Add support for shortened switch

changelog/dmd.shortened-switch.dd

@@ -0,0 +1,30 @@
+Add a shortened form for switch's case expression using `=>` instead of `:` to make `break` optional, it'll automatically break at the end of the scope.
+
+---
+enum K = 42;
+switch (K)
+{
+    case 42 => printf("yes!\n");
+
+    default => printf("no!\n");
+}
+---
+
+Is equivalent to:
+
+---
+enum K = 42;
+switch (42)
+{
+    case 42:
+    {
+        printf("yes!\n");
+        break;
+    }
+    default:
+    {
+        printf("no!\n");
+        break;
+    }
+}
+---

compiler/src/dmd/parse.d

@@ -6419,7 +6419,14 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
                     nextToken(); //comma
                 }
                 while (token.value != TOK.colon && token.value != TOK.endOfFile);
-                check(TOK.colon);
+
+                bool insertBreak = false;
+                if (token.value == TOK.goesTo) {
+                    insertBreak = true;
+                    nextToken();
+                }
+                else
+                    check(TOK.colon);
 
                 /* case exp: .. case last:
                  */
@@ -6449,6 +6456,8 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
                         if (cur && cur.isBreakStatement())
                             break;
                     }
+                    if (insertBreak)
+                        statements.push(new AST.BreakStatement(loc, null));
                     s = new AST.CompoundStatement(loc, statements);
                 }
                 else
@@ -6475,7 +6484,13 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
         case TOK.default_:
             {
                 nextToken();
-                check(TOK.colon);
+                bool insertBreak = false;
+                if (token.value == TOK.goesTo) {
+                    insertBreak = true;
+                    nextToken();
+                }
+                else
+                    check(TOK.colon);
 
                 if (flags & ParseStatementFlags.curlyScope)
                 {
@@ -6484,6 +6499,8 @@ class Parser(AST, Lexer = dmd.lexer.Lexer) : Lexer
                     {
                         statements.push(parseStatement(ParseStatementFlags.curlyScope));
                     }
+                    if (insertBreak)
+                        statements.push(new AST.BreakStatement(loc, null));
                     s = new AST.CompoundStatement(loc, statements);
                 }
                 else

compiler/test/runnable/switch.d

@@ -0,0 +1,124 @@
+/*
+RUN_OUTPUT:
+---
+A: yes
+B: yes
+C: yes
+---
+*/
+
+// main.d -------------------------------------------------------
+
+import core.stdc.stdio: printf;
+
+void simple()
+{
+    enum K = 42;
+    switch (K)
+    {
+        case 0 => printf("A: no0\n");
+        case 42 => printf("A: yes\n");
+        case 1 => printf("A: no1\n");
+
+        default => printf("A: default\n");
+    }
+    switch (K)
+    {
+        case 0 => {
+            printf("B: no0\n");
+        }
+        case 42 => {
+            printf("B: yes\n");
+        }
+        case 1 => {
+            printf("B: no1\n");
+        }
+
+        default => {
+            printf("B: default\n");
+        }
+    }
+    switch (K)
+    {
+        case 0: printf("C: no0\n"); break;
+        case 42: printf("C: yes\n"); break;
+        case 1: printf("C: no1\n"); break;
+
+        default: printf("C: default\n");
+    }
+}
+
+
+void send_1(short* to, short* from, int count)
+{
+    auto n = (count + 7) / 8;
+    switch (count % 8) {
+    case 0: do { *to++ = *from++;
+                 goto case;
+    case 7:      *to++ = *from++;
+                 goto case;
+    case 6:      *to++ = *from++;
+                 goto case;
+    case 5:      *to++ = *from++;
+                 goto case;
+    case 4:      *to++ = *from++;
+                 goto case;
+    case 3:      *to++ = *from++;
+                 goto case;
+    case 2:      *to++ = *from++;
+                 goto case;
+    case 1:      *to++ = *from++;
+                 continue;
+            } while (--n > 0);
+            break;
+    default: break;
+    }
+}
+
+void send_2(short* to, short* from, int count)
+{
+    auto n = (count + 7) / 8;
+    switch (count % 8) {
+    case 0 => do { *to++ = *from++;
+                 goto case;
+    case 7 =>      *to++ = *from++;
+                 goto case;
+    case 6 =>      *to++ = *from++;
+                 goto case;
+    case 5 =>      *to++ = *from++;
+                 goto case;
+    case 4 =>      *to++ = *from++;
+                 goto case;
+    case 3 =>      *to++ = *from++;
+                 goto case;
+    case 2 =>      *to++ = *from++;
+                 goto case;
+    case 1 =>      *to++ = *from++;
+                 continue;
+            } while (--n > 0);
+            break;
+    default: break;
+    }
+}
+
+void duff_device()
+{
+    {
+        short[4] data = [1,2,3,4];
+        short[4] output = 0;
+        send_1(output.ptr, data.ptr, cast(int) data.length);
+        assert(output[0] == 1 && output[1] == 2 && output[2] == 3 && output[3] == 4);
+    }
+    {
+        short[4] data = [1,2,3,4];
+        short[4] output = 0;
+        send_2(output.ptr, data.ptr, cast(int) data.length);
+        assert(output[0] == 1 && output[1] == 2 && output[2] == 3 && output[3] == 4);
+    }
+}
+
+void main()
+{
+    simple();
+    duff_device();
+}