refactor(surface): share the copy-pasted parser sub-productions

Round-trip-preserving — the byte-isomorphic Form-A ↔ JSON-AST tests,
the hash pins, and the full fixture-corpus parse are all green; error
strings passed through verbatim, not homogenised.

- The Int/Float/Str/true/false literal-token match was inlined in three
  parsers; extracted try_parse_literal_token and routed parse_pat_lit
  and the parse_term fallthrough through it.
- parse_doc and parse_export were identical but for the keyword; both
  now go through one parse_string_attr, and the previously
  doc/export-bypassed expect_string helper is back on the shared path.
- parse_effects_clause and parse_forall_constraints_clause shared the
  expect-keyword / collect / reject-empty / expect-rparen shape;
  unified under parse_repeating_clause, with each clause's empty-error
  message passed in.

parse_intrinsic_attr was left inline-able-but-not-inlined: it has two
call sites, so inlining would re-duplicate a documented helper.

crates/ailang-surface/src/parse.rs

@@ -505,54 +505,29 @@ impl<'a> Parser<'a> {
         })
     }
 
-    fn parse_doc(&mut self) -> Result<String, ParseError> {
-        self.expect_lparen("doc-attr")?;
-        self.expect_keyword("doc")?;
-        let s = match self.peek().cloned() {
-            Some(Token { tok: Tok::Str(s), .. }) => {
-                self.cur += 1;
-                s
-            }
-            Some(t) => {
-                return Err(ParseError::Unexpected {
-                    expected: "string literal (doc body)".into(),
-                    got: tok_label(&t.tok),
-                    pos: t.span.start,
-                });
-            }
-            None => {
-                return Err(ParseError::UnexpectedEof {
-                    expected: "string literal (doc body)".into(),
-                });
-            }
-        };
-        self.expect_rparen("doc-attr")?;
+    /// Parse a `(<kw> "<string>")` attribute clause into its string
+    /// payload. `prod` is the production tag used for the paren-balance
+    /// diagnostics; `body_ctx` parameterises the string-literal error
+    /// (e.g. `"doc body"`, `"export C symbol"`).
+    fn parse_string_attr(
+        &mut self,
+        prod: &'static str,
+        kw: &'static str,
+        body_ctx: &'static str,
+    ) -> Result<String, ParseError> {
+        self.expect_lparen(prod)?;
+        self.expect_keyword(kw)?;
+        let s = self.expect_string(body_ctx)?;
+        self.expect_rparen(prod)?;
         Ok(s)
     }
 
+    fn parse_doc(&mut self) -> Result<String, ParseError> {
+        self.parse_string_attr("doc-attr", "doc", "doc body")
+    }
+
     fn parse_export(&mut self) -> Result<String, ParseError> {
-        self.expect_lparen("export-attr")?;
-        self.expect_keyword("export")?;
-        let s = match self.peek().cloned() {
-            Some(Token { tok: Tok::Str(s), .. }) => {
-                self.cur += 1;
-                s
-            }
-            Some(t) => {
-                return Err(ParseError::Unexpected {
-                    expected: "string literal (export C symbol)".into(),
-                    got: tok_label(&t.tok),
-                    pos: t.span.start,
-                });
-            }
-            None => {
-                return Err(ParseError::UnexpectedEof {
-                    expected: "string literal (export C symbol)".into(),
-                });
-            }
-        };
-        self.expect_rparen("export-attr")?;
-        Ok(s)
+        self.parse_string_attr("export-attr", "export", "export C symbol")
     }
 
     fn parse_ctor(&mut self) -> Result<Ctor, ParseError> {
@@ -713,8 +688,9 @@ impl<'a> Parser<'a> {
         Ok(Suppress { code, because })
     }
 
-    /// helper — consume one string-literal token. Used by
-    /// [`Self::parse_suppress_attr`].
+    /// helper — consume one string-literal token. Shared by
+    /// [`Self::parse_string_attr`] (doc / export bodies) and
+    /// [`Self::parse_suppress_attr`] (code / because bodies).
     fn expect_string(&mut self, ctx: &'static str) -> Result<String, ParseError> {
         match self.peek().cloned() {
             Some(Token { tok: Tok::Str(s), .. }) => {
@@ -1217,27 +1193,46 @@ impl<'a> Parser<'a> {
         })
     }
 
-    fn parse_effects_clause(&mut self) -> Result<Vec<String>, ParseError> {
-        self.expect_lparen("effects-clause")?;
-        self.expect_keyword("effects")?;
-        // 1+ idents per grammar; round-trip allows empty too (to support
-        // any future use), but the printer never emits an empty clause.
+    /// Parse a `(<kw> item+)` clause requiring at least one item. The
+    /// `item` parser is applied repeatedly until the closing paren; an
+    /// empty body fails with `empty_msg` (a per-clause string so the
+    /// diagnostic stays specific). `prod` tags the paren-balance errors.
+    fn parse_repeating_clause<T>(
+        &mut self,
+        prod: &'static str,
+        kw: &'static str,
+        empty_msg: &'static str,
+        item: fn(&mut Self) -> Result<T, ParseError>,
+    ) -> Result<Vec<T>, ParseError> {
+        self.expect_lparen(prod)?;
+        self.expect_keyword(kw)?;
         let mut out = Vec::new();
         while !matches!(self.peek(), Some(Token { tok: Tok::RParen, .. })) {
-            out.push(self.expect_ident("effect name")?);
+            out.push(item(self)?);
         }
         if out.is_empty() {
             let pos = self.peek().map(|t| t.span.start).unwrap_or(0);
             return Err(ParseError::Production {
-                production: "effects-clause",
-                message: "expected at least one effect name".into(),
+                production: prod,
+                message: empty_msg.into(),
                 pos,
             });
         }
-        self.expect_rparen("effects-clause")?;
+        self.expect_rparen(prod)?;
         Ok(out)
     }
 
+    fn parse_effects_clause(&mut self) -> Result<Vec<String>, ParseError> {
+        // 1+ idents per grammar; round-trip allows empty too (to support
+        // any future use), but the printer never emits an empty clause.
+        self.parse_repeating_clause(
+            "effects-clause",
+            "effects",
+            "expected at least one effect name",
+            |p| p.expect_ident("effect name"),
+        )
+    }
+
     fn parse_forall_type(&mut self) -> Result<Type, ParseError> {
         self.expect_lparen("forall-type")?;
         self.expect_keyword("forall")?;
@@ -1267,22 +1262,12 @@ impl<'a> Parser<'a> {
     }
 
     fn parse_forall_constraints_clause(&mut self) -> Result<Vec<Constraint>, ParseError> {
-        self.expect_lparen("forall.constraints")?;
-        self.expect_keyword("constraints")?;
-        let mut out = Vec::new();
-        while !matches!(self.peek(), Some(Token { tok: Tok::RParen, .. })) {
-            out.push(self.parse_constraint()?);
-        }
-        if out.is_empty() {
-            let pos = self.peek().map(|t| t.span.start).unwrap_or(0);
-            return Err(ParseError::Production {
-                production: "forall.constraints",
-                message: "(constraints …) clause must contain at least one (constraint …)".into(),
-                pos,
-            });
-        }
-        self.expect_rparen("forall.constraints")?;
-        Ok(out)
+        self.parse_repeating_clause(
+            "forall.constraints",
+            "constraints",
+            "(constraints …) clause must contain at least one (constraint …)",
+            |p| p.parse_constraint(),
+        )
     }
 
     fn parse_constraint(&mut self) -> Result<Constraint, ParseError> {
@@ -1340,36 +1325,27 @@ impl<'a> Parser<'a> {
                     }
                 }
             }
-            Some(Token { tok: Tok::Ident(s), .. }) => {
-                self.cur += 1;
-                if s == "true" {
-                    Ok(Term::Lit { lit: Literal::Bool { value: true } })
-                } else if s == "false" {
-                    Ok(Term::Lit { lit: Literal::Bool { value: false } })
-                } else {
-                    Ok(Term::Var { name: s })
+            _ => {
+                if let Some(lit) = self.try_parse_literal_token() {
+                    return Ok(Term::Lit { lit });
+                }
+                match self.peek().cloned() {
+                    // A non-boolean ident is a variable reference, not a
+                    // literal — `try_parse_literal_token` left it for us.
+                    Some(Token { tok: Tok::Ident(s), .. }) => {
+                        self.cur += 1;
+                        Ok(Term::Var { name: s })
+                    }
+                    Some(t) => Err(ParseError::Unexpected {
+                        expected: "term".into(),
+                        got: tok_label(&t.tok),
+                        pos: t.span.start,
+                    }),
+                    None => Err(ParseError::UnexpectedEof {
+                        expected: "term".into(),
+                    }),
                 }
             }
-            Some(Token { tok: Tok::Int(v), .. }) => {
-                self.cur += 1;
-                Ok(Term::Lit { lit: Literal::Int { value: v } })
-            }
-            Some(Token { tok: Tok::Float(bits), .. }) => {
-                self.cur += 1;
-                Ok(Term::Lit { lit: Literal::Float { bits } })
-            }
-            Some(Token { tok: Tok::Str(s), .. }) => {
-                self.cur += 1;
-                Ok(Term::Lit { lit: Literal::Str { value: s } })
-            }
-            Some(t) => Err(ParseError::Unexpected {
-                expected: "term".into(),
-                got: tok_label(&t.tok),
-                pos: t.span.start,
-            }),
-            None => Err(ParseError::UnexpectedEof {
-                expected: "term".into(),
-            }),
         }
     }
 
@@ -1879,49 +1855,44 @@ impl<'a> Parser<'a> {
         Ok(Pattern::Ctor { ctor, fields })
     }
 
+    /// Consume one literal-form token — an `Int`, `Float`, `Str`, or the
+    /// idents `true` / `false` — and return its [`Literal`]. Any other
+    /// token (including a non-boolean ident) leaves the cursor untouched
+    /// and returns `None`, so each caller decides how to handle the
+    /// non-literal fallthrough (a bare ident is `Term::Var` in a term but
+    /// an error in a `pat-lit`).
+    fn try_parse_literal_token(&mut self) -> Option<Literal> {
+        let lit = match &self.peek()?.tok {
+            Tok::Int(v) => Literal::Int { value: *v },
+            Tok::Float(bits) => Literal::Float { bits: *bits },
+            Tok::Str(s) => Literal::Str { value: s.clone() },
+            Tok::Ident(s) if s == "true" => Literal::Bool { value: true },
+            Tok::Ident(s) if s == "false" => Literal::Bool { value: false },
+            _ => return None,
+        };
+        self.cur += 1;
+        Some(lit)
+    }
+
     fn parse_pat_lit(&mut self) -> Result<Pattern, ParseError> {
         self.expect_lparen("pat-lit")?;
         self.expect_keyword("pat-lit")?;
-        let lit = match self.peek().cloned() {
-            Some(Token { tok: Tok::Int(v), .. }) => {
-                self.cur += 1;
-                Literal::Int { value: v }
-            }
-            Some(Token { tok: Tok::Float(bits), .. }) => {
-                self.cur += 1;
-                Literal::Float { bits }
-            }
-            Some(Token { tok: Tok::Str(s), .. }) => {
-                self.cur += 1;
-                Literal::Str { value: s }
-            }
-            Some(Token { tok: Tok::Ident(s), span }) => {
-                if s == "true" {
-                    self.cur += 1;
-                    Literal::Bool { value: true }
-                } else if s == "false" {
-                    self.cur += 1;
-                    Literal::Bool { value: false }
-                } else {
+        let lit = match self.try_parse_literal_token() {
+            Some(lit) => lit,
+            None => match self.peek() {
+                Some(t) => {
                     return Err(ParseError::Unexpected {
                         expected: "literal form (integer, float, string, `true`, or `false`)".into(),
-                        got: tok_label(&Tok::Ident(s)),
-                        pos: span.start,
+                        got: tok_label(&t.tok),
+                        pos: t.span.start,
                     });
                 }
-            }
-            Some(t) => {
-                return Err(ParseError::Unexpected {
-                    expected: "literal form (integer, float, string, `true`, or `false`)".into(),
-                    got: tok_label(&t.tok),
-                    pos: t.span.start,
-                });
-            }
-            None => {
-                return Err(ParseError::UnexpectedEof {
-                    expected: "literal form".into(),
-                });
-            }
+                None => {
+                    return Err(ParseError::UnexpectedEof {
+                        expected: "literal form".into(),
+                    });
+                }
+            },
         };
         self.expect_rparen("pat-lit")?;
         Ok(Pattern::Lit { lit })