Change diagnostic error thrown for when string interpolations aren't closed by a parenthesis

include/swift/AST/DiagnosticsParse.def

@@ -1356,6 +1356,11 @@ ERROR(expected_type_after_as,none,
 ERROR(string_interpolation_extra,none,
       "extra tokens after interpolated string expression", ())
 
+// String interpolation isnt closed by a )
+// ie: `let west = "ye \("`
+ERROR(string_interpolation_unclosed, none,
+      "expected ')' at end of string interpolation", ())
+
 // Interpolations with parameter labels or multiple values
 WARNING(string_interpolation_list_changing,none,
       "interpolating multiple values will not form a tuple in Swift 5", ())

lib/Parse/Lexer.cpp

@@ -1884,13 +1884,23 @@ void Lexer::lexStringLiteral(unsigned CustomDelimiterLen) {
         // Successfully scanned the body of the expression literal.
         ++CurPtr;
         continue;
-      } else if ((*CurPtr == '\r' || *CurPtr == '\n') && IsMultilineString) {
-        // The only case we reach here is unterminated single line string in the
-        // interpolation. For better recovery, go on after emitting an error.
-        diagnose(CurPtr, diag::lex_unterminated_string);
-        wasErroneous = true;
-        continue;
       } else {
+        if ((*CurPtr == '\r' || *CurPtr == '\n') && IsMultilineString) {
+          diagnose(CurPtr, diag::string_interpolation_unclosed);
+          diagnose(--TmpPtr, diag::opening_paren);
+
+          // The only case we reach here is unterminated single line string in
+          // the interpolation. For better recovery, go on after emitting
+          // an error.
+          diagnose(CurPtr, diag::lex_unterminated_string);
+          wasErroneous = true;
+          continue;
+        } else if (!IsMultilineString || CurPtr == BufferEnd) {
+          diagnose(CurPtr, diag::string_interpolation_unclosed);
+          diagnose(--TmpPtr, diag::opening_paren);
+        }
+
+        // As a fallback, just emit an unterminated string error.
         diagnose(TokStart, diag::lex_unterminated_string);
         return formToken(tok::unknown, TokStart);
       }

test/Parse/multiline_errors.swift

@@ -126,14 +126,14 @@ _ = "hello\("""
             world
             """
             )!"
-            // expected-error@-4 {{unterminated string literal}}
+            // expected-error@-2 {{expected ')' at end of string interpolation}} expected-note @-4 {{to match this opening '('}}
             // expected-error@-2 {{unterminated string literal}}
 
 _ = "hello\(
             """
             world
             """)!"
-            // expected-error@-4 {{unterminated string literal}}
+            // expected-error@-4 {{expected ')' at end of string interpolation}} expected-note @-4 {{to match this opening '('}}
             // expected-error@-2 {{unterminated string literal}}
 
 _ = """
@@ -190,4 +190,5 @@ let _ = """
   \("bar
   baz
   """
-  // expected-error@-3 {{unterminated string literal}}
+  // expected-error@-3 {{expected ')' at end of string interpolation}} expected-note @-3 {{to match this opening '('}}
+  // expected-error@-4 {{unterminated string literal}}

test/Parse/string_literal_eof1.swift

@@ -1,5 +1,6 @@
 // RUN: %target-typecheck-verify-swift
 
 // NOTE: DO NOT add a newline at EOF.
-// expected-error@+1 {{unterminated string literal}}
+// expected-error@+2 {{unterminated string literal}}
+// expected-error@+1 {{expected ')' at end of string interpolation}} expected-note @+1 {{to match this opening '('}}
 _ = "foo\(

test/Parse/string_literal_eof2.swift

@@ -1,5 +1,6 @@
 // RUN: %target-typecheck-verify-swift
 
 // NOTE: DO NOT add a newline at EOF.
+// expected-error@+2 {{expected ')' at end of string interpolation}} expected-note @+2 {{to match this opening '('}}
 // expected-error@+1 {{unterminated string literal}}
 _ = "foo\("bar

test/Parse/string_literal_eof5.swift

@@ -1,7 +1,8 @@
 // RUN: %target-typecheck-verify-swift
 
 // NOTE: DO NOT add a newline at EOF.
-// expected-error@+1 {{unterminated string literal}}
+// expected-error@+2 {{unterminated string literal}}
+// expected-error@+3 {{expected ')' at end of string interpolation}} expected-note @+3 {{to match this opening '('}}
 _ = """
     foo
     \(

test/Parse/string_literal_eof6.swift

@@ -1,7 +1,8 @@
 // RUN: %target-typecheck-verify-swift
 
 // NOTE: DO NOT add a newline at EOF.
-// expected-error@+1 {{unterminated string literal}}
+// expected-error@+2 {{unterminated string literal}}
+// expected-error@+3 {{expected ')' at end of string interpolation}} expected-note @+3 {{to match this opening '('}}
 _ = """
     foo
     \("bar

test/Parse/string_literal_eof7.swift

@@ -1,7 +1,7 @@
 // RUN: %target-typecheck-verify-swift
 
-// expected-error@+4 {{unterminated string literal}}
-// expected-error@+1 {{unterminated string literal}}
+// expected-error@+4 {{expected ')' at end of string interpolation}} expected-note @+4 {{to match this opening '('}}
+// expected-error@+1 {{unterminated string literal}} expected-error@+3 {{unterminated string literal}}
 _ = """
     foo
     \("bar

test/Parse/unclosed-string-interpolation.swift

@@ -0,0 +1,27 @@
+// RUN: %target-typecheck-verify-swift
+
+let mid = "pete"
+
+_ = "mid == \(pete" 
+// expected-error @-1 {{expected ')' at end of string interpolation}} expected-note @-1 {{to match this opening '('}}
+
+let theGoat = "kanye \("
+// expected-error @-1 {{expected ')' at end of string interpolation}} expected-note @-1 {{to match this opening '('}}
+
+let equation1 = "2 + 2 = \(2 + 2" 
+// expected-error @-1 {{expected ')' at end of string interpolation}} expected-note @-1 {{to match this opening '('}}
+
+_ = """
+\(
+"""
+// expected-error @-2 {{expected ')' at end of string interpolation}} expected-note @-2 {{to match this opening '('}}
+
+let s = "\(x"; print(x) 
+// expected-error @-1 {{expected ')' at end of string interpolation}} expected-note @-1 {{to match this opening '('}}
+
+let zzz = "\(x; print(x)
+// expected-error @-1 {{expected ')' at end of string interpolation}} expected-note @-1 {{to match this opening '('}}
+
+let goatedAlbum = "The Life Of \("Pablo"
+// expected-error @-1 {{expected ')' at end of string interpolation}} expected-note @-1 {{to match this opening '('}}
+// expected-error @-1 {{unterminated string literal}}

test/expr/expressions.swift

@@ -475,9 +475,9 @@ func stringliterals(_ d: [String: Int]) {
   let x = 4
   "Hello \(x+1) world"  // expected-warning {{string literal is unused}}
 
-  "Error: \(x+1"; // expected-error {{unterminated string literal}}
+  "Error: \(x+1"; // expected-error {{expected ')' at end of string interpolation}} expected-note {{to match this opening '('}}
 
-  "Error: \(x+1   // expected-error {{unterminated string literal}}
+  "Error: \(x+1   // expected-error {{expected ')' at end of string interpolation}} expected-note {{to match this opening '('}}
   ;    // expected-error {{';' statements are not allowed}}
 
   // rdar://14050788 [DF] String Interpolations can't contain quotes
@@ -488,15 +488,16 @@ func stringliterals(_ d: [String: Int]) {
   "test \("quoted-paren (")"
   "test \("\\")"
   "test \("\n")"
-  "test \("\")" // expected-error {{unterminated string literal}}
+  "test \("\")" // expected-error {{expected ')' at end of string interpolation}} expected-note {{to match this opening '('}}
 
   "test \
   // expected-error @-1 {{unterminated string literal}} expected-error @-1 {{invalid escape sequence in literal}}
   "test \("\
-  // expected-error @-1 {{unterminated string literal}}
+  // expected-error @-1 {{expected ')' at end of string interpolation}} expected-note @-1 {{to match this opening '('}}
   "test newline \("something" +
     "something else")"
-  // expected-error @-2 {{unterminated string literal}} expected-error @-1 {{unterminated string literal}}
+  // expected-error @-2 {{expected ')' at end of string interpolation}} expected-note @-2 {{to match this opening '('}}
+  // expected-error @-2 {{unterminated string literal}}
 
   // expected-warning @+2 {{variable 'x2' was never used; consider replacing with '_' or removing it}}
   // expected-error @+1 {{unterminated string literal}}
@@ -939,10 +940,10 @@ let _ = 0xFFF_FFFF_FFFF_FFFF as Int64
 
 // rdar://problem/20289969 - string interpolation with comment containing ')' or '"'
 let _ = "foo \(42 /* ) " ) */)"
-let _ = "foo \(foo // )  " // expected-error {{unterminated string literal}}
+let _ = "foo \(foo // )  " // expected-error {{expected ')' at end of string interpolation}} expected-note {{to match this opening '('}}
 let _ = "foo \(42 /*
                    * multiline comment
                    */)end"
-// expected-error @-3 {{unterminated string literal}}
+// expected-error @-3 {{expected ')' at end of string interpolation}} expected-note @-3 {{to match this opening '('}}
 // expected-error @-2 {{expected expression}}
 // expected-error @-3 {{unterminated string literal}}