Convert float/double += 1 into increment and decrement expressions - #3933
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Updates increment/decrement detection in the C# decompiler so float/double pre-increment/decrement can round-trip as ++x/--x (instead of x += 1f), and expands the pretty-printing fixture coverage for floating-point and decimal compound assignments.
Changes:
- Extend
PrettifyAssignmentsincrement/decrement detection to accept constant-1operands forfloatanddouble. - Revive/expand
CompoundAssignmentTestfixtures with extensivefloat/double/decimalcompound-assignment and inc/dec scenarios.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.
| File | Description |
|---|---|
| ICSharpCode.Decompiler/CSharp/Transforms/PrettifyAssignments.cs | Broadens ++/-- detection from integer-only constants to also cover float/double constant-1 cases. |
| ICSharpCode.Decompiler.Tests/TestCases/Pretty/CompoundAssignmentTest.cs | Adds large fixture coverage for compound assignments and inc/dec over float, double, and decimal across many receiver shapes. |
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Reviving the 2020 test-cases-fp-types fixtures (compound assignment on float, double and decimal) exposed an asymmetry: post-increment and post-decrement on float/double round-tripped as x++/x--, but the pre forms came back as x += 1f because the increment detection in PrettifyAssignments only accepted integer constants. C# defines ++/-- on floating-point types as adding or subtracting exactly 1, so the conversion is exact for a constant 1 operand. Decimal already works through the op_Increment/op_Decrement path. Assisted-by: Claude:claude-fable-5:Claude Code
Operator precedence made the condition read (setting && Add) || Subtract, so 'x -= 1' was converted to 'x--' even with IntroduceIncrementAndDecrement disabled. Only observable with the non-default setting, which no fixture configuration exercises, so no test accompanies the fix. Assisted-by: Claude:claude-fable-5:Claude Code
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Aug 3, 2026
decimal has no IL literal: legacy csc compiles 0m to a Decimal.Zero field load, which already decompiled to the literal, but Roslyn compiles it to a zero-initialization, which decompiled to default(decimal). The two forms are bit-identical for decimal, so the literal is no less faithful to the IL and matches what a human writes; it also removes the per-compiler split in the CompoundAssignmentTest fixture. Assisted-by: Claude:claude-fable-5:Claude Code
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Revives the 2020
test-cases-fp-typesfixture work: ~770 lines of compound-assignment / increment / decrement coverage forfloat,double, anddecimalinCompoundAssignmentTest.cs, mirroring the existing integer sections (fields, properties, params, locals, ref returns, custom-struct receivers).The revived fixtures exposed an asymmetry: post-increment/decrement on float/double round-tripped as
x++/x--, but the pre forms decompiled tox += 1f, because the increment detection inPrettifyAssignmentsonly accepted integer constants. Since C# defines++/--on floating-point types as adding/subtracting exactly 1, a constant-1 float/double operand now also converts. Decimal needed no change (op_Increment/op_Decrementpath).Verified:
CompoundAssignmentTestgreen in all 24 configs, full decompiler suite green on Linux (3082 passed / 0 failed / 44 skipped).🤖 Generated with Claude Code