Restructure invalid parameter diagnostic

Diagnose the fact that we're missing a colon, not the fact that we're missing a type since that's actually what has gone wrong.

Author: CodaFi

include/swift/AST/DiagnosticsParse.def

@@ -870,8 +870,6 @@ ERROR(expected_parameter_colon,PointsToFirstBadToken,
       "expected ':' following argument label and parameter name", ())
 ERROR(expected_assignment_instead_of_comparison_operator,none,
       "expected '=' instead of '==' to assign default value for parameter", ())
-ERROR(missing_parameter_type,PointsToFirstBadToken,
-      "parameter requires an explicit type", ())
 ERROR(multiple_parameter_ellipsis,none,
       "only a single variadic parameter '...' is permitted", ())
 ERROR(parameter_vararg_default,none,

lib/Parse/ParsePattern.cpp

@@ -327,6 +327,9 @@ Parser::parseParameterClause(SourceLoc &leftParenLoc,
         // was invalid.  Remember that.
         if (type.isParseError() && !type.hasCodeCompletion())
           param.isInvalid = true;
+      } else if (paramContext != Parser::ParameterContextKind::Closure) {
+        diagnose(Tok, diag::expected_parameter_colon);
+        param.isInvalid = true;
       }
     } else {
       // Otherwise, we have invalid code.  Check to see if this looks like a
@@ -516,13 +519,6 @@ mapParsedParameters(Parser &parser,
         // or typealias with underlying function type.
         param->setAutoClosure(attrs.has(TypeAttrKind::TAK_autoclosure));
       }
-    } else if (paramContext != Parser::ParameterContextKind::Closure) {
-      // Non-closure parameters require a type.
-      if (!param->isInvalid())
-        parser.diagnose(param->getLoc(), diag::missing_parameter_type);
-
-      param->setSpecifier(ParamSpecifier::Default);
-      setInvalid();
     } else if (paramInfo.SpecifierLoc.isValid()) {
       StringRef specifier;
       switch (paramInfo.SpecifierKind) {

test/Parse/invalid.swift

@@ -76,7 +76,7 @@ protocol Animal<Food> {  // expected-error {{protocols do not allow generic para
 // SR-573 - Crash with invalid parameter declaration
 class Starfish {}
 struct Salmon {}
-func f573(s Starfish,  // expected-error {{parameter requires an explicit type}}
+func f573(s Starfish,  // expected-error {{expected ':' following argument label and parameter name}}
           _ ss: Salmon) -> [Int] {}
 func g573() { f573(Starfish(), Salmon()) }
 
@@ -89,7 +89,7 @@ func SR979b(inout inout b: Int) {} // expected-error {{inout' before a parameter
 // expected-error@-1 {{parameter must not have multiple '__owned', 'inout', or '__shared' specifiers}} {{19-25=}}
 func SR979d(let let a: Int) {} // expected-warning {{'let' in this position is interpreted as an argument label}} {{13-16=`let`}}
 // expected-error @-1 {{expected ',' separator}} {{20-20=,}} 
-// expected-error @-2 {{parameter requires an explicit type}}
+// expected-error @-2 {{expected ':' following argument label and parameter name}}
 // expected-warning @-3 {{extraneous duplicate parameter name; 'let' already has an argument label}} {{13-17=}}
 func SR979e(inout x: inout String) {} // expected-error {{parameter must not have multiple '__owned', 'inout', or '__shared' specifiers}} {{13-18=}}
 func SR979g(inout i: inout Int) {} // expected-error {{parameter must not have multiple '__owned', 'inout', or '__shared' specifiers}} {{13-18=}}

test/Sema/immutability.swift

@@ -370,7 +370,7 @@ func testSelectorStyleArguments1(_ x: Int, bar y: Int) {
 func testSelectorStyleArguments2(let x: Int, // expected-warning {{'let' in this position is interpreted as an argument label}}{{34-37=`let`}}
                                  let bar y: Int) { // expected-warning {{'let' in this position is interpreted as an argument label}}{{34-37=`let`}}
 // expected-error @-1 {{expected ',' separator}}
-// expected-error @-2 {{parameter requires an explicit type}}
+// expected-error @-2 {{expected ':' following argument label and parameter name}}
 }
 func testSelectorStyleArguments3(_ x: Int, bar y: Int) {
   ++x  // expected-error {{cannot pass immutable value to mutating operator: 'x' is a 'let' constant}}