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, 53 insertions, 55 deletions

diff --git a/src/Package.zig b/src/Package.zig
index 87d52197bd..febcc51788 100644
--- a/src/Package.zig
+++ b/src/Package.zig
@@ -225,7 +225,7 @@ pub fn fetchAndAddDependencies(
     dependencies_source: *std.ArrayList(u8),
     build_roots_source: *std.ArrayList(u8),
     name_prefix: []const u8,
-    color: main.Color,
+    error_bundle: *std.zig.ErrorBundle,
     all_modules: *AllModules,
 ) !void {
     const max_bytes = 10 * 1024 * 1024;
@@ -250,7 +250,7 @@ pub fn fetchAndAddDependencies(
 
     if (ast.errors.len > 0) {
         const file_path = try directory.join(arena, &.{Manifest.basename});
-        try main.printErrsMsgToStdErr(gpa, arena, ast, file_path, color);
+        try main.putAstErrorsIntoBundle(gpa, ast, file_path, error_bundle);
         return error.PackageFetchFailed;
     }
 
@@ -258,23 +258,18 @@ pub fn fetchAndAddDependencies(
     defer manifest.deinit(gpa);
 
     if (manifest.errors.len > 0) {
-        const ttyconf: std.debug.TTY.Config = switch (color) {
-            .auto => std.debug.detectTTYConfig(std.io.getStdErr()),
-            .on => .escape_codes,
-            .off => .no_color,
-        };
         const file_path = try directory.join(arena, &.{Manifest.basename});
         for (manifest.errors) |msg| {
-            Report.renderErrorMessage(ast, file_path, ttyconf, msg, &.{});
+            try Report.addErrorMessage(gpa, ast, file_path, error_bundle, 0, msg);
         }
         return error.PackageFetchFailed;
     }
 
     const report: Report = .{
+        .gpa = gpa,
         .ast = &ast,
         .directory = directory,
-        .color = color,
-        .arena = arena,
+        .error_bundle = error_bundle,
     };
 
     var any_error = false;
@@ -307,7 +302,7 @@ pub fn fetchAndAddDependencies(
             dependencies_source,
             build_roots_source,
             sub_prefix,
-            color,
+            error_bundle,
             all_modules,
         );
 
@@ -348,10 +343,10 @@ pub fn createFilePkg(
 }
 
 const Report = struct {
+    gpa: Allocator,
     ast: *const std.zig.Ast,
     directory: Compilation.Directory,
-    color: main.Color,
-    arena: Allocator,
+    error_bundle: *std.zig.ErrorBundle,
 
     fn fail(
         report: Report,
@@ -359,52 +354,48 @@ const Report = struct {
         comptime fmt_string: []const u8,
         fmt_args: anytype,
     ) error{ PackageFetchFailed, OutOfMemory } {
-        return failWithNotes(report, &.{}, tok, fmt_string, fmt_args);
-    }
+        const gpa = report.gpa;
 
-    fn failWithNotes(
-        report: Report,
-        notes: []const Compilation.AllErrors.Message,
-        tok: std.zig.Ast.TokenIndex,
-        comptime fmt_string: []const u8,
-        fmt_args: anytype,
-    ) error{ PackageFetchFailed, OutOfMemory } {
-        const ttyconf: std.debug.TTY.Config = switch (report.color) {
-            .auto => std.debug.detectTTYConfig(std.io.getStdErr()),
-            .on => .escape_codes,
-            .off => .no_color,
-        };
-        const file_path = try report.directory.join(report.arena, &.{Manifest.basename});
-        renderErrorMessage(report.ast.*, file_path, ttyconf, .{
+        const file_path = try report.directory.join(gpa, &.{Manifest.basename});
+        defer gpa.free(file_path);
+
+        const msg = try std.fmt.allocPrint(gpa, fmt_string, fmt_args);
+        defer gpa.free(msg);
+
+        try addErrorMessage(report.gpa, report.ast.*, file_path, report.error_bundle, 0, .{
             .tok = tok,
             .off = 0,
-            .msg = try std.fmt.allocPrint(report.arena, fmt_string, fmt_args),
-        }, notes);
+            .msg = msg,
+        });
+
         return error.PackageFetchFailed;
     }
 
-    fn renderErrorMessage(
+    fn addErrorMessage(
+        gpa: Allocator,
         ast: std.zig.Ast,
         file_path: []const u8,
-        ttyconf: std.debug.TTY.Config,
+        eb: *std.zig.ErrorBundle,
+        notes_len: u32,
         msg: Manifest.ErrorMessage,
-        notes: []const Compilation.AllErrors.Message,
-    ) void {
+    ) error{OutOfMemory}!void {
         const token_starts = ast.tokens.items(.start);
         const start_loc = ast.tokenLocation(0, msg.tok);
-        Compilation.AllErrors.Message.renderToStdErr(.{ .src = .{
-            .msg = msg.msg,
-            .src_path = file_path,
-            .line = @intCast(u32, start_loc.line),
-            .column = @intCast(u32, start_loc.column),
-            .span = .{
-                .start = token_starts[msg.tok],
-                .end = @intCast(u32, token_starts[msg.tok] + ast.tokenSlice(msg.tok).len),
-                .main = token_starts[msg.tok] + msg.off,
-            },
-            .source_line = ast.source[start_loc.line_start..start_loc.line_end],
-            .notes = notes,
-        } }, ttyconf);
+
+        try eb.addErrorMessage(gpa, .{
+            .msg = try eb.addString(gpa, msg.msg),
+            .src_loc = try eb.addSourceLocation(gpa, .{
+                .src_path = try eb.addString(gpa, file_path),
+                .span_start = token_starts[msg.tok],
+                .span_end = @intCast(u32, token_starts[msg.tok] + ast.tokenSlice(msg.tok).len),
+                .span_main = token_starts[msg.tok] + msg.off,
+                .line = @intCast(u32, start_loc.line),
+                .column = @intCast(u32, start_loc.column),
+                .source_line = try eb.addString(gpa, ast.source[start_loc.line_start..start_loc.line_end]),
+            }),
+            .notes_len = notes_len,
+        });
+        eb.incrementCount(1);
     }
 };
 
@@ -504,9 +495,7 @@ fn fetchAndUnpack(
             // by default, so the same logic applies for buffering the reader as for gzip.
             try unpackTarball(gpa, &req, tmp_directory.handle, std.compress.xz);
         } else {
-            return report.fail(dep.url_tok, "unknown file extension for path '{s}'", .{
-                uri.path,
-            });
+            return report.fail(dep.url_tok, "unknown file extension for path '{s}'", .{uri.path});
         }
 
         // TODO: delete files not included in the package prior to computing the package hash.
@@ -533,10 +522,19 @@ fn fetchAndUnpack(
             });
         }
     } else {
-        const notes: [1]Compilation.AllErrors.Message = .{.{ .plain = .{
-            .msg = try std.fmt.allocPrint(report.arena, "expected .hash = \"{s}\",", .{&actual_hex}),
-        } }};
-        return report.failWithNotes(&notes, dep.url_tok, "url field is missing corresponding hash field", .{});
+        const file_path = try report.directory.join(gpa, &.{Manifest.basename});
+        defer gpa.free(file_path);
+
+        const eb = report.error_bundle;
+        try Report.addErrorMessage(gpa, report.ast.*, file_path, eb, 1, .{
+            .tok = dep.url_tok,
+            .off = 0,
+            .msg = "url field is missing corresponding hash field",
+        });
+        try eb.addErrorMessage(gpa, .{
+            .msg = try eb.printString(gpa, "expected .hash = \"{s}\",", .{&actual_hex}),
+        });
+        return error.PackageFetchFailed;
     }
 
     const build_root = try global_cache_directory.join(gpa, &.{pkg_dir_sub_path});