Use at(prefix:) when consuming generic arguments

Author: Azoy

Sources/SwiftParser/Names.swift

@@ -193,7 +193,7 @@ extension Parser {
 
     let (unexpectedBeforeName, name) = self.expect(anyIn: IdentifierTypeSyntax.NameOptions.self, default: .identifier)
     let generics: RawGenericArgumentClauseSyntax?
-    if self.atContextualPunctuator("<") {
+    if self.at(prefix: "<") {
       generics = self.parseGenericArguments()
     } else {
       generics = nil
@@ -229,7 +229,7 @@ extension Parser {
         default: .identifier
       )
       let generics: RawGenericArgumentClauseSyntax?
-      if self.atContextualPunctuator("<") {
+      if self.at(prefix: "<") {
         generics = self.parseGenericArguments()
       } else {
         generics = nil

Sources/SwiftParser/Types.swift

@@ -295,7 +295,7 @@ extension Parser {
             name = missingToken(.identifier)
           }
           let generics: RawGenericArgumentClauseSyntax?
-          if self.atContextualPunctuator("<") {
+          if self.at(prefix: "<") {
             generics = self.parseGenericArguments()
           } else {
             generics = nil
@@ -702,15 +702,6 @@ extension Parser.Lookahead {
         fallthrough
       }
 
-      // '-123' for value generics.
-      if self.currentToken.tokenText == "-",
-        self.peek(isAt: .integerLiteral)
-      {
-        self.consumeAnyToken()
-        self.consumeAnyToken()
-        return true
-      }
-
       return false
     case TokenSpec(.Self), TokenSpec(.identifier):
       guard self.canParseTypeIdentifier() else {
@@ -861,7 +852,7 @@ extension Parser.Lookahead {
   }
 
   mutating func canParseAsGenericArgumentList() -> Bool {
-    guard self.atContextualPunctuator("<") else {
+    guard self.at(prefix: "<") else {
       return false
     }
 
@@ -881,9 +872,21 @@ extension Parser.Lookahead {
     if !self.at(prefix: ">") {
       var loopProgress = LoopProgressCondition()
       repeat {
-        guard self.canParseType() else {
-          return false
+        // A generic argument can either be a type or an integer literal (who is
+        // optionally negative).
+        if self.canParseType() {
+          continue
+        } else if self.currentToken.tokenText == "-",
+          self.peek(isAt: .integerLiteral)
+        {
+          self.consumeAnyToken()
+          self.consumeAnyToken()
+          continue
+        } else if self.consume(if: .integerLiteral) != nil {
+          continue
         }
+        
+        return false
         // Parse the comma, if the list continues.
       } while self.consume(if: .comma) != nil && self.hasProgressed(&loopProgress)
     }

Tests/SwiftParserTest/ValueGenericsTests.swift

@@ -139,7 +139,49 @@ final class ValueGenericsTests: ParserTestCase {
       """,
       experimentalFeatures: .valueGenerics
     )
+    
+    assertParse(
+      """
+      let x = Generic<123>.self
+      """,
+      experimentalFeatures: .valueGenerics
+    )
+
+    assertParse(
+      """
+      let x = Generic<-123>.self
+      """,
+      experimentalFeatures: .valueGenerics
+    )
+
+    assertParse(
+      """
+      let x = Generic<123, Int>.self
+      """,
+      experimentalFeatures: .valueGenerics
+    )
+
+    assertParse(
+      """
+      let x = Generic<-123, Int>.self
+      """,
+      experimentalFeatures: .valueGenerics
+    )
+    
+    assertParse(
+      """
+      let x = Generic<Int, 123>.self
+      """,
+      experimentalFeatures: .valueGenerics
+    )
 
+    assertParse(
+      """
+      let x: Generic<Int, -123>.self
+      """,
+      experimentalFeatures: .valueGenerics
+    )
+    
     assertParse(
       """
       typealias One = 1️⃣1
@@ -251,5 +293,18 @@ final class ValueGenericsTests: ParserTestCase {
       ],
       experimentalFeatures: .valueGenerics
     )
+    
+    assertParse(
+      "func foo() -> (1️⃣-1) X",
+      diagnostics: [
+        DiagnosticSpec(
+          message: "expected type in tuple type",
+          fixIts: ["insert type"]
+        ),
+        DiagnosticSpec(message: "unexpected code '-1' in tuple type"),
+      ],
+      fixedSource: "func foo() -> (<#type#>-1) X",
+      experimentalFeatures: [.valueGenerics]
+    )
   }
 }