Warn rather than panic on unknown namespace prefix

When a #defined token was used before a namespace, like so (#1676):

    #define nssv_inline_ns inline
    nssv_inline_ns namespace literals {}

bindgen would crash when encountering the unknown token preceding the
namespace token. This is because we don't get to see "past" the ifdef to
the underlying token. The true fix to this is to find a way to extract
ifdef info through clang, but for the time being we simply change the
panic into a warning when such a token is encountered, and then proceed
as if it were empty.

Fixes #1676.

3 files changed, 30 insertions, 3 deletions

diff --git a/src/ir/context.rs b/src/ir/context.rs
index 127c0a24..384edb95 100644
--- a/src/ir/context.rs
+++ b/src/ir/context.rs
@@ -2166,10 +2166,27 @@ If you encounter an error missing from this list, please file an issue or a PR!"
                     }
                     break;
                 }
-                _ => {
+                spelling if !found_namespace_keyword => {
+                    // This is _likely_, but not certainly, a macro that's been placed just before
+                    // the namespace keyword. Unfortunately, clang tokens don't let us easily see
+                    // through the ifdef tokens, so we don't know what this token should really be.
+                    // Instead of panicking though, we warn the user that we assumed the token was
+                    // blank, and then move on.
+                    //
+                    // See also https://github.com/rust-lang/rust-bindgen/issues/1676.
+                    warn!(
+                        "Ignored unknown namespace prefix '{}' at {:?} in {:?}",
+                        String::from_utf8_lossy(spelling),
+                        token,
+                        cursor
+                    );
+                }
+                spelling => {
                     panic!(
-                        "Unknown token while processing namespace: {:?}",
-                        token
+                        "Unknown token '{}' while processing namespace at {:?} in {:?}",
+                        String::from_utf8_lossy(spelling),
+                        token,
+                        cursor
                     );
                 }
             }
diff --git a/tests/expectations/tests/issue-1676-macro-namespace-prefix.rs b/tests/expectations/tests/issue-1676-macro-namespace-prefix.rs
new file mode 100644
index 00000000..d6776794
--- /dev/null
+++ b/tests/expectations/tests/issue-1676-macro-namespace-prefix.rs
@@ -0,0 +1,8 @@
+/* automatically generated by rust-bindgen */
+
+#![allow(
+    dead_code,
+    non_snake_case,
+    non_camel_case_types,
+    non_upper_case_globals
+)]
diff --git a/tests/headers/issue-1676-macro-namespace-prefix.hpp b/tests/headers/issue-1676-macro-namespace-prefix.hpp
new file mode 100644
index 00000000..297927b6
--- /dev/null
+++ b/tests/headers/issue-1676-macro-namespace-prefix.hpp
@@ -0,0 +1,2 @@
+#define nssv_inline_ns inline
+nssv_inline_ns namespace literals {}