feat!: Explicit Project outputs

API.md

@@ -36,7 +36,7 @@ Functions:
   ## 10 @  1: add
 
 === Plan
-Project[$0, $1, add($0, $1):i32?]
+Project[_ => $0, $1, add($0, $1):i32?]
   Read[table1 => col1:i32?, col2:i32?]
 "#;
 
@@ -59,7 +59,7 @@ use substrait_explain::{parse, format_with_options, OutputOptions, Visibility};
 
 let plan = parse(r#"
 === Plan
-Project[$0, 42, 54:i16]
+Project[_ => $0, 42, 54:i16]
   Read[data => name:string?, num:i64]
 "#).unwrap();
 
@@ -244,7 +244,7 @@ Functions:
 === Plan
 Root[result]
   Aggregate[$0 => $0, sum($1):i32?, count($1):i64]
-    Project[$0, add($1, $2):i32?]
+    Project[_ => $0, add($1, $2):i32?]
       Read[table1 => category:string, col1:i32?, col2:i32?]
 ```
 

GRAMMAR.md

@@ -81,7 +81,7 @@ Functions:
 
 === Plan
 Root[result]
-  Project[$0, $1, add($0, $1):i64]
+  Project[_ => $0, $1, add($0, $1):i64]
     Read[orders => quantity:i32?, price:i64]
 # "#;
 #
@@ -178,7 +178,7 @@ Functions:
 
 === Plan
 Root[result]                   // Level 0 (no indentation)
-  Project[$0, $1]              // Level 1 (2 spaces)
+  Project[_ => $0, $1]              // Level 1 (2 spaces)
     Filter[gt($0, 10):boolean => $0]   // Level 2 (4 spaces)
       Read[data => a:i64]      // Level 3 (6 spaces)
 # "#;
@@ -298,7 +298,7 @@ From [official Substrait grammar](https://raw.githubusercontent.com/substrait-io
 let plan_text = r#"
 === Plan
 Root[result]
-  Project[$0, $1, $2, $3]
+  Project[_ => $0, $1, $2, $3]
     Read[data => int_field:i64, string_field:string?, created_at:timestamp?, user_id:uuid]
 "#;
 #
@@ -360,7 +360,7 @@ use substrait_explain::Parser;
 let plan_text = r#"
 === Plan
 Root[result]
-  Project[$0, $1, $2]
+  Project[_ => $0, $1, $2]
     Read[data => list_field:list<i64>, map_field:map<string, i64>, struct_field:struct<i64, string?>]
 "#;
 
@@ -400,7 +400,7 @@ Functions:
 
 === Plan
 Root[result]
-  Project[$0, $1, $2]
+  Project[_ => $0, $1, $2]
     Read[data => point_field:point#8@1?<i8>, custom_field:custom_type#9, prefixed_field:u!custom_type]
 # "#;
 #
@@ -437,7 +437,7 @@ Currently, only references to fields in the Relations' input are supported.
 # let plan_text = r#"
 === Plan
 Root[result]
-  Project[$0, $1, $42]
+  Project[_ => $0, $1, $42]
     Read[data => field0:i64, field1:string, field42:boolean]
 # "#;
 #
@@ -523,7 +523,7 @@ An IfThen expression is a conditional function or logical operator that evaluate
 === Plan
 Root[status]
   Fetch[limit=10, offset=0 => $0]
-    Project[if_then(true -> $0, false -> $1, _ -> $2)]
+    Project[_ => if_then(true -> $0, false -> $1, _ -> $2)]
       Read[events.logs => status:string?]
 #  "#;
 #
@@ -689,7 +689,7 @@ form a 1-element tuple: `(x,)`. For 2+ elements the trailing comma is optional:
 # let plan_text = r#"
 === Plan
 Root[c, d]           // root with output columns c and d
-  Project[$0, $1]
+  Project[_ => $0, $1]
     Read[data => a:i64, b:string]
 # "#;
 #
@@ -984,7 +984,7 @@ Functions:
 === Plan
 Root[result]
   Filter[gt($2, 100):boolean => $0, $1, $2]
-    Project[$0, $1, $2]
+    Project[_ => $0, $1, $2]
       Read[data => a:i64, b:string, c:i32]
 # "#;
 #
@@ -996,11 +996,18 @@ Root[result]
 
 #### Syntax
 
-`"Project" "[" (expression ("," expression)*)? "]"`
+```text
+project_relation := "Project" "[" "_" project_output? "]"
+project_output   := "=>" project_values
+                  / "+>" project_additions ("|>" emit_mapping)?
+```
 
 #### Components
 
-- `expression` - field reference, function call, or literal (see Expressions section)
+- The leading `_` is Project's required empty parameter list.
+- `project_values` is a comma-separated list of input references and expressions. In compact `=>` syntax, it describes Project's final output.
+- `project_additions` is a comma-separated list of expressions appended to Project's inherited input fields. Use `_` when it is empty.
+- `emit_mapping` references the complete direct output: inherited input fields first, followed by `project_additions`.
 
 #### Example
 
@@ -1010,7 +1017,7 @@ Root[result]
 # let plan_text = r#"
 === Plan
 Root[result]
-  Project[$1, 42]                    // project field 1 and literal 42
+  Project[_ => $1, 42]               // project field 1 and literal 42
     Read[data => a:i64, b:string]
 # "#;
 #
@@ -1440,7 +1447,7 @@ Functions:
 Root[customer_revenue]
   Aggregate[$0, $1 => $0, $1, sum($3):i64]
     Filter[gt($3, 100):boolean => $0, $1, $2, $3]
-      Project[$0, $1, $2, multiply($4, $5):i64]
+      Project[_ => $0, $1, $2, multiply($4, $5):i64]
         Join[&Inner, eq($0, $3):boolean => $0, $1, $2, $3, $4, $5]
           Read[users => id:i64, name:string, region:string]
           Read[orders => user_id:i64, quantity:i32, price:i64]

README.md

@@ -103,7 +103,7 @@ Functions:
 === Plan
 Root[revenue]
   Filter[gt($2, 100) => $0, $1]
-    Project[$0, $1, multiply($0, $1)]
+    Project[_ => $0, $1, multiply($0, $1)]
       Read[orders => quantity:i32?, price:fp64?]
 ```
 
@@ -157,7 +157,7 @@ Functions:
 === Plan
 Root[revenue]
   Filter[gt($2, 100) => $0, $1]
-    Project[$0, $1, multiply($0, $1)]
+    Project[_ => $0, $1, multiply($0, $1)]
       Read[orders => quantity:i32?, price:fp64?]
 "#;
 

example-plans/basic.substrait

@@ -1,4 +1,4 @@
 === Plan
 Root[result]
-  Project[$0, $1]
+  Project[_ => $0, $1]
     Read[data => a:i64, b:string]

example-plans/simple.substrait

@@ -13,15 +13,15 @@ Functions:
 === Plan
 Root[c, d]
   Filter[eq($0, 0):boolean => $0, $1]
-    Project[$1, abs($0):fp64?]
+    Project[_ => $1, abs($0):fp64?]
       Read[schema.table => a:fp64?, b:i64]
 
 Root[c, d, e]
   Aggregate[$0 => $0, sum($1):fp64?, count($1):i64]
     Read[schema.table => name:string?, num:fp64?, id:i64]
 
 Root[name, num]
-  Project[$1, coalesce($1, $2):fp64?]
+  Project[_ => $1, coalesce($1, $2):fp64?]
     Read[schema.table => name:string?, num:fp64?, other_num:fp64?, id:i64]
 
 Root[name, parent, sum, count]
@@ -35,7 +35,7 @@ Root[name, num, id]
     Read[schema.table => name:string?, num:fp64?, id:i64]
 
 Root[result]
-  Project[$0, $1, $2]
+  Project[_ => $0, $1, $2]
     Filter[eq($2, 100):boolean => $0, $1, $2]
       Read[orders => customer:string, amount:fp64, order_id:i64]
 

examples/advanced_usage.rs

@@ -42,7 +42,7 @@ Functions:
 === Plan
 Root[revenue]
   Filter[gt($2, 100):boolean => $0, $1]
-    Project[$0, $1, multiply($0, $1):fp64?]
+    Project[_ => $0, $1, multiply($0, $1):fp64?]
       Read[orders => quantity:i32?, price:fp64?]
 "#;
 

examples/basic_usage.rs

@@ -18,7 +18,7 @@ Functions:
 === Plan
 Root[revenue]
   Filter[gt($2, 100):boolean => $0, $1]
-    Project[$0, $1, multiply($0, $1):fp64?]
+    Project[_ => $0, $1, multiply($0, $1):fp64?]
       Read[orders => quantity:i32?, price:fp64?]
 "#;
 

src/cli.rs

@@ -484,7 +484,7 @@ mod tests {
 
     const BASIC_PLAN: &str = r#"=== Plan
 Root[result]
-  Project[$0, $1]
+  Project[_ => $0, $1]
     Read[data => a:i64, b:string]
 "#;
 
@@ -497,7 +497,7 @@ Functions:
 === Plan
 Root[result]
   Filter[gt($2, 100):boolean => $0, $1, $2]
-    Project[$0, $1, $2]
+    Project[_ => $0, $1, $2]
       Read[data => a:i64, b:string, c:i32]
 "#;
 
@@ -523,7 +523,7 @@ Root[result]
         let output_content = String::from_utf8(output).unwrap();
         assert!(output_content.contains("=== Plan"));
         assert!(output_content.contains("Root[result]"));
-        assert!(output_content.contains("Project[$0, $1]"));
+        assert!(output_content.contains("Project[_]"));
         assert!(output_content.contains("Read[data => a:i64, b:string]"));
     }
 
@@ -644,7 +644,7 @@ Root[result]
         let output_content = String::from_utf8(output).unwrap();
         assert!(output_content.contains("=== Plan"));
         assert!(output_content.contains("Root[result]"));
-        assert!(output_content.contains("Project[$0, $1]"));
+        assert!(output_content.contains("Project[_]"));
         assert!(output_content.contains("Read[data => a:i64, b:string]"));
     }
 

src/lib.rs

@@ -47,7 +47,7 @@ use textify::plan::PlanWriter;
 /// let plan_text = r#"
 /// === Plan
 /// Root[c, d]
-///   Project[$1, 42]
+///   Project[_ => $1, 42]
 ///     Read[schema.table => a:i64, b:string?]
 /// "#;
 ///
@@ -108,7 +108,7 @@ pub fn parse_with_registry(
 /// let plan: Plan = parse(r#"
 /// === Plan
 /// Root[result]
-///   Project[$0, $1]
+///   Project[_ => $0, $1]
 ///     Read[data => a:i64, b:string]
 /// "#).unwrap();
 ///
@@ -142,7 +142,7 @@ pub fn format(plan: &Plan) -> (String, Vec<FormatError>) {
 /// let plan = parse(r#"
 /// === Plan
 /// Root[result]
-///   Project[$0, 42]
+///   Project[_ => $0, 42]
 ///     Read[data => a:i64]
 /// "#).unwrap();
 ///

src/parser/expression_grammar.pest

@@ -300,9 +300,17 @@ virtual_row           = { "(" ~ sp ~ expression_list? ~ sp ~ ")" }
 
 filter_relation = { "Filter" ~ "[" ~ expression ~ (sp ~ reference_output)? ~ "]" }
 
-project_relation      = { "Project" ~ "[" ~ project_argument_list ~ "]" }
-project_argument_list = { (project_argument ~ (sp ~ "," ~ sp ~ project_argument)*)? }
-project_argument      = { reference | expression }
+// Project has no relation parameters, so `_` marks the empty parameter list.
+// Compact output combines input references and added expressions; explicit
+// output declares only the expressions appended to the inherited input fields.
+project_relation         = { "Project" ~ "[" ~ empty ~ (sp ~ project_output)? ~ "]" }
+project_output           = { implicit_project_output | explicit_project_output }
+implicit_project_output  = { "=>" ~ sp ~ project_argument_list }
+explicit_project_output  = { ("+>" ~ sp ~ project_additions ~ (sp ~ explicit_emit)?) | explicit_emit }
+project_argument_list    = { empty | (project_argument ~ (sp ~ "," ~ sp ~ project_argument)*) }
+project_argument         = { reference | expression }
+project_additions        = { project_expression_list }
+project_expression_list  = { empty | expression_list }
 
 // Aggregate relation: groups by specified fields and applies aggregate functions
 // Format: Aggregate[group_by_fields => output_items]

src/parser/extensions.rs

@@ -737,7 +737,7 @@ Types:
   # 11 @  1: u!point
 === Plan
 Root[result]
-  Project[$0]
+  Project[_ => $0]
     Read[data => p:point#11]";
         let plan = Parser::parse(plan_text).unwrap();
         let (text, errors) = format(&plan);