progress towards semantic error serialization

Introduces std.zig.ErrorBundle which is a trivially serializeable set
of compilation errors. This is in the standard library so that both
the compiler and the build runner can use it. The idea is they will
use it to communicate compilation errors over a binary protocol.

The binary encoding of ErrorBundle is a bit problematic - I got a little
too aggressive with compaction. I need to change it in a follow-up
commit to use some indirection in the error message list, otherwise
iteration is too unergonomic. In fact it's so problematic right now that
the logic getAllErrorsAlloc() actually fails to produce a viable
ErrorBundle because it puts SourceLocation data in between the root
level ErrorMessage data.

This commit has a simplification - redundant logic for rendering AST
errors to stderr has been removed in favor of moving the logic for
lowering AST errors into AstGen. So even if we get parse errors, the
errors will get lowered into ZIR before being reported. I believe this
will be useful when working on --autofix. Either way, some redundant
brittle logic was happily deleted.

In Compilation, updateSubCompilation() is improved to properly perform
error reporting when a sub-compilation object fails. It no longer dumps
directly to stderr; instead it populates an ErrorBundle object, which
gets added to the parent one during getAllErrorsAlloc().

In package fetching code, instead of dumping directly to stderr, it now
populates an ErrorBundle object, and gets properly reported at the CLI
layer of abstraction.

1 files changed, 11 insertions, 14 deletions

diff --git a/src/Sema.zig b/src/Sema.zig
index 8b6c269246..237936547e 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -2211,29 +2211,26 @@ pub fn fail(
 
 fn failWithOwnedErrorMsg(sema: *Sema, err_msg: *Module.ErrorMsg) CompileError {
     @setCold(true);
+    const gpa = sema.gpa;
 
     if (crash_report.is_enabled and sema.mod.comp.debug_compile_errors) {
         if (err_msg.src_loc.lazy == .unneeded) return error.NeededSourceLocation;
-        var arena = std.heap.ArenaAllocator.init(sema.gpa);
-        errdefer arena.deinit();
-        var errors = std.ArrayList(Compilation.AllErrors.Message).init(sema.gpa);
-        defer errors.deinit();
-
-        Compilation.AllErrors.add(sema.mod, &arena, &errors, err_msg.*) catch unreachable;
-
+        var errors: std.zig.ErrorBundle = undefined;
+        errors.init(gpa) catch unreachable;
+        Compilation.addModuleErrorMsg(gpa, &errors, err_msg.*) catch unreachable;
         std.debug.print("compile error during Sema:\n", .{});
-        Compilation.AllErrors.Message.renderToStdErr(errors.items[0], .no_color);
+        errors.renderToStdErr(.no_color);
         crash_report.compilerPanic("unexpected compile error occurred", null, null);
     }
 
     const mod = sema.mod;
     ref: {
-        errdefer err_msg.destroy(mod.gpa);
+        errdefer err_msg.destroy(gpa);
         if (err_msg.src_loc.lazy == .unneeded) {
             return error.NeededSourceLocation;
         }
-        try mod.failed_decls.ensureUnusedCapacity(mod.gpa, 1);
-        try mod.failed_files.ensureUnusedCapacity(mod.gpa, 1);
+        try mod.failed_decls.ensureUnusedCapacity(gpa, 1);
+        try mod.failed_files.ensureUnusedCapacity(gpa, 1);
 
         const max_references = blk: {
             if (sema.mod.comp.reference_trace) |num| break :blk num;
@@ -2243,11 +2240,11 @@ fn failWithOwnedErrorMsg(sema: *Sema, err_msg: *Module.ErrorMsg) CompileError {
         };
 
         var referenced_by = if (sema.func) |some| some.owner_decl else sema.owner_decl_index;
-        var reference_stack = std.ArrayList(Module.ErrorMsg.Trace).init(sema.gpa);
+        var reference_stack = std.ArrayList(Module.ErrorMsg.Trace).init(gpa);
         defer reference_stack.deinit();
 
         // Avoid infinite loops.
-        var seen = std.AutoHashMap(Module.Decl.Index, void).init(sema.gpa);
+        var seen = std.AutoHashMap(Module.Decl.Index, void).init(gpa);
         defer seen.deinit();
 
         var cur_reference_trace: u32 = 0;
@@ -2288,7 +2285,7 @@ fn failWithOwnedErrorMsg(sema: *Sema, err_msg: *Module.ErrorMsg) CompileError {
     if (gop.found_existing) {
         // If there are multiple errors for the same Decl, prefer the first one added.
         sema.err = null;
-        err_msg.destroy(mod.gpa);
+        err_msg.destroy(gpa);
     } else {
         sema.err = err_msg;
         gop.value_ptr.* = err_msg;