Merge admission: eliminate the five first() record-field assignments and the parse_int argument site

dag/gunbc/merge_admission_produce.dag

@@ -96,8 +96,12 @@ fn receipt_wire_v2_pr_number(lines: List<String>) -> ReceiptWirePrNumber {
   if length(lines) == 6 {
     WirePrAbsent
   } else {
-    match parse_int(s: lines.skip(n: 6).first()) {
-      Present { value: n } => WirePrPresent { value: n }
+    match lines.skip(n: 6).first() {
+      Present { value: pr_line } =>
+        match parse_int(s: pr_line) {
+          Present { value: n } => WirePrPresent { value: n }
+          Absent => WirePrMalformed
+        }
       Absent => WirePrMalformed
     }
   }
@@ -125,29 +129,37 @@ fn parse_receipt_wire_v2(text: String) -> MergeAdmissionReceiptV2? {
                 match parse_gate_roster_hash_wire(line: lines.skip(n: 2).first()) {
                   Absent => none
                   Present { value: gate_roster_hash } =>
-                    match receipt_wire_v2_pr_number(lines: lines) {
-                      WirePrMalformed => none
-                      WirePrAbsent =>
-                        Present {
-                          value: MergeAdmissionReceiptV2 {
-                            attempt_id: attempt,
-                            pr_number: none,
-                            tested_head_sha: lines.skip(n: 4).first(),
-                            tested_base_commit_sha: lines.skip(n: 5).first(),
-                            gate_roster_hash: gate_roster_hash,
-                            conclusion: conclusion,
-                          }
-                        }
-                      WirePrPresent { value: n } =>
-                        Present {
-                          value: MergeAdmissionReceiptV2 {
-                            attempt_id: attempt,
-                            pr_number: Present { value: n },
-                            tested_head_sha: lines.skip(n: 4).first(),
-                            tested_base_commit_sha: lines.skip(n: 5).first(),
-                            gate_roster_hash: gate_roster_hash,
-                            conclusion: conclusion,
-                          }
+                    match lines.skip(n: 4).first() {
+                      Absent => none
+                      Present { value: head_line } =>
+                        match lines.skip(n: 5).first() {
+                          Absent => none
+                          Present { value: base_commit_line } =>
+                            match receipt_wire_v2_pr_number(lines: lines) {
+                              WirePrMalformed => none
+                              WirePrAbsent =>
+                                Present {
+                                  value: MergeAdmissionReceiptV2 {
+                                    attempt_id: attempt,
+                                    pr_number: none,
+                                    tested_head_sha: head_line,
+                                    tested_base_commit_sha: base_commit_line,
+                                    gate_roster_hash: gate_roster_hash,
+                                    conclusion: conclusion,
+                                  }
+                                }
+                              WirePrPresent { value: n } =>
+                                Present {
+                                  value: MergeAdmissionReceiptV2 {
+                                    attempt_id: attempt,
+                                    pr_number: Present { value: n },
+                                    tested_head_sha: head_line,
+                                    tested_base_commit_sha: base_commit_line,
+                                    gate_roster_hash: gate_roster_hash,
+                                    conclusion: conclusion,
+                                  }
+                                }
+                            }
                         }
                     }
                 }

dag/gunbc/merge_admission_subject.dag

@@ -171,14 +171,26 @@ fn parse_tested_subject_wire(text: String) -> TestedSubject? {
   } else {
     match walk_attempt_id(raw: lines.skip(n: 1).first()) {
       Absent => none
-      Present { value: attempt } => Present {
-        value: TestedSubject {
-          attempt_id: attempt,
-          base_ref: lines.skip(n: 2).first(),
-          head_sha: lines.skip(n: 3).first(),
-          base_commit_sha: lines.skip(n: 4).first(),
+      Present { value: attempt } =>
+        match lines.skip(n: 2).first() {
+          Absent => none
+          Present { value: base_ref_line } =>
+            match lines.skip(n: 3).first() {
+              Absent => none
+              Present { value: head_line } =>
+                match lines.skip(n: 4).first() {
+                  Absent => none
+                  Present { value: base_commit_line } => Present {
+                    value: TestedSubject {
+                      attempt_id: attempt,
+                      base_ref: base_ref_line,
+                      head_sha: head_line,
+                      base_commit_sha: base_commit_line,
+                    }
+                  }
+                }
+            }
         }
-      }
     }
   }
 }

dag/test/claim/merge_admission_attempt_witness_test.dag

@@ -607,17 +607,30 @@ fn v2_refuses(text: String) -> Bool {
   match parse_receipt_wire_v2(text: text) { Present { value: _ } => false  Absent => true }
 }
 
-// Positive control: the same builder with every line correct MUST parse, or every row below is
-// satisfied by a wire that was malformed for some other reason.
-test fn wire_v2_built_from_explicit_lines_parses() -> Bool {
+// Positive control, asserted at CARRIER GRAIN rather than on the verdict. A parser that returns
+// `Present` before and after a rewrite while binding a different head SHA, attempt id, base commit
+// or roster hash is NOT a no-op, and a `Present { value: _ } => true` row cannot see that. Every
+// field the accepted class carries is asserted, so a rewrite that reads the wrong line -- an
+// off-by-one in a `skip`, a field crossed with its neighbour -- goes red here rather than passing
+// as an unchanged verdict.
+test fn wire_v2_built_from_explicit_lines_parses_with_every_field_bound() -> Bool {
   match parse_receipt_wire_v2(text: wire_v2_with_lines(
     schema: merge_admission_receipt_schema_v2,
     attempt: attempt_a_raw,
     roster: render_gate_roster_hash_wire(hash: roster_fx()),
     conclusion: good_v2_lines_conclusion(),
     head: head_sha_fx,
     base: base_commit_fx,
-  )) { Present { value: _ } => true  Absent => false }
+  )) {
+    Present { value: parsed } =>
+      ((parsed.attempt_id as String) == attempt_a_raw)
+        && (parsed.tested_head_sha == head_sha_fx)
+        && (parsed.tested_base_commit_sha == base_commit_fx)
+        && (parsed.gate_roster_hash == roster_fx())
+        && match parsed.pr_number { Absent => true  Present { value: _ } => false }
+        && match parsed.conclusion { Success => true  _ => false }
+    Absent => false
+  }
 }
 
 test fn wire_v2_refuses_a_wrong_schema_line() -> Bool {
@@ -671,14 +684,14 @@ test fn wire_v2_refuses_a_blank_base_commit_line() -> Bool {
 // same defect one parser over from the one the mutation control caught.
 test fn object_id_wire_accepts_a_valid_sha1_wire() -> Bool {
   match parse_git_object_id_wire(raw: "sha1:abc1234def5678901234567890abcd1234567890") {
-    Present { value: _ } => true
+    Present { value: oid } => git_object_id_wire_hex(oid: oid) == "abc1234def5678901234567890abcd1234567890"
     Absent => false
   }
 }
 
 test fn object_id_wire_accepts_a_valid_sha256_wire() -> Bool {
   match parse_git_object_id_wire(raw: "sha256:abc1234def5678901234567890abcd12abc1234def5678901234567890abcd12") {
-    Present { value: _ } => true
+    Present { value: oid } => git_object_id_wire_hex(oid: oid) == "abc1234def5678901234567890abcd12abc1234def5678901234567890abcd12"
     Absent => false
   }
 }
@@ -704,16 +717,24 @@ fn subject_refuses(text: String) -> Bool {
   match parse_tested_subject_wire(text: text) { Present { value: _ } => false  Absent => true }
 }
 
-// Positive control for the builder, without which every refusal row below could be satisfied by a
-// wire malformed for some other reason.
-test fn subject_wire_built_from_explicit_lines_parses() -> Bool {
+// Positive control for the builder, at carrier grain for the same reason as the receipt one above:
+// `base_ref`, `head_sha` and `base_commit_sha` are three consecutive lines, so a rewrite that reads
+// the wrong one keeps the verdict and changes the value.
+test fn subject_wire_built_from_explicit_lines_parses_with_every_field_bound() -> Bool {
   match parse_tested_subject_wire(text: subject_wire_with_lines(
     schema: merge_admission_tested_subject_schema,
     attempt: attempt_a_raw,
     base_ref: "origin/main",
     head: head_sha_fx,
     base_commit: base_commit_fx,
-  )) { Present { value: _ } => true  Absent => false }
+  )) {
+    Present { value: parsed } =>
+      ((parsed.attempt_id as String) == attempt_a_raw)
+        && (parsed.base_ref == "origin/main")
+        && (parsed.head_sha == head_sha_fx)
+        && (parsed.base_commit_sha == base_commit_fx)
+    Absent => false
+  }
 }
 
 test fn subject_wire_refuses_a_wrong_schema_line() -> Bool {