Avoid disambiguating parentheses being removed from called closures in conditions (#298)

A bit of a mouthfull to fit into a reasonably sized commit message. The
NoParensAroundConditions rule removed parens around immediately called closures
and in doing so introduced ambiguities into code that was correct to begin with.

Author: stackotter

Sources/SwiftFormatRules/NoParensAroundConditions.swift

@@ -30,10 +30,16 @@ public final class NoParensAroundConditions: SyntaxFormatRule {
     assert(tuple.elementList.count == 1)
     let expr = tuple.elementList.first!.expression
 
-    // If the condition is a function with a trailing closure, removing the
-    // outer set of parentheses introduces a parse ambiguity.
-    if let fnCall = expr.as(FunctionCallExprSyntax.self), fnCall.trailingClosure != nil {
-      return ExprSyntax(tuple)
+    // If the condition is a function with a trailing closure or if it's an immediately called
+    // closure, removing the outer set of parentheses introduces a parse ambiguity.
+    if let fnCall = expr.as(FunctionCallExprSyntax.self) {
+      if fnCall.trailingClosure != nil {
+        // Leave parentheses around call with trailing closure.
+        return ExprSyntax(tuple)
+      } else if fnCall.calledExpression.as(ClosureExprSyntax.self) != nil {
+        // Leave parentheses around immediately called closure.
+        return ExprSyntax(tuple)
+      }
     }
 
     diagnose(.removeParensAroundExpression, on: expr)

Tests/SwiftFormatRulesTests/NoParensAroundConditionsTests.swift

@@ -160,4 +160,17 @@ final class NoParensAroundConditionsTests: LintOrFormatRuleTestCase {
                 }
                 """)
   }
+
+  func testParensAroundAmbiguousConditions() {
+    XCTAssertFormatting(
+      NoParensAroundConditions.self,
+      input: """
+             if ({ true }()) {}
+             if (functionWithTrailingClosure { 5 }) {}
+             """,
+      expected: """
+                if ({ true }()) {}
+                if (functionWithTrailingClosure { 5 }) {}
+                """)
+  }
 }