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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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Keep parens around a dangling hole with an alignment 
The old guard matched a ':fmt' qualifier only; an alignment hole was protected
by accident, because ',3' was encoded as a tuple in the fill expression and the
tuple rule kept the parens. Lifting the alignment into SynInterpolationFormatting
removed that tuple, so match the alignment here too.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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@charlesroddie @claude
charlesroddie and claude committed Jul 30, 2026
commit 930d2adc92cdab573a3f505185ba8e31b43cf571
3 changes: 3 additions & 0 deletions src/Compiler/Service/SynExpr.fs
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Expand Up @@ -1087,9 +1087,12 @@ module SynExpr =
| SynExpr.InterpolatedString _, SynExpr.Sequential _
| SynExpr.InterpolatedString _, SynExpr.Tuple(isStruct = false) -> true

// Removing the parens would let a trailing alignment or format be parsed as part of the hole,
// e.g. the ',-3' in '$"{(if b then 1 else 0),-3}"' becoming a tuple in the else branch.
| SynExpr.InterpolatedString(contents = contents), Dangling.Problematic _ ->
contents
|> List.exists (function
| SynInterpolatedStringPart.FillExpr(formatting = SynInterpolationFormatting.DotNet(alignment = Some _))
| SynInterpolatedStringPart.FillExpr(formatting = SynInterpolationFormatting.DotNet(format = Some _)) -> true
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| _ -> false)

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