C#: Fix AutoFormat not inserting newlines in synthesized nodes#7189
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knutwannheden merged 3 commits intomainfrom Mar 28, 2026
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Roslyn's Formatter.Format has a SuppressWrappingIfOnSingleLine heuristic
that preserves single-line formatting when all tokens are on one line.
This meant synthesized nodes with Space.Empty (produced by templates or
manual AST construction) stayed compressed on one line after formatting.
Fix: set WrappingPreserveSingleLine and WrappingKeepStatementsOnSingleLine
to false in the Roslyn options, so the formatter inserts structural newlines
(after {, before }, before else, etc.) even when the input has none.
…ement templates - AutoFormatManualIfElseWithMaybeAutoFormatAtBlockLevel: reproduces the AvoidNestingTernary pattern (manual AST construction with Space.Empty, conditions extracted from ternary, MaybeAutoFormat at Block level) - AutoFormatSplicedMultiStatementTemplate: multi-statement template that produces a SyntheticBlock, flattened and individually formatted - AutoFormatSplicedSubtreePreservesSurroundingCode: formatting quirks in surrounding code are preserved when only the spliced subtree is formatted - Rename RoslynFormatterNormalizesWhitespace to reflect new behavior
knutwannheden
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autoformat-should-handle-synthesized-nodes-with-space.empty
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Motivation
When a recipe constructs AST nodes with
Space.Empty(e.g., building an if/else chain from scratch, or usingCSharpTemplatewith compressed formatting),AutoFormatproduces single-line output likeif (a) { s = "A"; } else { s = "D"; }instead of properly formatted multi-line code.The root cause is Roslyn's
Formatter.Formathas aSuppressWrappingIfOnSingleLineheuristic that preserves single-line formatting when all tokens are on one line. Since synthesized nodes withSpace.Emptyprint without newlines, Roslyn sees "everything is on one line" and adds spaces but never inserts structural newlines.Summary
CSharpFormattingOptions.WrappingPreserveSingleLineandWrappingKeepStatementsOnSingleLinetofalseinFormatWithRoslyn, disabling the single-line preservation heuristic so Roslyn inserts structural newlines (after{, before}, beforeelse, etc.)BuildOptionshelper inRoslynFormatterto centralize Roslyn option configurationRewriteRunintegration tests:AvoidNestingTernarypattern (with surrounding formatting quirks preserved)SyntheticBlockthat gets flattened and individually formattedTest plan
AvoidNestingTernarytests in recipes-csharp (branchquiet-badger) pass — 5/5