11, 25, 11, 28),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
-              (FSharpDiagnosticSeverity.Error, 3373, (12, 25, 12, 28),
-               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.")|]
-
-    [<Test>]
-    let ``String interpolation negative nested in triple`` () =
-        let code =    "
-
-open System 
-let TripleInTripleInterpolated   = $\"\"\"123{456}789{\"\"\"012\"\"\"}345\"\"\" 
-let TripleInSingleInterpolated   = $\"123{456}789{\"\"\"012\"\"\"}345\" 
-let TripleInVerbatimInterpolated = $\"123{456}789{\"\"\"012\"\"\"}345\" 
-let TripleInterpolatedInTripleInterpolated   = $\"\"\"123{456}789{$\"\"\"012\"\"\"}345\"\"\" 
-let TripleInterpolatedInSingleInterpolated   = $\"123{456}789{$\"\"\"012\"\"\"}345\" 
-let TripleInterpolatedInVerbatimInterpolated = $\"123{456}789{$\"\"\"012\"\"\"}345\" 
-"
+            [|(FSharpDiagnosticSeverity.Error, 3373, (1, exprPosBegin, 1, quotePosInExpr + 1),
+               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. \
+               Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
+              (FSharpDiagnosticSeverity.Error, 10, (1, closingBracePos, 1, closingBracePos + 1),
+               "Unexpected symbol '}' in binding. Expected interpolated string (final part), interpolated string (part) or other token.");
+              (FSharpDiagnosticSeverity.Error, 514, (1, code.Length, 1, code.Length + 1), "End of file in string begun at or before here")|]
+
+    [<TestCase("let TripleInTripleInterpolated = $\"\"\"123{456}789{",              "\"\"\"012\"\"\"", "}345\"\"\"")>]
+    [<TestCase("let TripleInSingleInterpolated = $\"123{456}789{",                  "\"\"\"012\"\"\"", "}345\"\"\"")>]
+    [<TestCase("let TripleInVerbatimInterpolated = @$\"123{456}789{",               "\"\"\"012\"\"\"", "}345\"\"\"")>]
+    [<TestCase("let TripleInterpolatedInTripleInterpolated = $\"\"\"123{456}789{", "$\"\"\"012\"\"\"", "}345\"\"\"")>]
+    [<TestCase("let TripleInterpolatedInSingleInterpolated = $\"123{456}789{",     "$\"\"\"012\"\"\"", "}345\"\"\"")>]
+    [<TestCase("let TripleInterpolatedInVerbatimInterpolated = @$\"123{456}789{",  "$\"\"\"012\"\"\"", "}345\"\"\"")>]
+    let ``String interpolation negative nested in triple`` ((part1: string, expr: string, part2: string)) =
+        let code = part1 + expr + part2
+        let exprPosBegin = 1 + part1.Length
+        let exprOpenQuoteEnd = exprPosBegin + 3 + (expr |> Seq.takeWhile (fun c -> c <> '"') |> Seq.length)
+        let closingBracePos = exprPosBegin + expr.Length
+        let closingQuotePos = code.Length + 1 - 3
         CompilerAssert.TypeCheckWithErrorsAndOptions  [| "--langversion:5.0" |]
             code
-            [|(FSharpDiagnosticSeverity.Error, 3374, (4, 52, 4, 55),
-               "Invalid interpolated string. Triple quote string literals may not be used in interpolated expressions. Consider using an explicit 'let' binding for the interpolation expression.");
-              (FSharpDiagnosticSeverity.Error, 3374, (5, 50, 5, 53),
-               "Invalid interpolated string. Triple quote string literals may not be used in interpolated expressions. Consider using an explicit 'let' binding for the interpolation expression.");
-              (FSharpDiagnosticSeverity.Error, 3374, (6, 50, 6, 53),
+            [|(FSharpDiagnosticSeverity.Error, 3374, (1, exprPosBegin, 1, exprOpenQuoteEnd),
                "Invalid interpolated string. Triple quote string literals may not be used in interpolated expressions. Consider using an explicit 'let' binding for the interpolation expression.");
-              (FSharpDiagnosticSeverity.Error, 3374, (7, 64, 7, 68),
-               "Invalid interpolated string. Triple quote string literals may not be used in interpolated expressions. Consider using an explicit 'let' binding for the interpolation expression.");
-              (FSharpDiagnosticSeverity.Error, 3374, (8, 62, 8, 66),
-               "Invalid interpolated string. Triple quote string literals may not be used in interpolated expressions. Consider using an explicit 'let' binding for the interpolation expression.");
-              (FSharpDiagnosticSeverity.Error, 3374, (9, 62, 9, 66),
-               "Invalid interpolated string. Triple quote string literals may not be used in interpolated expressions. Consider using an explicit 'let' binding for the interpolation expression.")|]
-  
+              (FSharpDiagnosticSeverity.Error, 10, (1, closingBracePos, 1, closingBracePos + 1),
+               "Unexpected symbol '}' in binding. Expected interpolated string (final part), interpolated string (part) or other token.");
+              (FSharpDiagnosticSeverity.Error, 1232, (1, closingQuotePos, 1, closingQuotePos + 3),
+               "End of file in triple-quote string begun at or before here")|]
+
     [<Test>]
     let ``String interpolation negative incomplete string`` () =
         let code =    """let x1 = $"one %d{System.String.Empty}"""
@@ -803,9 +783,9 @@ let TripleInterpolatedInVerbatimInterpolated = $\"123{456}789{$\"\"\"012\"\"\"}3
                "Incomplete structured construct at or before this point in binding. Expected interpolated string (final part), interpolated string (part) or other token.");
               (FSharpDiagnosticSeverity.Error, 3379, (1, 38, 1, 39),
                "Incomplete interpolated string begun at or before here")|]
-  
+
     [<Test>]
-    let ``String interpolation negative incomplete string fill`` () =
+    let ``String interpolation negative incomplete string with incomplete fill`` () =
         let code =    """let x1 = $"one %d{System.String.Empty"""
         CompilerAssert.TypeCheckWithErrorsAndOptions  [| "--langversion:5.0" |]
             code
@@ -813,7 +793,36 @@ let TripleInterpolatedInVerbatimInterpolated = $\"123{456}789{$\"\"\"012\"\"\"}3
                "Incomplete structured construct at or before this point in binding. Expected interpolated string (final part), interpolated string (part) or other token.");
               (FSharpDiagnosticSeverity.Error, 3378, (1, 18, 1, 19),
                "Incomplete interpolated string expression fill begun at or before here")|]
-  
+
+    [<Test>]
+    let ``String interpolation negative incomplete fill`` () =
+        let code =    "let x1 = $\"one %d{System.String.Empty\""
+        CompilerAssert.TypeCheckWithErrorsAndOptions  [| "--langversion:5.0" |]
+            code
+            [|(FSharpDiagnosticSeverity.Error, 3373, (1, 38, 1, 39),
+               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. \
+               Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
+              (FSharpDiagnosticSeverity.Error, 10, (1, 1, 1, 39),
+               "Incomplete structured construct at or before this point in binding. Expected interpolated string (final part), interpolated string (part) or other token.");
+              (FSharpDiagnosticSeverity.Error, 514, (1, 38, 1, 39),
+               "End of file in string begun at or before here")|]
+
+    [<Test>]
+    let ``String interpolation negative incomplete fill with another valid string`` () =
+        let code = """
+let x1 = $"one %d{System.String.Empty"
+let x2 = "any old string"
+"""
+        CompilerAssert.TypeCheckWithErrorsAndOptions  [| "--langversion:5.0" |]
+            code
+            [|(FSharpDiagnosticSeverity.Error, 3373, (2, 38, 2, 39),
+               "Invalid interpolated string. Single quote or verbatim string literals may not be used in interpolated expressions in single quote or verbatim strings. \
+               Consider using an explicit 'let' binding for the interpolation expression or use a triple quote string as the outer string literal.");
+              (FSharpDiagnosticSeverity.Error, 10, (4, 1, 4, 1),
+               "Incomplete structured construct at or before this point in binding. Expected interpolated string (final part), interpolated string (part) or other token.");
+              (FSharpDiagnosticSeverity.Error, 514, (3, 25, 3, 26),
+               "End of file in string begun at or before here")|]
+
     [<Test>]
     let ``String interpolation negative incomplete verbatim string`` () =
         let code =    """let x1 = @$"one %d{System.String.Empty} """