Support signed numeric constants in match pattern ASTs (#9279)

Recognize numeric Expr::Constant values when validating signed literal
patterns, alongside parser-produced NumberLiteral nodes. Python AST
conversion uses the former representation. Accept unary plus as well as
minus and fold signed real/imaginary and complex patterns consistently.

Boolean and non-numeric constants remain excluded. Preserve the existing
parser-produced literal path and do not change source grammar.

Assisted-by: OpenAI Codex:model-version-unavailable

crates/codegen/src/compile.rs

@@ -12288,12 +12288,12 @@ impl<'warnings> Compiler<'warnings> {
         &mut self,
         expr: &ast::Expr,
     ) -> CompileResult<Option<ConstantData>> {
-        // CPython 3.14 ast_preprocess.c::fold_const_match_patterns()
+        // CPython ast_preprocess.c::fold_const_match_patterns()
         // folds only the constant forms needed by match patterns before
         // codegen_pattern_value()/codegen_pattern_mapping_key() visit them.
         Ok(match expr {
             ast::Expr::UnaryOp(ast::ExprUnaryOp {
-                op: ast::UnaryOp::USub,
+                op: op @ (ast::UnaryOp::UAdd | ast::UnaryOp::USub),
                 operand,
                 ..
             }) => {
@@ -12301,7 +12301,11 @@ impl<'warnings> Compiler<'warnings> {
                 else {
                     return Ok(None);
                 };
-                Self::try_negate_match_pattern_constant(constant)
+                if *op == ast::UnaryOp::USub {
+                    Self::try_negate_match_pattern_constant(constant)
+                } else {
+                    Some(constant)
+                }
             }
             ast::Expr::BinOp(ast::ExprBinOp {
                 left, op, right, ..
@@ -12326,7 +12330,7 @@ impl<'warnings> Compiler<'warnings> {
             return Ok(Some(constant));
         }
         let ast::Expr::UnaryOp(ast::ExprUnaryOp {
-            op: ast::UnaryOp::USub,
+            op: op @ (ast::UnaryOp::UAdd | ast::UnaryOp::USub),
             operand,
             ..
         }) = expr
@@ -12336,7 +12340,11 @@ impl<'warnings> Compiler<'warnings> {
         let Some(constant) = self.try_compile_match_pattern_real_constant(operand)? else {
             return Ok(None);
         };
-        Ok(Self::try_negate_match_pattern_constant(constant))
+        Ok(if *op == ast::UnaryOp::USub {
+            Self::try_negate_match_pattern_constant(constant)
+        } else {
+            Some(constant)
+        })
     }
 
     fn try_compile_match_pattern_real_constant(

crates/vm/src/stdlib/_ast/validate.rs

@@ -191,6 +191,13 @@ fn validate_interpolated_elements<'a>(
 }
 
 fn ensure_literal_number(expr: &ast::Expr, allow_real: bool, allow_imaginary: bool) -> bool {
+    if let Some(constant) = ast_constant_value(expr) {
+        return match constant {
+            ConstantData::Integer { .. } | ConstantData::Float { .. } => allow_real,
+            ConstantData::Complex { .. } => allow_imaginary,
+            _ => false,
+        };
+    }
     let ast::Expr::NumberLiteral(number) = expr else {
         return false;
     };
@@ -200,11 +207,11 @@ fn ensure_literal_number(expr: &ast::Expr, allow_real: bool, allow_imaginary: bo
     }
 }
 
-fn ensure_literal_negative(expr: &ast::Expr, allow_real: bool, allow_imaginary: bool) -> bool {
+fn ensure_literal_signed(expr: &ast::Expr, allow_real: bool, allow_imaginary: bool) -> bool {
     let ast::Expr::UnaryOp(unary) = expr else {
         return false;
     };
-    if unary.op != ast::UnaryOp::USub {
+    if !matches!(unary.op, ast::UnaryOp::UAdd | ast::UnaryOp::USub) {
         return false;
     }
     ensure_literal_number(&unary.operand, allow_real, allow_imaginary)
@@ -218,7 +225,7 @@ fn ensure_literal_complex(expr: &ast::Expr) -> bool {
         return false;
     }
     let real_left = ensure_literal_number(&bin.left, true, false)
-        || ensure_literal_negative(&bin.left, true, false);
+        || ensure_literal_signed(&bin.left, true, false);
     real_left && ensure_literal_number(&bin.right, false, true)
 }
 
@@ -244,7 +251,7 @@ fn validate_pattern_match_value(vm: &VirtualMachine, expr: &ast::Expr) -> PyResu
             Ok(())
         }
         ast::Expr::Attribute(_) => Ok(()),
-        ast::Expr::UnaryOp(_) if ensure_literal_negative(expr, true, true) => Ok(()),
+        ast::Expr::UnaryOp(_) if ensure_literal_signed(expr, true, true) => Ok(()),
         ast::Expr::BinOp(_) if ensure_literal_complex(expr) => Ok(()),
         ast::Expr::FString(_) | ast::Expr::TString(_) => Ok(()),
         ast::Expr::BooleanLiteral(_)