Sema: add default value here note to invalid comptime field store error

src/Module.zig

@@ -2704,6 +2704,18 @@ pub const SrcLoc = struct {
                     else => unreachable,
                 }
             },
+            .node_offset_field_default => |node_off| {
+                const tree = try src_loc.file_scope.getTree(gpa);
+                const node_tags = tree.nodes.items(.tag);
+                const parent_node = src_loc.declRelativeToNodeIndex(node_off);
+
+                const full: Ast.full.ContainerField = switch (node_tags[parent_node]) {
+                    .container_field => tree.containerField(parent_node),
+                    .container_field_init => tree.containerFieldInit(parent_node),
+                    else => unreachable,
+                };
+                return nodeToSpan(tree, full.ast.value_expr);
+            },
         }
     }
 
@@ -3021,6 +3033,9 @@ pub const LazySrcLoc = union(enum) {
     /// The source location points to the tag type of an union or an enum.
     /// The Decl is determined contextually.
     node_offset_container_tag: i32,
+    /// The source location points to the default value of a field.
+    /// The Decl is determined contextually.
+    node_offset_field_default: i32,
 
     pub const nodeOffset = if (TracedOffset.want_tracing) nodeOffsetDebug else nodeOffsetRelease;
 
@@ -3098,6 +3113,7 @@ pub const LazySrcLoc = union(enum) {
             .node_offset_ptr_bitoffset,
             .node_offset_ptr_hostsize,
             .node_offset_container_tag,
+            .node_offset_field_default,
             => .{
                 .file_scope = decl.getFileScope(),
                 .parent_decl_node = decl.src_node,

src/Sema.zig

@@ -1789,6 +1789,24 @@ fn failWithIntegerOverflow(sema: *Sema, block: *Block, src: LazySrcLoc, int_ty:
     });
 }
 
+fn failWithInvalidComptimeFieldStore(sema: *Sema, block: *Block, init_src: LazySrcLoc, container_ty: Type, field_index: usize) CompileError {
+    const msg = msg: {
+        const msg = try sema.errMsg(block, init_src, "value stored in comptime field does not match the default value of the field", .{});
+        errdefer msg.destroy(sema.gpa);
+
+        const decl_index = container_ty.getOwnerDeclOrNull() orelse break :msg msg;
+
+        const tree = try sema.getAstTree(block);
+        const decl = sema.mod.declPtr(decl_index);
+        const field_src = enumFieldSrcLoc(decl, tree.*, container_ty.getNodeOffset(), field_index);
+        const default_value_src: LazySrcLoc = .{ .node_offset_field_default = field_src.node_offset.x };
+
+        try sema.errNote(block, default_value_src, msg, "default value set here", .{});
+        break :msg msg;
+    };
+    return sema.failWithOwnedErrorMsg(block, msg);
+}
+
 /// We don't return a pointer to the new error note because the pointer
 /// becomes invalid when you add another one.
 fn errNote(
@@ -14542,8 +14560,7 @@ fn zirStructInit(
                 };
 
                 if (!init_val.eql(default_value, resolved_ty.structFieldType(field_index), sema.mod)) {
-                    // TODO add note showing where default value is provided
-                    return sema.fail(block, field_src, "value stored in comptime field does not match the default value of the field", .{});
+                    return sema.failWithInvalidComptimeFieldStore(block, field_src, resolved_ty, field_index);
                 }
             };
         }
@@ -22379,7 +22396,7 @@ fn storePtrVal(
         .direct => |val_ptr| {
             if (mut_kit.decl_ref_mut.runtime_index == .comptime_field_ptr) {
                 if (!operand_val.eql(val_ptr.*, operand_ty, sema.mod)) {
-                    // TODO add note showing where default value is provided
+                    // TODO use failWithInvalidComptimeFieldStore
                     return sema.fail(block, src, "value stored in comptime field does not match the default value of the field", .{});
                 }
                 return;
@@ -23754,8 +23771,7 @@ fn coerceTupleToStruct(
             };
 
             if (!init_val.eql(field.default_val, field.ty, sema.mod)) {
-                // TODO add note showing where default value is provided
-                return sema.fail(block, field_src, "value stored in comptime field does not match the default value of the field", .{});
+                return sema.failWithInvalidComptimeFieldStore(block, field_src, inst_ty, i);
             }
         }
         if (runtime_src == null) {

src/type.zig

@@ -5714,6 +5714,10 @@ pub const Type = extern union {
     }
 
     pub fn getOwnerDecl(ty: Type) Module.Decl.Index {
+        return ty.getOwnerDeclOrNull() orelse unreachable;
+    }
+
+    pub fn getOwnerDeclOrNull(ty: Type) ?Module.Decl.Index {
         switch (ty.tag()) {
             .enum_full, .enum_nonexhaustive => {
                 const enum_full = ty.cast(Payload.EnumFull).?.data;
@@ -5753,7 +5757,7 @@ pub const Type = extern union {
             .type_info,
             => unreachable, // These need to be resolved earlier.
 
-            else => unreachable,
+            else => return null,
         }
     }