Improve debug symbol names to avoid ambiguity and work better with MSVC's debugger

There are several cases where names of types and functions in the debug info are either ambiguous, or not helpful, such as including ambiguous placeholders (e.g., `{{impl}}`, `{{closure}}` or `dyn _'`) or dropping qualifications (e.g., for dynamic types).

Instead, each debug symbol name should be unique and useful:
* Include disambiguators for anonymous `DefPathDataName` (closures and generators), and unify their formatting when used as a path-qualifier vs item being qualified.
* Qualify the principal trait for dynamic types.
* If there is no principal trait for a dynamic type, emit all other traits instead.
* Respect the `qualified` argument when emitting ref and pointer types.
* For implementations, emit the disambiguator.
* Print const generics when emitting generic parameters or arguments.

Additionally, when targeting MSVC, its debugger treats many command arguments as C++ expressions, even when the argument is defined to be a symbol name. As such names in the debug info need to be more C++-like to be parsed correctly:
* Avoid characters with special meaning (`#`, `[`, `"`, `+`).
* Never start a name with `<` or `{` as this is treated as an operator.
* `>>` is always treated as a right-shift, even when parsing generic arguments (so add a space to avoid this).
* Emit function declarations using C/C++ style syntax (e.g., leading return type).
* Emit arrays as a synthetic `array$<type, size>` type.
* Include a `$` in all synthetic types as this is a legal character for C++, but not Rust (thus we avoid collisions with user types).

1 files changed, 19 insertions, 7 deletions

diff --git a/src/tools/compiletest/src/runtest.rs b/src/tools/compiletest/src/runtest.rs
index 6a1faee1d8e..49731b2d7dc 100644
--- a/src/tools/compiletest/src/runtest.rs
+++ b/src/tools/compiletest/src/runtest.rs
@@ -778,6 +778,14 @@ impl<'test> TestCx<'test> {
         script_str.push_str("version\n"); // List CDB (and more) version info in test output
         script_str.push_str(".nvlist\n"); // List loaded `*.natvis` files, bulk of custom MSVC debug
 
+        // If a .js file exists next to the source file being tested, then this is a JavaScript
+        // debugging extension that needs to be loaded.
+        let mut js_extension = self.testpaths.file.clone();
+        js_extension.set_extension("cdb.js");
+        if js_extension.exists() {
+            script_str.push_str(&format!(".scriptload \"{}\"\n", js_extension.to_string_lossy()));
+        }
+
         // Set breakpoints on every line that contains the string "#break"
         let source_file_name = self.testpaths.file.file_name().unwrap().to_string_lossy();
         for line in &breakpoint_lines {
@@ -2329,13 +2337,17 @@ impl<'test> TestCx<'test> {
         // useful flag.
         //
         // For now, though…
-        if let Some(rev) = self.revision {
-            let prefixes = format!("CHECK,{}", rev);
-            if self.config.llvm_version.unwrap_or(0) >= 130000 {
-                filecheck.args(&["--allow-unused-prefixes", "--check-prefixes", &prefixes]);
-            } else {
-                filecheck.args(&["--check-prefixes", &prefixes]);
-            }
+        let prefix_for_target =
+            if self.config.target.contains("msvc") { "MSVC" } else { "NONMSVC" };
+        let prefixes = if let Some(rev) = self.revision {
+            format!("CHECK,{},{}", prefix_for_target, rev)
+        } else {
+            format!("CHECK,{}", prefix_for_target)
+        };
+        if self.config.llvm_version.unwrap_or(0) >= 130000 {
+            filecheck.args(&["--allow-unused-prefixes", "--check-prefixes", &prefixes]);
+        } else {
+            filecheck.args(&["--check-prefixes", &prefixes]);
         }
         self.compose_and_run(filecheck, "", None, None)
     }