fix(rust): map a Zig standard-library map to std::collections::HashMap (+5)

.trinity/seals/TriGraph.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:e211780c0b7bbd8a861e059d0708e5bea52674ead30efcaa1eebcfdd16cf51dc",
-  "gen_hash_rust": "sha256:97397057eab14046c0a4327554771e1b2096e05c6ec590d54fef76268cf9f0b3",
+  "gen_hash_rust": "sha256:a21c1de6323c0a5301195c9b479469b20273ec5e8ffe093ea8863676aacbce1f",
   "gen_hash_verilog": "sha256:c0bd9cddefce72cfb629855f772f6a0d31cf7b538c6132d8a16859dc17becdf7",
   "gen_hash_zig": "sha256:444d15ecc025e0b172fc8594054a13177a0e5496a32390d4261857b5ef804f90",
   "module": "TriGraph",

.trinity/seals/TriHtml.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:1f8b30b7f71c2bcdcdf216fe8dacbf6f68f3e22f9d8f075c289f3c3beb856c45",
-  "gen_hash_rust": "sha256:223e31bf32dcb00bfec3685414e5859a63256c1903d2abf8c47d79c3855d6d59",
+  "gen_hash_rust": "sha256:5120100890657113985b5476a8fc395a72b81a1277b7a1ae9b0ff6bf0f68adb1",
   "gen_hash_verilog": "sha256:1fa7df852949de5a53c7814c90ff93ae0c4849656379383f877f562d98f06fc2",
   "gen_hash_zig": "sha256:c7ed13bb6e091bcedf263a647fa5a434899da8246b96e6427fa04d4797268e7f",
   "module": "TriHtml",

.trinity/seals/TriLru.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:947ed3a8df75a4a9ee4c54311c70b9edda1739216d72be28f3cfdaf80958303d",
-  "gen_hash_rust": "sha256:c07ab86a7de321ce47095f951e5bc07bc5d3b3f22fa03822694a65c47a08fc0d",
+  "gen_hash_rust": "sha256:9102ac246ade61f92cd79840980dab11b75512a086a587d32d2fb2081204f174",
   "gen_hash_verilog": "sha256:ebf3050832135b9ec9b6e2480889eabd422468317d7d06e3efa054d06df833cc",
   "gen_hash_zig": "sha256:db41d91af86d45b14de051a11a9259b1534b93caa7e01d2c3c4ca2abe0607f5d",
   "module": "TriLru",

.trinity/seals/TriMsgpack.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:2069e8885ebe9049617e38a4e2d0f2a50f59570bb50cd29ee0981e3b17a96027",
-  "gen_hash_rust": "sha256:300a3d600a5b55835279ca4a4d58056198e8df63d5556596d64d6dad6dd7b235",
+  "gen_hash_rust": "sha256:2fc88453916cd34b97a77f7d030cb60286932edd3ee44893dd3ef29e8a482200",
   "gen_hash_verilog": "sha256:f70c08c4cd1f900cc223d58ee2e550d3b02ad321144a659f3dcc4cb1452be32b",
   "gen_hash_zig": "sha256:04a9c694d50297efa8ed0f1d74eaa7f47b8fe92557e52454ed75a7c885c896c1",
   "module": "TriMsgpack",

.trinity/seals/TriSet.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:9613b7c8f320bac36af110397bf7b0d1e290b0c2f86783209c1b4f40962784c4",
-  "gen_hash_rust": "sha256:ab38e31fb8d7d8ec8b37ded2cd1ce6718a64f1efa7b51a709ebfe3be9b6a22da",
+  "gen_hash_rust": "sha256:48a66ec67d9eae55810826dd2a5fb14c48a0bb091cd0164d293a7aa8d8da470f",
   "gen_hash_verilog": "sha256:a3f2edcb48986f07d75d8b5ec7e39b7308b6823f508a8bbcf4d84f1cb9d7e6a5",
   "gen_hash_zig": "sha256:3c40e78d01506a92d08946933a7d75abb7a8aabc3bec4df03d9389c19f5a974d",
   "module": "TriSet",

.trinity/seals/TriTrie.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:dbaea551a83dbeb3302415612fe55402f9f9c24bad77a0abc7903fa5149669ec",
-  "gen_hash_rust": "sha256:57c99ffb2c2dae8b836b14976be847691c2bdc36a4317c045a5e7e0c69e83878",
+  "gen_hash_rust": "sha256:7ce3d8fbeab2e3ebd0653ef061b0444712702bb96063dcad96a8f15d1cc94e26",
   "gen_hash_verilog": "sha256:92be6269928168a86cd2289199bb784ce3383d193966de87fce0e460437de5e9",
   "gen_hash_zig": "sha256:e87caaa2882c44de5510f6e1cbe09afd29ba4443ddc9a7b57a3a6645b3372c43",
   "module": "TriTrie",

.trinity/seals/TriXml.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:c13021e282c10254a2f161577c55e506fb096dff8740997d2ff8dbb6a2bf7683",
-  "gen_hash_rust": "sha256:8472efbec7b2f13cd2c5733556cd19a5e5c717a28d81a094cc754bda1341a291",
+  "gen_hash_rust": "sha256:45236f8613780705b2580a7223c49fee5b621b40ac51d878b60ec3dcd6074547",
   "gen_hash_verilog": "sha256:ef20a47e3fc1296bda60734bbe0b8255375a7c35752327385c1b586c354f863b",
   "gen_hash_zig": "sha256:d82f497edfa15ea7da4c2c48aa7abab230377ead54e73c6145ca40a660290c76",
   "module": "TriXml",

.trinity/seals/api_sdk_contract.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:2a18047c89fb2af3255fe5066f1c35cbba5410cca19598a0fc6c1b0e35ef13a0",
-  "gen_hash_rust": "sha256:28b5de014c24859a2f74e0893707a535295ec8719815f4968bb49098376943e9",
+  "gen_hash_rust": "sha256:8980aeccf629d1dd914cbbd02c717ff0ab08e53b7a72d4c88623c92c04f7c0a9",
   "gen_hash_verilog": "sha256:9bc46f2772e60e074704356e9bb38868a7f263f3cfe251e30a106b82ed41edc3",
   "gen_hash_zig": "sha256:e05074e18d030ac66115f4bd3d65efa2e6a2f76bcd7b27499577d8d47934eb69",
   "module": "sdk_contract",
   "ring": 12,
-  "sealed_at": "2026-09-06T04:36:42Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:67b126ee510d34e78677d12e64b2b2aacf9951410adc6f3338018101e0e112c0",
   "spec_path": "specs/api/sdk_contract.t27"

.trinity/seals/ast.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:fbc813ecf388fc2f9e49d10409608df2cc50cf36339be1b0caf580759b70bc54",
-  "gen_hash_rust": "sha256:cf796b2c39fc159ff964232c2feb3e679f46d71c67f88e4085a41496e131d824",
+  "gen_hash_rust": "sha256:e1895409c636130f9fec6a7b48f812cf1cd8c29bfc99c454f8b7085d53c9058a",
   "gen_hash_verilog": "sha256:13ea818e724f76ac3ef3b457c21d71c31b7b264c3d6c2eee30dc61229eb1eb41",
   "gen_hash_zig": "sha256:bdd1ec462b75bcb51ac79de0aefbf275aa1e9d13c755d5049dc418561c642d49",
   "module": "ast",

.trinity/seals/collections_TriLru.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:947ed3a8df75a4a9ee4c54311c70b9edda1739216d72be28f3cfdaf80958303d",
-  "gen_hash_rust": "sha256:c07ab86a7de321ce47095f951e5bc07bc5d3b3f22fa03822694a65c47a08fc0d",
+  "gen_hash_rust": "sha256:9102ac246ade61f92cd79840980dab11b75512a086a587d32d2fb2081204f174",
   "gen_hash_verilog": "sha256:ebf3050832135b9ec9b6e2480889eabd422468317d7d06e3efa054d06df833cc",
   "gen_hash_zig": "sha256:db41d91af86d45b14de051a11a9259b1534b93caa7e01d2c3c4ca2abe0607f5d",
   "module": "TriLru",
   "ring": 12,
-  "sealed_at": "2026-09-05T02:40:53Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:d42e1ac02e6c07db9accf712b9f83035a8257e7c5c15d691a2da4bdcccc3faf6",
   "spec_path": "specs/tri/collections/lru.t27"

.trinity/seals/collections_TriSet.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:9613b7c8f320bac36af110397bf7b0d1e290b0c2f86783209c1b4f40962784c4",
-  "gen_hash_rust": "sha256:ab38e31fb8d7d8ec8b37ded2cd1ce6718a64f1efa7b51a709ebfe3be9b6a22da",
+  "gen_hash_rust": "sha256:48a66ec67d9eae55810826dd2a5fb14c48a0bb091cd0164d293a7aa8d8da470f",
   "gen_hash_verilog": "sha256:a3f2edcb48986f07d75d8b5ec7e39b7308b6823f508a8bbcf4d84f1cb9d7e6a5",
   "gen_hash_zig": "sha256:3c40e78d01506a92d08946933a7d75abb7a8aabc3bec4df03d9389c19f5a974d",
   "module": "TriSet",
   "ring": 12,
-  "sealed_at": "2026-09-06T02:45:08Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:b4efcdd7ff229ef26b03587176dbb0f75351666de1e6c689597be0322349e3dd",
   "spec_path": "specs/tri/collections/set.t27"

.trinity/seals/compiler_ast.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:fbc813ecf388fc2f9e49d10409608df2cc50cf36339be1b0caf580759b70bc54",
-  "gen_hash_rust": "sha256:cf796b2c39fc159ff964232c2feb3e679f46d71c67f88e4085a41496e131d824",
+  "gen_hash_rust": "sha256:e1895409c636130f9fec6a7b48f812cf1cd8c29bfc99c454f8b7085d53c9058a",
   "gen_hash_verilog": "sha256:13ea818e724f76ac3ef3b457c21d71c31b7b264c3d6c2eee30dc61229eb1eb41",
   "gen_hash_zig": "sha256:bdd1ec462b75bcb51ac79de0aefbf275aa1e9d13c755d5049dc418561c642d49",
   "module": "ast",
   "ring": 12,
-  "sealed_at": "2026-09-06T04:36:41Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:28bfcdf211a0360991fe8d89dc376440d2144b936e030f81e0b5794a1c0eeb00",
   "spec_path": "compiler/ast.t27"

.trinity/seals/encoding_TriHtml.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:1f8b30b7f71c2bcdcdf216fe8dacbf6f68f3e22f9d8f075c289f3c3beb856c45",
-  "gen_hash_rust": "sha256:223e31bf32dcb00bfec3685414e5859a63256c1903d2abf8c47d79c3855d6d59",
+  "gen_hash_rust": "sha256:5120100890657113985b5476a8fc395a72b81a1277b7a1ae9b0ff6bf0f68adb1",
   "gen_hash_verilog": "sha256:1fa7df852949de5a53c7814c90ff93ae0c4849656379383f877f562d98f06fc2",
   "gen_hash_zig": "sha256:c7ed13bb6e091bcedf263a647fa5a434899da8246b96e6427fa04d4797268e7f",
   "module": "TriHtml",
   "ring": 12,
-  "sealed_at": "2026-09-06T05:46:33Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:025959391860663c194a10874f66af7dd8da26f8597f5bee89be66a283a66f60",
   "spec_path": "specs/tri/encoding/html.t27"

.trinity/seals/encoding_TriMsgpack.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:2069e8885ebe9049617e38a4e2d0f2a50f59570bb50cd29ee0981e3b17a96027",
-  "gen_hash_rust": "sha256:300a3d600a5b55835279ca4a4d58056198e8df63d5556596d64d6dad6dd7b235",
+  "gen_hash_rust": "sha256:2fc88453916cd34b97a77f7d030cb60286932edd3ee44893dd3ef29e8a482200",
   "gen_hash_verilog": "sha256:f70c08c4cd1f900cc223d58ee2e550d3b02ad321144a659f3dcc4cb1452be32b",
   "gen_hash_zig": "sha256:04a9c694d50297efa8ed0f1d74eaa7f47b8fe92557e52454ed75a7c885c896c1",
   "module": "TriMsgpack",
   "ring": 12,
-  "sealed_at": "2026-09-05T09:02:10Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:eb6c433fe01f1e6b9fd3a83a79c6575f3e1431b8cccfd78ac6d8db6d0e699eea",
   "spec_path": "specs/tri/encoding/msgpack.t27"

.trinity/seals/encoding_TriXml.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:c13021e282c10254a2f161577c55e506fb096dff8740997d2ff8dbb6a2bf7683",
-  "gen_hash_rust": "sha256:8472efbec7b2f13cd2c5733556cd19a5e5c717a28d81a094cc754bda1341a291",
+  "gen_hash_rust": "sha256:45236f8613780705b2580a7223c49fee5b621b40ac51d878b60ec3dcd6074547",
   "gen_hash_verilog": "sha256:ef20a47e3fc1296bda60734bbe0b8255375a7c35752327385c1b586c354f863b",
   "gen_hash_zig": "sha256:d82f497edfa15ea7da4c2c48aa7abab230377ead54e73c6145ca40a660290c76",
   "module": "TriXml",
   "ring": 12,
-  "sealed_at": "2026-09-06T05:46:33Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:2cd1d3d51078f14f5dd0f53741536884c599975ebb005381d679a5c2542b1000",
   "spec_path": "specs/tri/encoding/xml.t27"

.trinity/seals/graph_TriGraph.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:e211780c0b7bbd8a861e059d0708e5bea52674ead30efcaa1eebcfdd16cf51dc",
-  "gen_hash_rust": "sha256:97397057eab14046c0a4327554771e1b2096e05c6ec590d54fef76268cf9f0b3",
+  "gen_hash_rust": "sha256:a21c1de6323c0a5301195c9b479469b20273ec5e8ffe093ea8863676aacbce1f",
   "gen_hash_verilog": "sha256:c0bd9cddefce72cfb629855f772f6a0d31cf7b538c6132d8a16859dc17becdf7",
   "gen_hash_zig": "sha256:444d15ecc025e0b172fc8594054a13177a0e5496a32390d4261857b5ef804f90",
   "module": "TriGraph",
   "ring": 12,
-  "sealed_at": "2026-09-05T02:40:54Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:121f7a349ba5b7b672b90a9f372f575e9530ef68756c687660ed6ef029278fc5",
   "spec_path": "specs/tri/graph/graph.t27"

.trinity/seals/sdk_contract.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:2a18047c89fb2af3255fe5066f1c35cbba5410cca19598a0fc6c1b0e35ef13a0",
-  "gen_hash_rust": "sha256:28b5de014c24859a2f74e0893707a535295ec8719815f4968bb49098376943e9",
+  "gen_hash_rust": "sha256:8980aeccf629d1dd914cbbd02c717ff0ab08e53b7a72d4c88623c92c04f7c0a9",
   "gen_hash_verilog": "sha256:9bc46f2772e60e074704356e9bb38868a7f263f3cfe251e30a106b82ed41edc3",
   "gen_hash_zig": "sha256:e05074e18d030ac66115f4bd3d65efa2e6a2f76bcd7b27499577d8d47934eb69",
   "module": "sdk_contract",

.trinity/seals/trees_TriTrie.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:dbaea551a83dbeb3302415612fe55402f9f9c24bad77a0abc7903fa5149669ec",
-  "gen_hash_rust": "sha256:57c99ffb2c2dae8b836b14976be847691c2bdc36a4317c045a5e7e0c69e83878",
+  "gen_hash_rust": "sha256:7ce3d8fbeab2e3ebd0653ef061b0444712702bb96063dcad96a8f15d1cc94e26",
   "gen_hash_verilog": "sha256:92be6269928168a86cd2289199bb784ce3383d193966de87fce0e460437de5e9",
   "gen_hash_zig": "sha256:e87caaa2882c44de5510f6e1cbe09afd29ba4443ddc9a7b57a3a6645b3372c43",
   "module": "TriTrie",
   "ring": 12,
-  "sealed_at": "2026-09-05T02:40:54Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:b0439804871b40fdec6d6bd98dfe3f658e7a091e0f7d378d5d9b78999a5335de",
   "spec_path": "specs/tri/trees/trie.t27"

.trinity/seals/zig_codegen.json

@@ -1,6 +1,6 @@
 {
   "gen_hash_c": "sha256:be1cb9a8eb5bb8c80f63aa8db98b7ed69273a0c4e3e09a62d0fc7efec4bd11b5",
-  "gen_hash_rust": "sha256:e15dece9fa8a21f5f634603ef780b497e1bcba0659237d1a6497b8327d78bc1e",
+  "gen_hash_rust": "sha256:2d422d58b346eb22364a64839b0c48fdef43c9f1a57abd9931e324fe06efdfc2",
   "gen_hash_verilog": "sha256:281e5bf4b4bf860712ca54c2b0d173ba6ee0fc6f96043e8c243e9f3e1291a8f1",
   "gen_hash_zig": "sha256:e0de552c5b497d45d640bb9ac9664b1ba515a9d44a2bb280921ffdab5b9fd0f6",
   "module": "zig_codegen",

.trinity/seals/zig_zig_codegen.json

@@ -1,11 +1,11 @@
 {
   "gen_hash_c": "sha256:be1cb9a8eb5bb8c80f63aa8db98b7ed69273a0c4e3e09a62d0fc7efec4bd11b5",
-  "gen_hash_rust": "sha256:e15dece9fa8a21f5f634603ef780b497e1bcba0659237d1a6497b8327d78bc1e",
+  "gen_hash_rust": "sha256:2d422d58b346eb22364a64839b0c48fdef43c9f1a57abd9931e324fe06efdfc2",
   "gen_hash_verilog": "sha256:281e5bf4b4bf860712ca54c2b0d173ba6ee0fc6f96043e8c243e9f3e1291a8f1",
   "gen_hash_zig": "sha256:e0de552c5b497d45d640bb9ac9664b1ba515a9d44a2bb280921ffdab5b9fd0f6",
   "module": "zig_codegen",
   "ring": 12,
-  "sealed_at": "2026-09-06T04:36:41Z",
+  "sealed_at": "2026-09-06T07:17:01Z",
   "sealed_by": "t27c-bootstrap@0.2.0",
   "spec_hash": "sha256:face91b2c4dda278c97006286cdbd18e00e2a2d01e9288eeb0d6520aa47f7fce",
   "spec_path": "compiler/codegen/zig/codegen.t27"

bootstrap/src/compiler.rs

@@ -24612,6 +24612,47 @@ impl RustCodegen {
         })
     }
 
+    /// Split a comma-separated type list, honouring nesting.
+    ///
+    /// A naive `split(',')` cuts `Map<K, V>, T` into `Map<K`, ` V>` and ` T`, which is
+    /// worse than the input. Shared by the tuple arm and the map arm so the two cannot
+    /// disagree about what a comma means.
+    fn split_type_list(inner: &str) -> Option<Vec<String>> {
+        let mut parts: Vec<String> = Vec::new();
+        let (mut depth, mut start) = (0i32, 0usize);
+        for (i, c) in inner.char_indices() {
+            match c {
+                '<' | '[' | '(' => depth += 1,
+                // `->` is a `-` then a `>`, and counting that `>` as a close drove depth
+                // NEGATIVE on `fn(A) -> B`, making the split silently wrong rather than
+                // absent. A list that does not balance is not one this function can answer
+                // about, and None is the honest reply.
+                '>' | ']' | ')' => {
+                    depth -= 1;
+                    if depth < 0 {
+                        return None;
+                    }
+                }
+                ',' if depth == 0 => {
+                    parts.push(inner[start..i].to_string());
+                    start = i + c.len_utf8();
+                }
+                _ => {}
+            }
+        }
+        if depth != 0 {
+            return None;
+        }
+        parts.push(inner[start..].to_string());
+        // An EMPTY argument is not an argument. `std.StringHashMap()` split to one empty
+        // string, passed a `len() == 1` guard and emitted `HashMap<&'static str, >`,
+        // which is not Rust: the guard counted commas where it meant to count types.
+        if parts.iter().any(|q| q.trim().is_empty()) {
+            return None;
+        }
+        Some(parts)
+    }
+
     /// Is this emitted Rust type `Copy`?
     ///
     /// Deliberately a CLOSED list of primitives plus `&'static str` and fixed-size arrays
@@ -24651,6 +24692,56 @@ impl RustCodegen {
             (t, false)
         };
 
+        // A Zig standard-library MAP, which eight corpus fields declare as their type:
+        //
+        //     "std.StringHashMap([]const u8)"      5 fields
+        //     "std.HashMap(K, V)"                  3 fields
+        //
+        // The type is written as a QUOTED STRING in the spec; the compiler strips the
+        // quotes and emits the content, so rustc received `std.StringHashMap(...)`, which
+        // is not Rust. `StringHashMap` keys by string, so its Rust equivalent names the
+        // key type the Zig form leaves implicit.
+        //
+        // Anchored on the WHOLE type string. `std.math.`, `std.mem.` and the rest appear
+        // only in expression position and never reach this function, but an unanchored
+        // match would be a rule about a prefix rather than about a type.
+        if let Some(rest) = base_type.strip_prefix("std.StringHashMap(") {
+            if let Some(v) = rest.strip_suffix(')') {
+                // ARITY. `StringHashMap` takes exactly one argument; without this guard
+                // `std.StringHashMap(K, V)` emitted `HashMap<String, K, V>` -- three type
+                // arguments, which is not Rust. A wrong arity now falls through to the
+                // default and rustc says so loudly, which is the honest outcome.
+                let args = Self::split_type_list(v).unwrap_or_default();
+                if args.len() == 1 {
+                    // The KEY type is whatever this emitter maps `[]const u8` to, not a
+                    // hardcoded `String`. Zig's `StringHashMap` keys by `[]const u8`, and
+                    // writing `String` here made two spellings of the same intent produce
+                    // incompatible Rust: `std.StringHashMap(u32)` gave
+                    // `HashMap<String, u32>` while `std.HashMap([]const u8, u32)` gave
+                    // `HashMap<&'static str, u32>`. One emitter, one answer.
+                    let key = Self::t27_type_to_rust("[]const u8");
+                    let out = format!(
+                        "std::collections::HashMap<{key}, {}>",
+                        Self::t27_type_to_rust(args[0].trim())
+                    );
+                    return if is_optional { format!("Option<{out}>") } else { out };
+                }
+            }
+        }
+        if let Some(rest) = base_type.strip_prefix("std.HashMap(") {
+            if let Some(kv) = rest.strip_suffix(')') {
+                let parts = Self::split_type_list(kv).unwrap_or_default();
+                if parts.len() == 2 {
+                    let out = format!(
+                        "std::collections::HashMap<{}, {}>",
+                        Self::t27_type_to_rust(parts[0].trim()),
+                        Self::t27_type_to_rust(parts[1].trim())
+                    );
+                    return if is_optional { format!("Option<{out}>") } else { out };
+                }
+            }
+        }
+
         // A TUPLE maps element by element. Without this arm `(A, B)` fell through to
         // the default and was emitted verbatim, so an inner `[]f32` -- which every other
         // position maps to `Vec<f32>` -- reached rustc as `[]f32`. The rule existed and
@@ -24660,20 +24751,18 @@ impl RustCodegen {
         // `Map<K` and ` V>` and produce something worse than the input.
         if base_type.starts_with('(') && base_type.ends_with(')') && base_type.len() > 2 {
             let inner = &base_type[1..base_type.len() - 1];
-            let mut parts: Vec<String> = Vec::new();
-            let (mut depth, mut start) = (0i32, 0usize);
-            for (i, c) in inner.char_indices() {
-                match c {
-                    '<' | '[' | '(' => depth += 1,
-                    '>' | ']' | ')' => depth -= 1,
-                    ',' if depth == 0 => {
-                        parts.push(inner[start..i].to_string());
-                        start = i + c.len_utf8();
+            let parts = match Self::split_type_list(inner) {
+                Some(p) => p,
+                // Malformed inside a tuple: leave it exactly as written, which is what
+                // this position did before the arm existed. rustc then says so loudly.
+                None => {
+                    return if is_optional {
+                        format!("Option<{base_type}>")
+                    } else {
+                        base_type.to_string()
                     }
-                    _ => {}
                 }
-            }
-            parts.push(inner[start..].to_string());
+            };
             // A one-element "tuple" is a parenthesised type, not a tuple, and Rust writes
             // it without the comma. Emitting `(T,)` there would change the type.
             let mapped: Vec<String> = parts

bootstrap/stage0/FROZEN_HASH

@@ -1 +1 @@
-23f03e8a97d5588d06cdb84d3e59baa03c5474d9a28ef361f9bc26bd9b72f6d1 bootstrap/src/compiler.rs
+5b05ef6357a7139dbc16bd60977eda9294eecb01f9d2d3be58c8816796e418cc bootstrap/src/compiler.rs