Sema: cap depth of value printing in type names

Certain types (notably, `std.ComptimeStringMap`) were resulting in excessively
long type names when instantiated, which in turn resulted in excessively long
symbol names. These are problematic for two reasons:

* Symbol names are sometimes read by humans -- they ought to be readable.
* Some other applications (looking at you, xcode) trip on very long symbol names.

To work around this for now, we cap the depth of value printing at 1, as opposed
to the normal 3. This doesn't guarantee anything -- there could still be, for
instance, an incredibly long aggregate -- but it works around the issue in
practice for the time being.

Author: mlugg

src/Sema.zig

@@ -2869,14 +2869,14 @@ fn createAnonymousDeclTypeNamed(
     anon_prefix: []const u8,
     inst: ?Zir.Inst.Index,
 ) !InternPool.DeclIndex {
-    const mod = sema.mod;
-    const ip = &mod.intern_pool;
+    const zcu = sema.mod;
+    const ip = &zcu.intern_pool;
     const gpa = sema.gpa;
     const namespace = block.namespace;
-    const src_decl = mod.declPtr(block.src_decl);
+    const src_decl = zcu.declPtr(block.src_decl);
     const src_node = src_decl.relativeToNodeIndex(src.node_offset.x);
-    const new_decl_index = try mod.allocateNewDecl(namespace, src_node);
-    errdefer mod.destroyDecl(new_decl_index);
+    const new_decl_index = try zcu.allocateNewDecl(namespace, src_node);
+    errdefer zcu.destroyDecl(new_decl_index);
 
     switch (name_strategy) {
         .anon => {
@@ -2887,15 +2887,15 @@ fn createAnonymousDeclTypeNamed(
             // This name is also used as the key in the parent namespace so it cannot be
             // renamed.
 
-            const name = mod.intern_pool.getOrPutStringFmt(gpa, "{}__{s}_{d}", .{
-                src_decl.name.fmt(&mod.intern_pool), anon_prefix, @intFromEnum(new_decl_index),
+            const name = ip.getOrPutStringFmt(gpa, "{}__{s}_{d}", .{
+                src_decl.name.fmt(ip), anon_prefix, @intFromEnum(new_decl_index),
             }, .no_embedded_nulls) catch unreachable;
-            try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, val, name);
+            try zcu.initNewAnonDecl(new_decl_index, src_decl.src_line, val, name);
             return new_decl_index;
         },
         .parent => {
-            const name = mod.declPtr(block.src_decl).name;
-            try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, val, name);
+            const name = zcu.declPtr(block.src_decl).name;
+            try zcu.initNewAnonDecl(new_decl_index, src_decl.src_line, val, name);
             return new_decl_index;
         },
         .func => {
@@ -2906,7 +2906,7 @@ fn createAnonymousDeclTypeNamed(
             defer buf.deinit();
 
             const writer = buf.writer();
-            try writer.print("{}(", .{mod.declPtr(block.src_decl).name.fmt(&mod.intern_pool)});
+            try writer.print("{}(", .{zcu.declPtr(block.src_decl).name.fmt(ip)});
 
             var arg_i: usize = 0;
             for (fn_info.param_body) |zir_inst| switch (zir_tags[@intFromEnum(zir_inst)]) {
@@ -2921,7 +2921,17 @@ fn createAnonymousDeclTypeNamed(
                         return sema.createAnonymousDeclTypeNamed(block, src, val, .anon, anon_prefix, null);
 
                     if (arg_i != 0) try writer.writeByte(',');
-                    try writer.print("{}", .{arg_val.fmtValue(sema.mod, sema)});
+
+                    // Limiting the depth here helps avoid type names getting too long, which
+                    // in turn helps to avoid unreasonably long symbol names for namespaced
+                    // symbols. Such names should ideally be human-readable, and additionally,
+                    // some tooling may not support very long symbol names.
+                    try writer.print("{}", .{Value.fmtValueFull(.{
+                        .val = arg_val,
+                        .mod = zcu,
+                        .opt_sema = sema,
+                        .depth = 1,
+                    })});
 
                     arg_i += 1;
                     continue;
@@ -2930,8 +2940,8 @@ fn createAnonymousDeclTypeNamed(
             };
 
             try writer.writeByte(')');
-            const name = try mod.intern_pool.getOrPutString(gpa, buf.items, .no_embedded_nulls);
-            try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, val, name);
+            const name = try ip.getOrPutString(gpa, buf.items, .no_embedded_nulls);
+            try zcu.initNewAnonDecl(new_decl_index, src_decl.src_line, val, name);
             return new_decl_index;
         },
         .dbg_var => {
@@ -2942,10 +2952,10 @@ fn createAnonymousDeclTypeNamed(
                 .dbg_var_ptr, .dbg_var_val => {
                     if (zir_data[i].str_op.operand != ref) continue;
 
-                    const name = try mod.intern_pool.getOrPutStringFmt(gpa, "{}.{s}", .{
-                        src_decl.name.fmt(&mod.intern_pool), zir_data[i].str_op.getStr(sema.code),
+                    const name = try ip.getOrPutStringFmt(gpa, "{}.{s}", .{
+                        src_decl.name.fmt(ip), zir_data[i].str_op.getStr(sema.code),
                     }, .no_embedded_nulls);
-                    try mod.initNewAnonDecl(new_decl_index, src_decl.src_line, val, name);
+                    try zcu.initNewAnonDecl(new_decl_index, src_decl.src_line, val, name);
                     return new_decl_index;
                 },
                 else => {},

src/Value.zig

@@ -44,9 +44,14 @@ pub fn fmtValue(val: Value, mod: *Module, opt_sema: ?*Sema) std.fmt.Formatter(pr
         .val = val,
         .mod = mod,
         .opt_sema = opt_sema,
+        .depth = 3,
     } };
 }
 
+pub fn fmtValueFull(ctx: print_value.FormatContext) std.fmt.Formatter(print_value.format) {
+    return .{ .data = ctx };
+}
+
 /// Converts `val` to a null-terminated string stored in the InternPool.
 /// Asserts `val` is an array of `u8`
 pub fn toIpString(val: Value, ty: Type, mod: *Module) !InternPool.NullTerminatedString {

src/print_value.zig

@@ -14,10 +14,11 @@ const Target = std.Target;
 const max_aggregate_items = 100;
 const max_string_len = 256;
 
-const FormatContext = struct {
+pub const FormatContext = struct {
     val: Value,
     mod: *Module,
     opt_sema: ?*Sema,
+    depth: u8,
 };
 
 pub fn format(
@@ -28,7 +29,7 @@ pub fn format(
 ) !void {
     _ = options;
     comptime std.debug.assert(fmt.len == 0);
-    return print(ctx.val, writer, 3, ctx.mod, ctx.opt_sema) catch |err| switch (err) {
+    return print(ctx.val, writer, ctx.depth, ctx.mod, ctx.opt_sema) catch |err| switch (err) {
         error.OutOfMemory => @panic("OOM"), // We're not allowed to return this from a format function
         error.ComptimeBreak, error.ComptimeReturn => unreachable,
         error.AnalysisFail, error.NeededSourceLocation => unreachable, // TODO: re-evaluate when we use `opt_sema` more fully