From d717c96877355090ea3a8e3662a2584eea02445c Mon Sep 17 00:00:00 2001
From: mlugg <mlugg@mlugg.co.uk>
Date: Thu, 15 May 2025 13:18:08 +0100
Subject: compiler: include inline calls in the reference trace

Inline calls which happened in the erroring `AnalUnit` still show as
error notes, because they tend to make very important context (e.g. to
see how comptime values propagate through them). However, "earlier"
inline calls are still useful to see to understand how something is
being referenced, so we should include them in the reference trace.
---
 src/Compilation.zig | 66 ++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 45 insertions(+), 21 deletions(-)

(limited to 'src/Compilation.zig')

diff --git a/src/Compilation.zig b/src/Compilation.zig
index 57e36bfbf7..d3cf9e8f38 100644
--- a/src/Compilation.zig
+++ b/src/Compilation.zig
@@ -3681,32 +3681,27 @@ pub fn addModuleErrorMsg(
             const ref = maybe_ref orelse break;
             const gop = try seen.getOrPut(gpa, ref.referencer);
             if (gop.found_existing) break;
-            if (ref_traces.items.len < max_references) skip: {
-                const src = ref.src.upgrade(zcu);
-                const source = try src.file_scope.getSource(gpa);
-                const span = try src.span(gpa);
-                const loc = std.zig.findLineColumn(source.bytes, span.main);
-                const rt_file_path = try src.file_scope.fullPath(gpa);
-                defer gpa.free(rt_file_path);
-                const name = switch (ref.referencer.unwrap()) {
+            if (ref_traces.items.len < max_references) {
+                var last_call_src = ref.src;
+                var opt_inline_frame = ref.inline_frame;
+                while (opt_inline_frame.unwrap()) |inline_frame| {
+                    const f = inline_frame.ptr(zcu).*;
+                    const func_nav = ip.indexToKey(f.callee).func.owner_nav;
+                    const func_name = ip.getNav(func_nav).name.toSlice(ip);
+                    try addReferenceTraceFrame(zcu, eb, &ref_traces, func_name, last_call_src, true);
+                    last_call_src = f.call_src;
+                    opt_inline_frame = f.parent;
+                }
+                const root_name: ?[]const u8 = switch (ref.referencer.unwrap()) {
                     .@"comptime" => "comptime",
                     .nav_val, .nav_ty => |nav| ip.getNav(nav).name.toSlice(ip),
                     .type => |ty| Type.fromInterned(ty).containerTypeName(ip).toSlice(ip),
                     .func => |f| ip.getNav(zcu.funcInfo(f).owner_nav).name.toSlice(ip),
-                    .memoized_state => break :skip,
+                    .memoized_state => null,
                 };
-                try ref_traces.append(gpa, .{
-                    .decl_name = try eb.addString(name),
-                    .src_loc = try eb.addSourceLocation(.{
-                        .src_path = try eb.addString(rt_file_path),
-                        .span_start = span.start,
-                        .span_main = span.main,
-                        .span_end = span.end,
-                        .line = @intCast(loc.line),
-                        .column = @intCast(loc.column),
-                        .source_line = 0,
-                    }),
-                });
+                if (root_name) |n| {
+                    try addReferenceTraceFrame(zcu, eb, &ref_traces, n, last_call_src, false);
+                }
             }
             referenced_by = ref.referencer;
         }
@@ -3786,6 +3781,35 @@ pub fn addModuleErrorMsg(
     }
 }
 
+fn addReferenceTraceFrame(
+    zcu: *Zcu,
+    eb: *ErrorBundle.Wip,
+    ref_traces: *std.ArrayListUnmanaged(ErrorBundle.ReferenceTrace),
+    name: []const u8,
+    lazy_src: Zcu.LazySrcLoc,
+    inlined: bool,
+) !void {
+    const gpa = zcu.gpa;
+    const src = lazy_src.upgrade(zcu);
+    const source = try src.file_scope.getSource(gpa);
+    const span = try src.span(gpa);
+    const loc = std.zig.findLineColumn(source.bytes, span.main);
+    const rt_file_path = try src.file_scope.fullPath(gpa);
+    defer gpa.free(rt_file_path);
+    try ref_traces.append(gpa, .{
+        .decl_name = try eb.printString("{s}{s}", .{ name, if (inlined) " [inlined]" else "" }),
+        .src_loc = try eb.addSourceLocation(.{
+            .src_path = try eb.addString(rt_file_path),
+            .span_start = span.start,
+            .span_main = span.main,
+            .span_end = span.end,
+            .line = @intCast(loc.line),
+            .column = @intCast(loc.column),
+            .source_line = 0,
+        }),
+    });
+}
+
 pub fn addZirErrorMessages(eb: *ErrorBundle.Wip, file: *Zcu.File) !void {
     const gpa = eb.gpa;
     const src_path = try file.fullPath(gpa);
-- 
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