Add diagnostic for missing conditions for if statement

Author: kimdv

Sources/SwiftParser/Expressions.swift

@@ -2174,9 +2174,24 @@ extension Parser {
     ifHandle: RecoveryConsumptionHandle
   ) -> RawIfExprSyntax {
     let (unexpectedBeforeIfKeyword, ifKeyword) = self.eat(ifHandle)
-    // A scope encloses the condition and true branch for any variables bound
-    // by a conditional binding. The else branch does *not* see these variables.
-    let conditions = self.parseConditionList()
+
+    let conditions: RawConditionElementListSyntax
+
+    if self.at(.leftBrace) {
+      conditions = RawConditionElementListSyntax(
+        elements: [
+          RawConditionElementSyntax(
+            condition: .expression(RawExprSyntax(RawMissingExprSyntax(arena: self.arena))),
+            trailingComma: nil,
+            arena: self.arena
+          )
+        ],
+        arena: self.arena
+      )
+    } else {
+      conditions = self.parseConditionList()
+    }
+
     let body = self.parseCodeBlock(introducer: ifKeyword)
 
     // The else branch, if any, is outside of the scope of the condition.

Sources/SwiftParserDiagnostics/ParseDiagnosticsGenerator.swift

@@ -755,6 +755,18 @@ public class ParseDiagnosticsGenerator: SyntaxAnyVisitor {
     return .visitChildren
   }
 
+  public override func visit(_ node: IfExprSyntax) -> SyntaxVisitorContinueKind {
+    if shouldSkip(node) {
+      return .skipChildren
+    }
+
+    if node.conditions.count == 1, node.conditions.first?.as(ConditionElementSyntax.self)?.condition.is(MissingExprSyntax.self) == true, !node.body.leftBrace.isMissingAllTokens {
+      addDiagnostic(node.conditions, MissingConditionInStatement(firstToken: node.ifKeyword), handledNodes: [node.conditions.id])
+    }
+
+    return .visitChildren
+  }
+
   public override func visit(_ node: InitializerClauseSyntax) -> SyntaxVisitorContinueKind {
     if shouldSkip(node) {
       return .skipChildren

Sources/SwiftParserDiagnostics/ParserDiagnosticMessages.swift

@@ -333,6 +333,20 @@ public struct MissingAttributeArgument: ParserError {
   }
 }
 
+public struct MissingConditionInStatement: ParserError {
+    let firstToken: TokenSyntax
+
+    public var message: String {
+        if let name = firstToken.parent?.ancestorOrSelf(mapping: {
+            $0.nodeTypeNameForDiagnostics(allowBlockNames: false)
+        }) {
+            return "missing condition in \(name)"
+        } else {
+            return "missing condition in statement"
+        }
+    }
+}
+
 public struct MissingExpressionInStatement: ParserError {
     let firstToken: TokenSyntax
 

Tests/SwiftParserTest/translated/RecoveryTests.swift

@@ -175,26 +175,24 @@ final class RecoveryTests: XCTestCase {
   func testRecovery14() {
     assertParse(
       """
-      if {
-        }1️⃣
+      if 1️⃣{
+        }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 1: missing condition in 'if' statement
-        DiagnosticSpec(message: "expected code block in 'if' statement")
+        DiagnosticSpec(message: "missing condition in 'if' statement")
       ]
     )
   }
 
   func testRecovery15() {
     assertParse(
       """
-      if
+      if 1️⃣
         {
-        }1️⃣
+        }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 1: missing condition in 'if' statement
-        DiagnosticSpec(message: "expected code block in 'if' statement")
+        DiagnosticSpec(message: "missing condition in 'if' statement")
       ]
     )
   }
@@ -203,12 +201,11 @@ final class RecoveryTests: XCTestCase {
     assertParse(
       """
       if true {
-        } else if {
-        }1️⃣
+        } else if 1️⃣{
+        }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 2: missing condition in 'if' statement
-        DiagnosticSpec(message: "expected code block in 'if' statement")
+        DiagnosticSpec(message: "missing condition in 'if' statement")
       ]
     )
   }
@@ -218,11 +215,11 @@ final class RecoveryTests: XCTestCase {
     // body, but the error message should be sensible.
     assertParse(
       """
-      if { true } {
+      if 1️⃣{ true } {
       }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 3: missing condition in 'if' statement
+        DiagnosticSpec(message: "missing condition in 'if' statement")
         // TODO: Old parser expected error on line 3: consecutive statements on a line must be separated by ';', Fix-It replacements: 14 - 14 = ';'
         // TODO: Old parser expected error on line 3: closure expression is unused
         // TODO: Old parser expected note on line 3: did you mean to use a 'do' statement?, Fix-It replacements: 15 - 15 = 'do '
@@ -234,11 +231,11 @@ final class RecoveryTests: XCTestCase {
   func testRecovery18() {
     assertParse(
       """
-      if { true }() {
+      if 1️⃣{ true }() {
         }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 1: missing condition in 'if' statement
+        DiagnosticSpec(message: "missing condition in 'if' statement")
       ]
     )
   }
@@ -247,13 +244,12 @@ final class RecoveryTests: XCTestCase {
     assertParse(
       """
       // <rdar://problem/18940198>
-        if { { } }1️⃣
+        if 1️⃣{ { } }
       """,
       diagnostics: [
-        // TODO: Old parser expected error on line 2: missing condition in 'if' statement
+        DiagnosticSpec(message: "missing condition in 'if' statement")
         // TODO: Old parser expected error on line 2: closure expression is unused
         // TODO: Old parser expected note on line 2: did you mean to use a 'do' statement?, Fix-It replacements: 8 - 8 = 'do '
-        DiagnosticSpec(message: "expected code block in 'if' statement")
       ]
     )
   }