[Diagnostics] Add a fix-it for try instead of throws in function decl… (#27647)

* [Diagnostics] Add a fix-it for try instead of throws in function decls and types.

Sometimes one would misstype `throws` for `try` so we provide a fix-it for that.
It might happen in two cases:

In function declarations:
```swift
func foo() try {}
```

In function types:
```swift
let f = () try -> Int
```

Resolves SR-11574.

Author: vguerra

lib/Parse/ParsePattern.cpp

@@ -782,7 +782,7 @@ Parser::parseFunctionSignature(Identifier SimpleName,
   } else if (Tok.is(tok::kw_rethrows)) {
     throwsLoc = consumeToken();
     rethrows = true;
-  } else if (Tok.is(tok::kw_throw)) {
+  } else if (Tok.isAny(tok::kw_throw, tok::kw_try)) {
     throwsLoc = consumeToken();
     diagnose(throwsLoc, diag::throw_in_function_type)
       .fixItReplace(throwsLoc, "throws");

lib/Parse/ParseType.cpp

@@ -399,11 +399,11 @@ ParserResult<TypeRepr> Parser::parseType(Diag<> MessageID,
   // Don't consume 'throws', if the next token is not '->', so we can emit a
   // more useful diagnostic when parsing a function decl.
   SourceLoc throwsLoc;
-  if (Tok.isAny(tok::kw_throws, tok::kw_rethrows, tok::kw_throw) &&
+  if (Tok.isAny(tok::kw_throws, tok::kw_rethrows, tok::kw_throw, tok::kw_try) &&
       peekToken().is(tok::arrow)) {
     if (Tok.isNot(tok::kw_throws)) {
       // 'rethrows' is only allowed on function declarations for now.
-      // 'throw' is probably a typo for 'throws'.
+      // 'throw' or 'try' are probably typos for 'throws'.
       Diag<> DiagID = Tok.is(tok::kw_rethrows) ?
         diag::rethrowing_function_type : diag::throw_in_function_type;
       diagnose(Tok.getLoc(), DiagID)

test/Parse/errors.swift

@@ -127,3 +127,9 @@ func fixitThrow2() throws {
 }
 
 let fn: () -> throws Void  // expected-error{{'throws' may only occur before '->'}} {{12-12=throws }} {{15-22=}}
+
+// SR-11574
+func fixitTry0<T>(a: T) try where T:ExpressibleByStringLiteral {} // expected-error{{expected throwing specifier; did you mean 'throws'?}} {{25-28=throws}}
+func fixitTry1<T>(a: T) try {} // expected-error{{expected throwing specifier; did you mean 'throws'?}} {{25-28=throws}}
+func fixitTry2() try {} // expected-error{{expected throwing specifier; did you mean 'throws'?}} {{18-21=throws}}
+let fixitTry3 : () try -> Int // expected-error{{expected throwing specifier; did you mean 'throws'?}} {{20-23=throws}}