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Implement interpolated strings via String.Concat #19971

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Merged
T-Gro merged 17 commits into from
Aug 1, 2026
Merged

Implement interpolated strings via String.Concat #19971

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f571df9
Lower string-typed interpolation to String.Concat (reflection-free)
charlesroddie Jun 18, 2026
423d007
Add release notes for interpolated string String.Concat lowering
charlesroddie Jun 18, 2026
c7beb02
tidy
charlesroddie Jun 19, 2026
1951198
Lower string interpolation by type-checking each part in place
charlesroddie Jun 20, 2026
3d5bb3d
cleanup
charlesroddie Jun 20, 2026
5eae16c
Pass a bare %s through as a string instead of via sprintf
charlesroddie Jun 20, 2026
b278961
%s is AOT compatible now
charlesroddie Jun 20, 2026
e83ddfb
Type-check formatted interpolation holes only once
charlesroddie Jun 20, 2026
6112fd2
Lower bare %c/%d/%i/%M interpolation holes to String.Concat
charlesroddie Jun 20, 2026
7d2a246
Check NativeAOT interpolated-string output against expected values
charlesroddie Jun 22, 2026
e87b12f
Add EmittedIL tests for interpolation cases not optimized before
charlesroddie Jun 22, 2026
42e84bb
Merge remote-tracking branch 'upstream/main' into InterpolatedStringC…
charlesroddie Jul 30, 2026
c36ae55
Use the shared mkStringConcat helper for interpolation lowering
charlesroddie Jul 30, 2026
930d2ad
Keep parens around a dangling hole with an alignment
charlesroddie Jul 30, 2026
7163857
Accept a nullable string in a '%s' interpolation hole
charlesroddie Jul 30, 2026
55d2c6b
Format ParseHelpers.fs
charlesroddie Jul 30, 2026
df0ef58
Update expected trimmed sizes for the interpolation codegen change
charlesroddie Jul 30, 2026
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tidy
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@charlesroddie
charlesroddie committed Jun 19, 2026
commit c7beb02d6f1a2a1de197f0e43d346171f9273a5c
10 changes: 5 additions & 5 deletions src/Compiler/Checking/Expressions/CheckExpressions.fs
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Expand Up @@ -7587,11 +7587,11 @@ and TcInterpolatedStringViaConcat (cenv: cenv, overallTy: OverallTy, env: TcEnv,
mkSynApp1 (mkSynLidGet mSynth [ "System"; "String" ] "Format") args mSynth

// Build one string expression per part, consuming one 'holeIsString' flag per fill expression.
let rec build acc parts (holeIsString: bool list) =
let rec build (acc: SynExpr list, parts: SynInterpolatedStringPart list, holeIsString: bool list) =
match parts with
| [] -> List.rev acc
| SynInterpolatedStringPart.String ("", _) :: rest -> build acc rest holeIsString
| SynInterpolatedStringPart.String (s, _) :: rest -> build (strLit (s.Replace("%%", "%")) :: acc) rest holeIsString
| SynInterpolatedStringPart.String ("", _) :: rest -> build (acc, rest, holeIsString)
| SynInterpolatedStringPart.String (s, _) :: rest -> build (strLit (s.Replace("%%", "%")) :: acc, rest, holeIsString)
| SynInterpolatedStringPart.FillExpr (e, formatting) :: rest ->
let isStr, rest' = match holeIsString with b :: bs -> b, bs | [] -> false, []
let argExpr =
Expand All @@ -7600,9 +7600,9 @@ and TcInterpolatedStringViaConcat (cenv: cenv, overallTy: OverallTy, env: TcEnv,
| SynInterpolationFormatting.DotNet (None, None) -> if isStr then e else stringOp e
| SynInterpolationFormatting.DotNet (alignment, format) -> stringFormatOp (alignment, format, e)
| SynInterpolationFormatting.Printf (spec, _) -> sprintfOp (spec, e)
build (argExpr :: acc) rest rest'
build (argExpr :: acc, rest, rest')

let argExprs = build [] parts holeIsString
let argExprs = build ([], parts, holeIsString)

let concatLid = mkSynLidGet mSynth [ "System"; "String" ] "Concat"

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