Add Rust support to source highlighting

[ Backport of master commit d806ea2d0e. ]

Currently, no release of GNU Source Highlight supports Rust.  However,
I've checked in a patch to do so there, and I plan to make a new
release sometime this summer.

This patch prepares gdb for that by adding support for Rust to the
source highlighting code.

Because Source Highlight will throw an exception if the language is
unrecognized, this also changes gdb to ignore exceptions here.  This
will cause gdb to fall back to un-highlighted source text.

This updates gdb's configure script to reject the combination of
Source Highlight and -static-libstdc++.  This is done because it's not
possible to use -static-libstdc++ and then catch exceptions from a
shared library.

Tested with the current and development versions of Source Highlight.

gdb/ChangeLog
2019-08-19  Tom Tromey  <tom@tromey.com>

	* configure: Rebuild.
	* configure.ac: Disallow the combination of -static-libstdc++ and
	source highlight.
	* source-cache.c (get_language_name): Handle rust.
	(source_cache::get_source_lines): Ignore highlighting exceptions.

---
 gdb/ChangeLog      |  8 ++++++++
 gdb/configure      |  6 ++++++
 gdb/configure.ac   |  8 ++++++++
 gdb/source-cache.c | 33 ++++++++++++++++++++++-----------
 4 files changed, 44 insertions(+), 11 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index fd3a86cbcf..76fcda3ba7 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2019-08-19  Tom Tromey  <tom@tromey.com>
+
+	* configure: Rebuild.
+	* configure.ac: Disallow the combination of -static-libstdc++ and
+	source highlight.
+	* source-cache.c (get_language_name): Handle rust.
+	(source_cache::get_source_lines): Ignore highlighting exceptions.
+
 2019-06-28  Sergio Durigan Junior  <sergiodj@redhat.com>
 
 	PR breakpoints/24541
diff --git a/gdb/configure b/gdb/configure
index 854837c50a..866564fbe6 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -11503,6 +11503,12 @@ $as_echo "no - pkg-config not found" >&6; }
       as_fn_error $? "pkg-config was not found in your system" "$LINENO" 5
     fi
   else
+    case "$LDFLAGS" in
+      *static-libstdc*)
+        as_fn_error $? "source highlight is incompatible with -static-libstdc++; either use --disable-source-highlight or --without-static-standard-libraries" "$LINENO" 5
+        ;;
+    esac
+
     if ${pkg_config_prog_path} --exists source-highlight; then
       SRCHIGH_CFLAGS=`${pkg_config_prog_path} --cflags source-highlight`
       SRCHIGH_LIBS=`${pkg_config_prog_path} --libs source-highlight`
diff --git a/gdb/configure.ac b/gdb/configure.ac
index 1527585839..0805827adf 100644
--- a/gdb/configure.ac
+++ b/gdb/configure.ac
@@ -1251,6 +1251,14 @@ if test "${enable_source_highlight}" != "no"; then
       AC_MSG_ERROR([pkg-config was not found in your system])
     fi
   else
+    case "$LDFLAGS" in
+      *static-libstdc*)
+        AC_MSG_ERROR([source highlight is incompatible with -static-libstdc++; dnl
+either use --disable-source-highlight or dnl
+--without-static-standard-libraries])
+        ;;
+    esac
+
     if ${pkg_config_prog_path} --exists source-highlight; then
       SRCHIGH_CFLAGS=`${pkg_config_prog_path} --cflags source-highlight`
       SRCHIGH_LIBS=`${pkg_config_prog_path} --libs source-highlight`
diff --git a/gdb/source-cache.c b/gdb/source-cache.c
index 5eae02082d..77f92879fd 100644
--- a/gdb/source-cache.c
+++ b/gdb/source-cache.c
@@ -156,8 +156,7 @@ get_language_name (enum language lang)
       break;
 
     case language_rust:
-      /* Not handled by Source Highlight.  */
-      break;
+      return "rust.lang";
 
     case language_ada:
       return "ada.lang";
@@ -216,18 +215,30 @@ source_cache::get_source_lines (struct symtab *s, int first_line,
 	      srchilite::SourceHighlight highlighter ("esc.outlang");
 	      highlighter.setStyleFile("esc.style");
 
-	      std::ostringstream output;
-	      highlighter.highlight (input, output, lang_name, fullname);
+	      try
+		{
+		  std::ostringstream output;
+		  highlighter.highlight (input, output, lang_name, fullname);
 
-	      source_text result = { fullname, output.str () };
-	      m_source_map.push_back (std::move (result));
+		  source_text result = { fullname, output.str () };
+		  m_source_map.push_back (std::move (result));
 
-	      if (m_source_map.size () > MAX_ENTRIES)
-		m_source_map.erase (m_source_map.begin ());
+		  if (m_source_map.size () > MAX_ENTRIES)
+		    m_source_map.erase (m_source_map.begin ());
 
-	      *lines = extract_lines (m_source_map.back (), first_line,
-				      last_line);
-	      return true;
+		  *lines = extract_lines (m_source_map.back (), first_line,
+					  last_line);
+		  return true;
+		}
+	      catch (...)
+		{
+		  /* Source Highlight will throw an exception if
+		     highlighting fails.  One possible reason it can fail
+		     is if the language is unknown -- which matters to gdb
+		     because Rust support wasn't added until after 3.1.8.
+		     Ignore exceptions here and fall back to
+		     un-highlighted text. */
+		}
 	    }
 	}
     }