[RFC FS-1132] Interpolated strings syntax with multiple dollar signs

src/Compiler/Checking/CheckFormatStrings.fs

@@ -72,16 +72,28 @@ let makeFmts (context: FormatStringCheckContext) (fragRanges: range list) (fmt:
     let sourceText = context.SourceText
     let lineStartPositions = context.LineStartPositions
 
+    // Number of curly braces required to delimiter interpolation holes
+    // = Number of $ chars starting a (triple quoted) string literal
+    // Set when we process first fragment range, default = 1
+    let mutable delimLen = 1
+
     let mutable nQuotes = 1
     [ for i, r in List.indexed fragRanges do
         if r.StartLine - 1 < lineStartPositions.Length && r.EndLine - 1 < lineStartPositions.Length then
             let startIndex = lineStartPositions[r.StartLine - 1] + r.StartColumn
             let rLength = lineStartPositions[r.EndLine - 1] + r.EndColumn - startIndex
             let offset =
                 if i = 0 then
-                    match sourceText.GetSubTextString(startIndex, rLength) with
-                    | PrefixedBy "$\"\"\"" len
-                    | PrefixedBy "\"\"\"" len ->
+                    let fullRangeText = sourceText.GetSubTextString(startIndex, rLength)
+                    delimLen <-
+                        fullRangeText
+                        |> Seq.takeWhile (fun c -> c = '$')
+                        |> Seq.length
+                    let tripleQuotePrefix =
+                        [String.replicate delimLen "$"; "\"\"\""]
+                        |> String.concat ""
+                    match fullRangeText with
+                    | PrefixedBy tripleQuotePrefix len ->
                         nQuotes <- 3
                         len
                     | PrefixedBy "$@\"" len
@@ -91,13 +103,13 @@ let makeFmts (context: FormatStringCheckContext) (fragRanges: range list) (fmt:
                     | _ -> 1
                 else
                     1 // <- corresponds to '}' that's closing an interpolation hole
-            let fragLen = rLength - offset - (if i = numFrags - 1 then nQuotes else 1)
+            let fragLen = rLength - offset - (if i = numFrags - 1 then nQuotes else delimLen)
             (offset, sourceText.GetSubTextString(startIndex + offset, fragLen), r)
         else (1, fmt, r)
-    ]
+    ], delimLen
 
 
-module internal Parsing =
+module internal Parse =
 
     let flags (info: FormatInfoRegister) (fmt: string) (fmtPos: int) =
         let len = fmt.Length
@@ -231,10 +243,10 @@ let parseFormatStringInternal
     //
     let escapeFormatStringEnabled = g.langVersion.SupportsFeature Features.LanguageFeature.EscapeDotnetFormattableStrings
 
-    let fmt, fragments =
+    let fmt, fragments, delimLen =
         match context with
         | Some context when fragRanges.Length > 0 ->
-            let fmts = makeFmts context fragRanges fmt
+            let fmts, delimLen = makeFmts context fragRanges fmt
 
             // Join the fragments with holes. Note this join is only used on the IDE path,
             // the CheckExpressions.fs does its own joining with the right alignments etc. substituted
@@ -245,11 +257,11 @@ let parseFormatStringInternal
                 (0, fmts) ||> List.mapFold (fun i (offset, fmt, fragRange) ->
                     (i, offset, fragRange), i + fmt.Length + 4) // the '4' is the length of '%P()' joins
 
-            fmt, fragments
+            fmt, fragments, delimLen
         | _ ->
             // Don't muck with the fmt when there is no source code context to go get the original
             // source code (i.e. when compiling or background checking)
-            (if escapeFormatStringEnabled then escapeDotnetFormatString fmt else fmt), [ (0, 1, m) ]
+            (if escapeFormatStringEnabled then escapeDotnetFormatString fmt else fmt), [ (0, 1, m) ], 1
 
     let len = fmt.Length
 
@@ -299,32 +311,44 @@ let parseFormatStringInternal
 
     and parseSpecifier acc (i, fragLine, fragCol) fragments =
         let startFragCol = fragCol
-        let fragCol = fragCol+1
-        if fmt[i..(i+1)] = "%%" then
+        let nPercentSigns =
+            fmt[i..]
+            |> Seq.takeWhile (fun c -> c = '%')
+            |> Seq.length
+        if delimLen <= 1 && fmt[i..(i+1)] = "%%" then
             match context with
             | Some _ ->
                 specifierLocations.Add(
                     (Range.mkFileIndexRange m.FileIndex
-                        (Position.mkPos fragLine startFragCol)
-                        (Position.mkPos fragLine (fragCol + 1))), 0)
+                        (Position.mkPos fragLine fragCol)
+                        (Position.mkPos fragLine (fragCol+2))), 0)
             | None -> ()
             appendToDotnetFormatString "%"
-            parseLoop acc (i+2, fragLine, fragCol+1) fragments
+            parseLoop acc (i+2, fragLine, fragCol+2) fragments
+        elif delimLen > 1 && nPercentSigns < delimLen then
+            appendToDotnetFormatString fmt[i..(i+nPercentSigns-1)]
+            parseLoop acc (i + nPercentSigns, fragLine, fragCol + nPercentSigns) fragments
         else
-            let i = i+1
+            let fragCol, i =
+                if delimLen > 1 then
+                    if nPercentSigns > delimLen then
+                        "%" |> String.replicate (nPercentSigns - delimLen) |> appendToDotnetFormatString
+                    fragCol + nPercentSigns, i + nPercentSigns
+                else
+                    fragCol + 1, i + 1
             if i >= len then failwith (FSComp.SR.forMissingFormatSpecifier())
             let info = newInfo()
 
             let oldI = i
-            let posi, i = Parsing.position fmt i
+            let posi, i = Parse.position fmt i
             let fragCol = fragCol + i - oldI
 
             let oldI = i
-            let i = Parsing.flags info fmt i
+            let i = Parse.flags info fmt i
             let fragCol = fragCol + i - oldI
 
             let oldI = i
-            let widthArg,(widthValue, (precisionArg,i)) = Parsing.widthAndPrecision info fmt i
+            let widthArg,(widthValue, (precisionArg,i)) = Parse.widthAndPrecision info fmt i
             let fragCol = fragCol + i - oldI
 
             if i >= len then failwith (FSComp.SR.forBadPrecision())
@@ -340,7 +364,7 @@ let parseFormatStringInternal
                 | Some n -> failwith (FSComp.SR.forDoesNotSupportPrefixFlag(c.ToString(), n.ToString()))
                 | None -> ()
 
-            let skipPossibleInterpolationHole pos = Parsing.skipPossibleInterpolationHole isInterpolated isFormattableString fmt pos
+            let skipPossibleInterpolationHole pos = Parse.skipPossibleInterpolationHole isInterpolated isFormattableString fmt pos
 
             // Implicitly typed holes in interpolated strings are translated to '... %P(...)...' in the
             // type checker.  They should always have '(...)' after for format string.

src/Compiler/FSComp.txt

@@ -1122,6 +1122,10 @@ lexIfOCaml,"IF-FSHARP/IF-CAML regions are no longer supported"
 1245,lexInvalidUnicodeLiteral,"\U%s is not a valid Unicode character escape sequence"
 1246,tcCallerInfoWrongType,"'%s' must be applied to an argument of type '%s', but has been applied to an argument of type '%s'"
 1247,tcCallerInfoNotOptional,"'%s' can only be applied to optional arguments"
+1248,lexTooManyLBracesInTripleQuote,"The interpolated triple quoted string literal does not start with enough '$' characters to allow this many consecutive opening braces as content."
+1249,lexUnmatchedRBracesInTripleQuote,"The interpolated string contains unmatched closing braces."
+1250,lexTooManyPercentsInTripleQuote,"The interpolated triple quoted string literal does not start with enough '$' characters to allow this many consecutive '%%' characters."
+1251,lexExtendedStringInterpolationNotSupported,"Extended string interpolation is not supported in this version of F#."
 # reshapedmsbuild.fs
 1300,toolLocationHelperUnsupportedFrameworkVersion,"The specified .NET Framework version '%s' is not supported. Please specify a value from the enumeration Microsoft.Build.Utilities.TargetDotNetFrameworkVersion."
 # -----------------------------------------------------------------------------
@@ -1567,6 +1571,7 @@ featureWarningWhenCopyAndUpdateRecordChangesAllFields,"Raises warnings when an c
 featureStaticMembersInInterfaces,"Static members in interfaces"
 featureNonInlineLiteralsAsPrintfFormat,"String values marked as literals and IL constants as printf format"
 featureNestedCopyAndUpdate,"Nested record field copy-and-update"
+featureExtendedStringInterpolation,"Extended string interpolation similar to C# raw string literals."
 3353,fsiInvalidDirective,"Invalid directive '#%s %s'"
 3354,tcNotAFunctionButIndexerNamedIndexingNotYetEnabled,"This value supports indexing, e.g. '%s.[index]'. The syntax '%s[index]' requires /langversion:preview. See https://aka.ms/fsharp-index-notation."
 3354,tcNotAFunctionButIndexerIndexingNotYetEnabled,"This expression supports indexing, e.g. 'expr.[index]'. The syntax 'expr[index]' requires /langversion:preview. See https://aka.ms/fsharp-index-notation."

src/Compiler/Facilities/LanguageFeatures.fs

@@ -66,6 +66,7 @@ type LanguageFeature =
     | StaticMembersInInterfaces
     | NonInlineLiteralsAsPrintfFormat
     | NestedCopyAndUpdate
+    | ExtendedStringInterpolation
 
 /// LanguageVersion management
 type LanguageVersion(versionText) =
@@ -155,6 +156,7 @@ type LanguageVersion(versionText) =
                 LanguageFeature.StaticMembersInInterfaces, previewVersion
                 LanguageFeature.NonInlineLiteralsAsPrintfFormat, previewVersion
                 LanguageFeature.NestedCopyAndUpdate, previewVersion
+                LanguageFeature.ExtendedStringInterpolation, previewVersion
 
             ]
 
@@ -276,6 +278,7 @@ type LanguageVersion(versionText) =
         | LanguageFeature.StaticMembersInInterfaces -> FSComp.SR.featureStaticMembersInInterfaces ()
         | LanguageFeature.NonInlineLiteralsAsPrintfFormat -> FSComp.SR.featureNonInlineLiteralsAsPrintfFormat ()
         | LanguageFeature.NestedCopyAndUpdate -> FSComp.SR.featureNestedCopyAndUpdate ()
+        | LanguageFeature.ExtendedStringInterpolation -> FSComp.SR.featureExtendedStringInterpolation ()
 
     /// Get a version string associated with the given feature.
     static member GetFeatureVersionString feature =

src/Compiler/Facilities/LanguageFeatures.fsi

@@ -56,6 +56,7 @@ type LanguageFeature =
     | StaticMembersInInterfaces
     | NonInlineLiteralsAsPrintfFormat
     | NestedCopyAndUpdate
+    | ExtendedStringInterpolation
 
 /// LanguageVersion management
 type LanguageVersion =

src/Compiler/Service/FSharpCheckerResults.fs

@@ -2352,15 +2352,19 @@ module internal ParseAndCheckFile =
 
             let rec matchBraces stack =
                 match lexfun lexbuf, stack with
-                | tok2, (tok1, m1) :: stackAfterMatch when parenTokensBalance tok1 tok2 ->
+                | tok2, (tok1, braceOffset, m1) :: stackAfterMatch when parenTokensBalance tok1 tok2 ->
                     let m2 = lexbuf.LexemeRange
 
                     // For INTERP_STRING_PART and INTERP_STRING_END grab the one character
                     // range that corresponds to the "}" at the start of the token
                     let m2Start =
                         match tok2 with
                         | INTERP_STRING_PART _
-                        | INTERP_STRING_END _ -> mkFileIndexRange m2.FileIndex m2.Start (mkPos m2.Start.Line (m2.Start.Column + 1))
+                        | INTERP_STRING_END _ ->
+                            mkFileIndexRange
+                                m2.FileIndex
+                                (mkPos m2.Start.Line (m2.Start.Column - braceOffset))
+                                (mkPos m2.Start.Line (m2.Start.Column + 1))
                         | _ -> m2
 
                     matchingBraces.Add(m1, m2Start)
@@ -2371,15 +2375,15 @@ module internal ParseAndCheckFile =
                         match tok2 with
                         | INTERP_STRING_PART _ ->
                             let m2End =
-                                mkFileIndexRange m2.FileIndex (mkPos m2.End.Line (max (m2.End.Column - 1) 0)) m2.End
+                                mkFileIndexRange m2.FileIndex (mkPos m2.End.Line (max (m2.End.Column - 1 - braceOffset) 0)) m2.End
 
-                            (tok2, m2End) :: stackAfterMatch
+                            (tok2, braceOffset, m2End) :: stackAfterMatch
                         | _ -> stackAfterMatch
 
                     matchBraces stackAfterMatch
 
                 | LPAREN | LBRACE _ | LBRACK | LBRACE_BAR | LBRACK_BAR | LQUOTE _ | LBRACK_LESS as tok, _ ->
-                    matchBraces ((tok, lexbuf.LexemeRange) :: stack)
+                    matchBraces ((tok, 0, lexbuf.LexemeRange) :: stack)
 
                 // INTERP_STRING_BEGIN_PART corresponds to $"... {" at the start of an interpolated string
                 //
@@ -2389,12 +2393,18 @@ module internal ParseAndCheckFile =
                 //
                 // Either way we start a new potential match at the last character
                 | INTERP_STRING_BEGIN_PART _ | INTERP_STRING_PART _ as tok, _ ->
+                    let braceOffset =
+                        match tok with
+                        | INTERP_STRING_BEGIN_PART (_, SynStringKind.TripleQuote, (LexerContinuation.Token (_, (_, _, dl, _) :: _))) ->
+                            dl - 1
+                        | _ -> 0
+
                     let m = lexbuf.LexemeRange
 
                     let m2 =
-                        mkFileIndexRange m.FileIndex (mkPos m.End.Line (max (m.End.Column - 1) 0)) m.End
+                        mkFileIndexRange m.FileIndex (mkPos m.End.Line (max (m.End.Column - 1 - braceOffset) 0)) m.End
 
-                    matchBraces ((tok, m2) :: stack)
+                    matchBraces ((tok, braceOffset, m2) :: stack)
 
                 | (EOF _ | LEX_FAILURE _), _ -> ()
                 | _ -> matchBraces stack