[clang] [C2y] Add test coverage for WG14 N3370 (PR #115054)

[Erich Keane via cfe-commits]

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+// RUN: %clang_cc1 -verify=expected,c-expected -std=c2y -Wall -pedantic %s
+// RUN: %clang_cc1 -verify=expected,c-expected,ped -std=c23 -Wall -pedantic %s
+// RUN: %clang_cc1 -verify=expected,cxx-expected,gnu -Wall -pedantic -x c++ %s
+// RUN: %clang_cc1 -verify=expected,c-expected,pre -std=c2y -Wpre-c2y-compat -Wall -pedantic %s
+
+/* WG14 N3370: Yes
+ * Case range expressions v3.1
+ *
+ * This introduces the ability to specify closed ranges in case statements in a
+ * switch statement. This was already a well-supported Clang extension before
+ * it was standardized.
+ */
+
+void correct(int i) {
+  constexpr int j = 100, k = 200;
+  switch (i) {
+  case 12 ... 14: break; /* gnu-warning {{case ranges are a GNU extension}}
+                            ped-warning {{case ranges are a C2y extension}}
+                            pre-warning {{case ranges are incompatible with C standards before C2y}}
+                          */
+  // Implementations are encouraged to diagnose empty ranges.
+  case 15 ... 11: break;  /* expected-warning {{empty case range specified}}
+                             gnu-warning {{case ranges are a GNU extension}}
+                             ped-warning {{case ranges are a C2y extension}}
+                             pre-warning {{case ranges are incompatible with C standards before C2y}}
+                           */
+  // This is not an empty range, it's a range of a single value.
+  case 10 ... 10: break; /* gnu-warning {{case ranges are a GNU extension}}
+                            ped-warning {{case ranges are a C2y extension}}
+                            pre-warning {{case ranges are incompatible with C standards before C2y}}
+                          */
+  case j ... k: break;   /* gnu-warning {{case ranges are a GNU extension}}
+                            ped-warning {{case ranges are a C2y extension}}
+                            pre-warning {{case ranges are incompatible with C standards before C2y}}
+                          */
+  }
+}
+
+void incorrect(int i) { // cxx-expected-note 2 {{declared here}}
+  switch (i) {
+  // The values have to be integer constant expressions. Note that when the
+  // initial value in the range is an error, we don't issue the warnings about
+  // extensions or incompatibility.
+  case i ... 10: break;    /* c-expected-error {{expression is not an integer constant expression}}
+                              cxx-expected-error {{case value is not a constant expression}}
+                              cxx-expected-note {{function parameter 'i' with unknown value cannot be used in a constant expression}}
+                            */
+  case 10 ... i: break;    /* c-expected-error {{expression is not an integer constant expression}}
+                              cxx-expected-error {{case value is not a constant expression}}
+                              cxx-expected-note {{function parameter 'i' with unknown value cannot be used in a constant expression}}
+                              gnu-warning {{case ranges are a GNU extension}}
+                              ped-warning {{case ranges are a C2y extension}}
+                              pre-warning {{case ranges are incompatible with C standards before C2y}}
+                            */
+  case 1.3f ... 10: break; /* c-expected-error {{integer constant expression must have integer type, not 'float'}}
+                              cxx-expected-error {{conversion from 'float' to 'int' is not allowed in a converted constant expression}}
+                            */
+  case 10 ... "a": break;  /* c-expected-error {{integer constant expression must have integer type, not 'char[2]'}}
+                              cxx-expected-error {{value of type 'const char[2]' is not implicitly convertible to 'int'}}
+                              gnu-warning {{case ranges are a GNU extension}}
+                              ped-warning {{case ranges are a C2y extension}}
+                              pre-warning {{case ranges are incompatible with C standards before C2y}}
+                            */
+  }
+
+  switch (i) {
+  // Cannot have multiple cases covering the same value.
+  // FIXME: diagnostic quality here is poor. The "previous case" note is
+  // showing up on a subsequent line (I'd expect the error and note to be
+  // reversed), and "duplicate case value 20" is showing up on a line where
+  // there is no duplicate value 20 to begin with.
+  case 10 ... 20: break; /* expected-error {{duplicate case value '11'}}
+                            expected-note {{previous case defined here}}
+                            gnu-warning {{case ranges are a GNU extension}}
+                            ped-warning {{case ranges are a C2y extension}}
+                            pre-warning {{case ranges are incompatible with C standards before C2y}}
+                          */
+  case 11: break;        /* expected-note {{previous case defined here}}
+                          */
+  case 11 ... 14: break; /* expected-error {{duplicate case value '20'}}
----------------
erichkeane wrote:

Oh my :) 

https://github.com/llvm/llvm-project/pull/115054