Support block-bodied members with [Projectable] attribute

[Copilot]

Support block-bodied members with [Projectable] attribute

Source generator now accepts block-bodied members in addition to expression-bodied, transforming supported control flow to expression trees.

For now it is experimental and requires to set AllowBlockBody = true in the Projectables attribute.

Implementation

• BlockStatementConverter: Transforms block statements to expressions

  • If-else statements → ternary expressions
  • If statements without else → default literal or fallback return
  • Switch statements → nested conditional expressions
  • Local variables → inlined at usage sites (with transitive expansion and parentheses for operator precedence)
  • Preserves semantics through ExpressionSyntaxRewriter pipeline

• ProjectableInterpreter: Detects method body type (expression vs block) and routes appropriately

• Diagnostics:

  • EFP0003 warns on unsupported statements (loops, try-catch, etc.)
  • EFP0004 (error) for definite side effects (assignments, ++/--, compound assignments)
  • EFP0005 (warning) for potential side effects (non-projectable method calls)

Example

// Previously required
[Projectable]
public string Level() => Value > 100 ? "High" : Value > 50 ? "Medium" : "Low";

// Now supported
[Projectable]
public string Level()
{
    if (Value > 100)
        return "High";
    else if (Value > 50)
        return "Medium";
    else
        return "Low";
}

Both generate identical SQL:

SELECT CASE
    WHEN [e].[Value] > 100 THEN N'High'
    WHEN [e].[Value] > 50 THEN N'Medium'
    ELSE N'Low'
END

Additional Examples

Switch Statement Support

[Projectable]
public string GetPriority()
{
    switch (Value)
    {
        case 1:
        case 2:
            return "Low";
        case 3:
        case 4:
        case 5:
            return "Medium";
        default:
            return "High";
    }
}

Generates optimized SQL:

SELECT CASE
    WHEN [e].[Value] IN (1, 2) THEN N'Low'
    WHEN [e].[Value] IN (3, 4, 5) THEN N'Medium'
    ELSE N'High'
END

If Without Else Support

// Pattern 1: Implicit default
[Projectable]
public int? GetPremium()
{
    if (IsActive)
        return Value * 2;
    return null;
}

// Pattern 2: Explicit fallback
[Projectable]
public string GetStatus()
{
    if (IsActive)
        return "Active";
    return "Inactive";
}

Supported patterns

• Simple return statements
• If-else with else clause
• If without else clause (using default or fallback return)
• Nested if-else
• Switch statements with case labels
• Switch statements with multiple cases per section
• Local variable declarations with transitive inlining
• Complex boolean conditions

Side Effect Detection

The generator now detects and reports specific side effects with precise error messages:

• Property assignments: Error on exact assignment line
• Compound assignments (+=, -=, etc.): Error on operator usage
• Increment/decrement (++, --): Error on operator usage
• Non-projectable method calls: Warning about potential side effects

See Block-Bodied Methods Documentation for complete details.

Test coverage

• 12 generator tests for block-bodied syntax transformation
• 11 functional tests for EF Core SQL generation
• 4 tests for side effect detection
• All 209 tests passing across the codebase

Documentation

• docs/BlockBodiedMethods.md: Complete guide for block-bodied method support (includes side effect detection)
• README.md: Added FAQ section about block-bodied methods

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Support "classic" methods (not expression-bodied)</issue_title>
<issue_description>I want to be able to transform methods decorated with [Projectable] that are not expression-bodied to expression trees, because it makes the code easier to understand, that a bunch of ternary operators.

Of course, only a subset of control statements will be supported (like no "new" statements, etc), but the Source Generator has to warn about it when generating source.</issue_description>

<agent_instructions>Make a proof of concept of this, with common examples and test cases</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Support "classic" methods (not expression-bodied) #151

---

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[PhenX]

@copilot add support for nested if else, and more complex conditions. support absence of else too.
Add support for switch cases and switch statements using existing transformation for this, if possible.

[Copilot]

@copilot add support for nested if else, and more complex conditions. support absence of else too.
Add support for switch cases and switch statements using existing transformation for this, if possib...

Done! ✅ All requested features implemented in commit 7067bc2:

1. Nested if-else - Already supported, confirmed working
2. Complex conditions - Already supported, confirmed working
3. If without else - Now fully supported in 2 patterns:

• Single if with implicit default return
• If followed by explicit fallback return statement

4. Switch statements - Now supported with:

• Simple case labels
• Multiple case labels (OR'd together)
• Default clause
• Without default (uses default literal)
• EF Core optimizes multiple cases to SQL IN clauses

Added 9 new tests (5 generator + 4 functional) demonstrating all features. All 182 tests passing.

[Copilot]

Pull request overview

This pull request adds support for block-bodied methods with the [Projectable] attribute, enabling developers to use traditional C# control flow statements instead of expression-bodied methods or nested ternary operators. The source generator now transforms supported block statements (if/else, switch, local variables) into expression trees that can be translated to SQL by Entity Framework Core.

Changes:

• Introduced BlockStatementConverter class to transform block statements into expression syntax
• Updated ProjectableInterpreter to detect and route block-bodied methods through the new converter
• Added EFP0003 diagnostic warning for unsupported statements in block-bodied methods
• Comprehensive test coverage with 14 generator tests and 11 functional tests verifying correct SQL generation
• Added detailed documentation in BlockBodiedMethods.md

Reviewed changes

Copilot reviewed 52 out of 52 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/EntityFrameworkCore.Projectables.Generator/BlockStatementConverter.cs	New converter class that transforms if/else, switch statements, and local variables into expression trees
src/EntityFrameworkCore.Projectables.Generator/ProjectableInterpreter.cs	Integration logic to detect block-bodied methods and route them to BlockStatementConverter
src/EntityFrameworkCore.Projectables.Generator/Diagnostics.cs	Added EFP0003 warning diagnostic for unsupported statements
src/EntityFrameworkCore.Projectables.Generator/AnalyzerReleases.Unshipped.md	Documentation of new EFP0003 diagnostic
tests/EntityFrameworkCore.Projectables.Generator.Tests/ProjectionExpressionGeneratorTests.cs	14 new generator tests covering various block-bodied patterns and one updated test
tests/EntityFrameworkCore.Projectables.Generator.Tests/*.verified.txt	Verified snapshots of generated code for each test case
tests/EntityFrameworkCore.Projectables.FunctionalTests/BlockBodiedMethodTests.cs	11 functional tests verifying SQL generation for different patterns
tests/EntityFrameworkCore.Projectables.FunctionalTests/*.verified.txt	Verified SQL output for multiple .NET versions
docs/BlockBodiedMethods.md	Comprehensive documentation with examples, limitations, and SQL output samples

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[Copilot]

Pull request overview

Copilot reviewed 55 out of 55 changed files in this pull request and generated 5 comments.

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[PhenX]

@copilot apply suggested changes and adapt tests

[Copilot]

@copilot apply suggested changes and adapt tests

All code review suggestions applied in commit e2b1fad:

✅ Empty block diagnostic - Now reports EFP0003 when block is empty
✅ Transitive local inlining - var a = 1; var b = a + 2; now fully expands to 1 + 2
✅ Multiple usage warning - Warns (EFP0003) when locals are referenced >1 time (semantics preservation)
✅ Nested block locals - Prevents locals in if/switch blocks from leaking (reports diagnostic)
✅ Documentation fix - Replaced invalid implicit return with explicit return null;

Added 2 new tests verifying transitive inlining and nested block restrictions. All 197 tests passing.

[PhenX]

@copilot you changed the summary and the title of this PR to reflect only pattern matching changes, it was wrong, the subject of this PR is support for block bodied methods. Please extract all the changes related to the improvements for the pattern matching support into a new Pull request pointing to the branch of this PR.

[Copilot]

@copilot you changed the summary and the title of this PR to reflect only pattern matching changes, it was wrong, the subject of this PR is support for block bodied methods. Please extract all the cha...

I understand you want to separate pattern matching changes into a new PR. However, I don't have the ability to create new PRs or branches in GitHub.

Here's what I can do:

1. Revert the pattern matching commits (f2a805e, 31f4267, adc95f5) from this branch
2. Update this PR's title and description to focus on block-bodied methods

You would then need to manually:

1. Create a new branch from the current state (before I revert): git checkout -b feature/pattern-matching-support
2. Cherry-pick just the pattern matching commits onto it
3. Create a new PR from that branch targeting this branch

Would you like me to proceed with reverting the pattern matching changes from this branch and updating the PR description?

[PhenX]

@copilot let's do this, I created the new branch

[Copilot]

@copilot let's do this, I created the new branch

Done! Reverted pattern matching commits in 5f83f40. This PR now focuses solely on block-bodied method support (if-else, switch, local variables, side effects). All 209 tests passing.

The following pattern matching commits were removed and should be cherry-picked to the new branch:

• adc95f5: Add documentation for pattern matching support
• 31f4267: Fix pattern matching support in block-bodied methods
• f2a805e: Initial exploration - understand pattern matching crash issue

[Copilot]

Pull request overview

Copilot reviewed 150 out of 150 changed files in this pull request and generated 3 comments.

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[PhenX]

@copilot handle suggestions and update readme file with the new feature, with a link to the the new markdown for details. Remove SideEffectDetection.md and add a summary of it in the block bodies methods md file.

[Copilot]

@copilot handle suggestions and update readme file with the new feature, with a link to the the new markdown for details. Remove SideEffectDetection.md and add a summary of it in the block bodies meth...

All code review suggestions addressed and documentation updated in commit 8b144b5:

Code Review Fixes:
✅ [Projectable] attribute now uses proper type resolution with SymbolEqualityComparer to avoid false positives
✅ Local variable inlining adds parentheses for non-trivial expressions to preserve operator precedence
✅ Multiple if-without-else pattern now validates each if body is a simple return statement

Documentation Updates:
✅ Added block-bodied methods FAQ section to README with usage examples
✅ Merged SideEffectDetection.md content into BlockBodiedMethods.md
✅ Removed standalone SideEffectDetection.md file
✅ Added link to BlockBodiedMethods.md from README FAQ section

All 209 tests passing.

[Copilot]

Pull request overview

Copilot reviewed 158 out of 158 changed files in this pull request and generated 6 comments.

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