Implement interpolated strings via String.Concat - #1
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charlesroddie
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A string-typed interpolated string is lowered to System.String.Concat of its parts rather than the reflection-based printf engine: a string-typed hole is passed through directly, any other plain hole is converted with `string x`, an aligned/formatted hole with `String.Format(InvariantCulture, ...)`, and a printf-specifier hole with `sprintf`. This removes the reflection dependency on the common path, so these interpolations become trim- and NativeAOT-compatible. This generalizes and replaces the language-version-gated String.Concat optimization (dotnet#16556), which only handled all-string holes: the lowering now applies to every string-typed interpolation, ungated. The reflection path is used only for PrintfFormat/FormattableString-typed interpolation. The syntax tree now carries each hole's formatting explicitly, so a printf specifier no longer leaks into an adjacent literal and alignment is no longer a fake tuple: type SynInterpolatedStringPart = | String of value: string * range: range | FillExpr of fillExpr: SynExpr * formatting: SynInterpolationFormatting type SynInterpolationFormatting = | DotNet of alignment: SynExpr option * format: Ident option | Printf of specifier: string * range: range Behavioural change: plain `{x}` holes now render with invariant culture (the F# `string` operator) rather than the current thread culture, matching `string`. Adds a NativeAOT regression test under tests/AheadOfTime/NativeAOT. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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PR ready so moved to main FSharp repo