* Preserve the more restrictive syntax for typed patterns in the language specification

* Make the parser's warning a migration warning

Author: prolativ

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2821,14 +2821,25 @@ object Parsers {
       if (isIdent(nme.raw.BAR)) { in.nextToken(); pattern1(location) :: patternAlts(location) }
       else Nil
 
-    /**  Pattern1     ::= Pattern2 [Ascription]
+    /**  Pattern1     ::= PatVar Ascription
+     *                  | [‘-’] integerLiteral Ascription
+     *                  | [‘-’] floatingPointLiteral Ascription
+     *                  | Pattern2
      */
     def pattern1(location: Location = Location.InPattern): Tree =
       val p = pattern2()
       if in.isColon then
         val isVariableOrNumber = isVarPattern(p) || p.isInstanceOf[Number]
         if !isVariableOrNumber then
-          warning(em"Only variable and number literal patterns can have type ascriptions")
+          report.gradualErrorOrMigrationWarning(
+            em"""Type ascriptions after patterns other than:
+                |  * variable pattern, e.g. `case x: String =>`
+                |  * number literal pattern, e.g. `case 10.5: Double =>`
+                |are no longer supported. Remove the type ascription or move it to a separate variable pattern.""",
+            in.sourcePos(),
+            warnFrom = `3.3`,
+            errorFrom = future
+          )
         in.nextToken()
         ascription(p, location)
       else p

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -188,6 +188,7 @@ class CompilationTests {
       compileFile("tests/neg-custom-args/i13026.scala", defaultOptions.and("-print-lines")),
       compileFile("tests/neg-custom-args/i13838.scala", defaultOptions.and("-Ximplicit-search-limit", "1000")),
       compileFile("tests/neg-custom-args/jdk-9-app.scala", defaultOptions.and("-release:8")),
+      compileFile("tests/neg-custom-args/i10994.scala", defaultOptions.and("-source", "future")),
     ).checkExpectedErrors()
   }
 

docs/_docs/internals/syntax.md

@@ -319,7 +319,10 @@ TypeCaseClauses   ::=  TypeCaseClause { TypeCaseClause }
 TypeCaseClause    ::=  ‘case’ (InfixType | ‘_’) ‘=>’ Type [semi]
 
 Pattern           ::=  Pattern1 { ‘|’ Pattern1 }                                Alternative(pats)
-Pattern1          ::=  Pattern2 [‘:’ RefinedType]                               Bind(name, Typed(Ident(wildcard), tpe))
+Pattern1          ::=  PatVar ‘:’ RefinedType                                   Bind(name, Typed(Ident(wildcard), tpe))
+                    |  [‘-’] integerLiteral ‘:’ RefinedType                     Typed(pat, tpe)
+                    |  [‘-’] floatingPointLiteral ‘:’ RefinedType               Typed(pat, tpe)
+                    |  Pattern2
 Pattern2          ::=  [id ‘@’] InfixPattern [‘*’]                              Bind(name, pat)
 InfixPattern      ::=  SimplePattern { id [nl] SimplePattern }                  InfixOp(pat, op, pat)
 SimplePattern     ::=  PatVar                                                   Ident(wildcard)

docs/_docs/reference/syntax.md

@@ -312,7 +312,10 @@ TypeCaseClauses   ::=  TypeCaseClause { TypeCaseClause }
 TypeCaseClause    ::=  ‘case’ (InfixType | ‘_’) ‘=>’ Type [semi]
 
 Pattern           ::=  Pattern1 { ‘|’ Pattern1 }
-Pattern1          ::=  Pattern2 [‘:’ RefinedType]
+Pattern1          ::=  PatVar ‘:’ RefinedType
+                    |  [‘-’] integerLiteral ‘:’ RefinedType
+                    |  [‘-’] floatingPointLiteral ‘:’ RefinedType
+                    |  Pattern2
 Pattern2          ::=  [id ‘@’] InfixPattern [‘*’]
 InfixPattern      ::=  SimplePattern { id [nl] SimplePattern }
 SimplePattern     ::=  PatVar

tests/neg-custom-args/i10994.check

@@ -0,0 +1,7 @@
+-- Error: tests/neg-custom-args/i10994.scala:2:19 ----------------------------------------------------------------------
+2 |  case (b: Boolean): Boolean => () // error
+  |                   ^
+  |                   Type ascriptions after patterns other than:
+  |                     * variable pattern, e.g. `case x: String =>`
+  |                     * number literal pattern, e.g. `case 10.5: Double =>`
+  |                   are no longer supported. Remove the type ascription or move it to a separate variable pattern.

tests/neg-custom-args/i10994.scala

@@ -0,0 +1,2 @@
+def foo = true match
+  case (b: Boolean): Boolean => () // error

tests/neg/t5702-neg-bad-and-wild.check

@@ -59,7 +59,10 @@
 -- Warning: tests/neg/t5702-neg-bad-and-wild.scala:13:22 ---------------------------------------------------------------
 13 |      case List(1, _*3:) =>  // error // error
    |                      ^
-   |                      Only variable and number literal patterns can have type ascriptions
+   |                  Type ascriptions after patterns other than:
+   |                    * variable pattern, e.g. `case x: String =>`
+   |                    * number literal pattern, e.g. `case 10.5: Double =>`
+   |                  are no longer supported. Remove the type ascription or move it to a separate variable pattern.
 -- Warning: tests/neg/t5702-neg-bad-and-wild.scala:22:20 ---------------------------------------------------------------
 22 |    val K(x @ _*) = k
    |                    ^

tests/pos/i10994.scala

@@ -1,2 +1,2 @@
 def foo = true match
-  case (b: Boolean): Boolean => ()
+  case (b: Boolean): Boolean => () // warning