C++: better locations for bogus initializations (PR c++/88375)

PR c++/88375 reports that errors relating to invalid conversions in
initializations are reported at unhelpfully vague locations, as in
e.g.:

enum struct a : int {
  one, two
};

struct foo {
  int e1, e2;
  a e3;
} arr[] = {
  { 1, 2, a::one },
  { 3, a::two },
  { 4, 5, a::two }
};

for which g++ trunk emits the vague:

pr88375.cc:12:1: error: cannot convert 'a' to 'int' in initialization
   12 | };
      | ^

with the error at the final closing brace.

This patch uses location information for the initializers, converting the
above to:

pr88375.cc:10:11: error: cannot convert 'a' to 'int' in initialization
   10 |   { 3, a::two },
      |        ~~~^~~
      |           |
      |           a

highlighting which subexpression is problematic, and its type.

Ideally we'd also issue a note showing the field decl being initialized,
but that turned out to be more invasive.

gcc/cp/ChangeLog:
	PR c++/88375
	* typeck.c (convert_for_assignment): Capture location of rhs
	before stripping, and if available.  Use the location when
	complaining about bad conversions, labelling it with the
	rhstype if the location was present.
	* typeck2.c (digest_init_r): Capture location of init before
	stripping.

gcc/testsuite/ChangeLog:
	PR c++/88375
	* g++.dg/init/pr88375-2.C: New test.
	* g++.dg/init/pr88375.C: New test.

From-SVN: r267276

3 files changed, 73 insertions, 0 deletions

diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 4a61338..b996242 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,11 @@
 2018-12-19  David Malcolm  <dmalcolm@redhat.com>
 
+	PR c++/88375
+	* g++.dg/init/pr88375-2.C: New test.
+	* g++.dg/init/pr88375.C: New test.
+
+2018-12-19  David Malcolm  <dmalcolm@redhat.com>
+
 	* c-c++-common/Wtautological-compare-ranges.c: New test.
 	* g++.dg/cpp0x/pr51420.C: Add -fdiagnostics-show-caret and update
 	expected output.
diff --git a/gcc/testsuite/g++.dg/init/pr88375-2.C b/gcc/testsuite/g++.dg/init/pr88375-2.C
new file mode 100644
index 0000000..97ed72e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/pr88375-2.C
@@ -0,0 +1,41 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "-fdiagnostics-show-caret" }
+
+enum struct a : int {
+  one, two
+};
+
+constexpr int fn () { return 42; }
+
+struct foo {
+  int e1, e2;
+  a e3;
+} arr[] = {
+  { 3, a::two }, // { dg-error "11: cannot convert 'a' to 'int' in initialization" }
+  /* { dg-begin-multiline-output "" }
+   { 3, a::two },
+        ~~~^~~
+           |
+           a
+     { dg-end-multiline-output "" } */
+  { 6, 7, fn() }, // { dg-error "13: cannot convert 'int' to 'a' in initialization" }
+  /* { dg-begin-multiline-output "" }
+   { 6, 7, fn() },
+           ~~^~
+             |
+             int
+     { dg-end-multiline-output "" } */
+};
+
+struct bar {
+  const char *f1;
+  int f2;
+} arr_2[] = {
+  { 42 }, // { dg-error "5: invalid conversion from 'int' to 'const char\\*'" }
+  /* { dg-begin-multiline-output "" }
+   { 42 },
+     ^~
+     |
+     int
+     { dg-end-multiline-output "" } */
+};
diff --git a/gcc/testsuite/g++.dg/init/pr88375.C b/gcc/testsuite/g++.dg/init/pr88375.C
new file mode 100644
index 0000000..21dd6c1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/init/pr88375.C
@@ -0,0 +1,26 @@
+// { dg-do compile { target c++11 } }
+
+enum struct a : int {
+  one, two
+};
+
+constexpr int fn () { return 42; }
+
+struct foo {
+  int e1, e2;
+  a e3;
+} arr[] = {
+  { 1, 2, a::one },
+  { 3, a::two }, // { dg-error "11: cannot convert 'a' to 'int' in initialization" }
+  { 6, 7, 8 }, // { dg-error "11: cannot convert 'int' to 'a' in initialization" }
+  { 6, 7, fn() }, // { dg-error "13: cannot convert 'int' to 'a' in initialization" }
+};
+
+struct bar {
+  const char *f1;
+  int f2;
+} arr_2[] = {
+  { "hello world", 42 },
+  { 42 }, // { dg-error "5: invalid conversion from 'int' to 'const char\\*'" }
+  { "hello", "world" }, // { dg-error "14: invalid conversion from 'const char\\*' to 'int'" }
+};