Add Constant type/value properties (#280)

* add Constant property resolution function

allow reading constant value/expr/is_literal and type (this one serialized to a json string since there is no impl to convert it to FieldValue)

* add Constant property rustdocs example

* add Constant property rustdoc schema

* dep: add serde_json for Constant property Type

* fix clippy

* uglify with rustfmt

* Update src/rustdoc_schema.graphql

Co-authored-by: Predrag Gruevski <2348618+obi1kenobi@users.noreply.github.com>

* squeeze doc comment

* add a doc comment note referencing a more comprehensive example

to avoid repeating said example

* add type_ field to AssociatedConstant property resolution function

(temporary in the json string format)

* add type_ field to AssociatedConstant property rustdoc schema

* split schema docs so that each Constant property is documented

* update schema doc comment

* update schema docs trait name

* fix a typo in schema docs

* remove type Assoc/Const property

until trustfall adds proper support for custom scalar types

* remove type Assoc/Const property from schema

* fix a typo in schema docs

Co-authored-by: Predrag Gruevski <2348618+obi1kenobi@users.noreply.github.com>

* dep: remove serde_json since Constant property Type was removed

Co-authored-by: Predrag Gruevski <2348618+obi1kenobi@users.noreply.github.com>

* remove unstable rustdocs example for Constant properties

Co-authored-by: Predrag Gruevski <2348618+obi1kenobi@users.noreply.github.com>

* Update formatting of the schema docs

Co-authored-by: Predrag Gruevski <2348618+obi1kenobi@users.noreply.github.com>

* Update AssociatedConstant example to refer to a const generic

* Update Constant test with extra properties

expr/value/is_literal

---------

Co-authored-by: Predrag Gruevski <2348618+obi1kenobi@users.noreply.github.com>

src/adapter/mod.rs

@@ -140,6 +140,7 @@ impl<'a> Adapter<'a> for RustdocAdapter<'a> {
                 "AssociatedConstant" => {
                     properties::resolve_associated_constant_property(contexts, property_name)
                 }
+                "Constant" => properties::resolve_constant_property(contexts, property_name),
                 _ => unreachable!("resolve_property {type_name} {property_name}"),
             }
         }

src/adapter/properties.rs

@@ -423,3 +423,39 @@ pub(crate) fn resolve_associated_constant_property<'a>(
         _ => unreachable!("AssociatedConstant property {property_name}"),
     }
 }
+
+pub(crate) fn resolve_constant_property<'a>(
+    contexts: ContextIterator<'a, Vertex<'a>>,
+    property_name: &str,
+) -> ContextOutcomeIterator<'a, Vertex<'a>, FieldValue> {
+    match property_name {
+        "expr" => resolve_property_with(
+            contexts,
+            field_property!(as_item, inner, {
+                let ItemEnum::Constant(c) = &inner else {
+                    unreachable!("expected to have a Constant")
+                };
+                c.expr.clone().into()
+            }),
+        ),
+        "value" => resolve_property_with(
+            contexts,
+            field_property!(as_item, inner, {
+                let ItemEnum::Constant(c) = &inner else {
+                    unreachable!("expected to have a Constant")
+                };
+                c.value.clone().into()
+            }),
+        ),
+        "is_literal" => resolve_property_with(
+            contexts,
+            field_property!(as_item, inner, {
+                let ItemEnum::Constant(c) = &inner else {
+                    unreachable!("expected to have a Constant")
+                };
+                c.is_literal.into()
+            }),
+        ),
+        _ => unreachable!("Constant property {property_name}"),
+    }
+}

src/adapter/tests.rs

@@ -171,6 +171,9 @@ fn rustdoc_finds_consts() {
         item {
             ... on Constant {
                 name @output
+                expr @output
+                value @output
+                is_literal @output
 
                 importable_path {
                     path @output
@@ -190,24 +193,48 @@ fn rustdoc_finds_consts() {
     struct Output {
         name: String,
         path: Vec<String>,
+        expr: String,
+        value: Option<String>,
+        is_literal: bool,
+    }
+    #[derive(Debug, PartialOrd, Ord, PartialEq, Eq, serde::Deserialize)]
+    struct OutputSimple {
+        name: String,
+        path: Vec<String>,
     }
 
     let mut results: Vec<_> =
         trustfall::execute_query(&schema, adapter.clone(), query, variables.clone())
             .expect("failed to run query")
-            .map(|row| row.try_into_struct().expect("shape mismatch"))
+            .map(|row| row.try_into_struct::<Output>().expect("shape mismatch"))
             .collect();
     results.sort_unstable();
+    // to compare to GlobalValue that doesn't Constant-specific properties
+    let mut results_simple: Vec<_> =
+        trustfall::execute_query(&schema, adapter.clone(), query, variables.clone())
+            .expect("failed to run query")
+            .map(|row| {
+                row.try_into_struct::<OutputSimple>()
+                    .expect("shape mismatch")
+            })
+            .collect();
+    results_simple.sort_unstable();
 
     similar_asserts::assert_eq!(
         vec![
             Output {
                 name: "FIRST".into(),
                 path: vec!["consts".into(), "FIRST".into()],
+                expr: "1".to_string(),
+                value: Some("1u32".to_string()),
+                is_literal: true,
             },
             Output {
                 name: "SECOND".into(),
                 path: vec!["consts".into(), "inner".into(), "SECOND".into()],
+                expr: "2".to_string(),
+                value: Some("2i64".to_string()),
+                is_literal: true,
             },
         ],
         results
@@ -232,10 +259,13 @@ fn rustdoc_finds_consts() {
     let mut global_values_results: Vec<_> =
         trustfall::execute_query(&schema, adapter, global_values_query, variables)
             .expect("failed to run query")
-            .map(|row| row.try_into_struct().expect("shape mismatch"))
+            .map(|row| {
+                row.try_into_struct::<OutputSimple>()
+                    .expect("shape mismatch")
+            })
             .collect();
     global_values_results.sort_unstable();
-    assert_eq!(results, global_values_results);
+    assert_eq!(results_simple, global_values_results);
 }
 
 #[test]

src/rustdoc_schema.graphql

@@ -671,6 +671,61 @@ type Constant implements Item & Importable & GlobalValue {
   attrs: [String!]!
   visibility_limit: String!
 
+  # properties for Constant
+  """
+  The expression of the constant, if any, as a Rust literal or `"_"`. For example:
+  ```rust
+  //                                 // expr
+  const MIN     : usize = 16       ; // 16
+  const MIN_SIZE: usize = MIN      ; // "MIN", referring to the other constant's name
+  const LOG_AS  : &str  = "batch"  ; // "\"batch\"", including escaped quotes
+  const YEAR    : Years = Years(42); // "_"
+  const EXPR_2_2: i32   = 2 + 2    ; // "_"
+  const FN_FIVE : i32   = five()   ; // "_"
+  const fn five() -> i32 { 5 };
+  struct Years(i32);
+  ```
+  If the constant is set:
+
+    - to be equal to another constant, `expr` holds the name of that other constant.
+    - by evaluating a `const` expression, such as `2 + 2` or a `const fn` call, `expr` is `"_"` instead of including the full expression.
+  """
+  expr: String
+  """
+  The value of the constant, if any, as a Rust literal. For example:
+  ```rust
+  //                                 // value
+  const MIN     : usize = 16       ; // "16usize"
+  const MIN_SIZE: usize = MIN      ; // "16usize"
+  const LOG_AS  : &str  = "batch"  ; // None
+  const YEAR    : Years = Years(42); // None
+  const EXPR_2_2: i32   = 2 + 2    ; // "4i32"
+  const FN_FIVE : i32   = five()   ; // "5i32"
+  const fn five() -> i32 { 5 };
+  struct Years(i32);
+  ```
+  If the constant is set:
+
+    - to be equal to another constant, `value` holds the value of that other constant.
+    - by evaluating a `const` expression, such as `2 + 2` or a `const fn` call, `value` is evaluated
+  """
+  value: String
+  """
+  The literal flag of the constant. For example:
+  ```rust
+  //                                 // is_literal
+  const MIN     : usize = 16       ; // true
+  const MIN_SIZE: usize = MIN      ; // false
+  const LOG_AS  : &str  = "batch"  ; // true
+  const YEAR    : Years = Years(42); // false
+  const EXPR_2_2: i32   = 2 + 2    ; // false
+  const FN_FIVE : i32   = five()   ; // false
+  const fn five() -> i32 { 5 };
+  struct Years(i32);
+  ```
+  """
+  is_literal: Boolean
+
   # edges from Item
   span: Span
   attribute: [Attribute!]
@@ -858,21 +913,25 @@ type AssociatedConstant implements Item {
 
   For example:
   ```rust
-  trait BatchIterator<const MIN: usize> {
-    const SIZE: usize = 16;  // `"16"` is the default
-    const LOG_AS: &'static str = "batch";  // `"\"batch\""` is the default, including escaped quotes
-    const MIN_SIZE: usize = MIN;  // "MIN" is the default, referring to the other constant's name
+  const fn five() -> i32 { 5 };
+  struct Years(i32);
+  trait MyTrait<const MIN: usize> {           // rustdocs default field
+    const NUM     : i32          = 16       ; // 16
+    const MIN_SIZE: usize        = MIN      ; // "MIN", referring to the other constant's name
+    const LOG_AS  : &'static str = "batch"  ; // "\"batch\"", including escaped quotes
+    const EXPR2_2 : i32          = 2+2      ; // "_"
+    const FN_FIVE : i32          = five()   ; // "_"
+    const YEAR    : Years        = Years(42); // "_"
   }
   ```
 
-  If the associated constant is on a type's inherent impl, the default is always required to be set.
+  If the associated constant is on a type's inherent impl, `default` is always required to be set.
 
-  If the associated constant is set to be equal to another constant, the default holds the name
-  of that other constant.
+  If the associated constant is set:
 
-  If the associated constant is set by evaluating a `const` expression, such as `2 + 2` or
-  a `const fn` call, rustdoc's current behavior is to show a default value of `"_"`
-  instead of evaluating the constant value or including the full expression.
+    - to be equal to another constant, `default` holds the name of that other constant.
+    - by evaluating a `const` expression, such as `2 + 2` or a `const fn` call, 
+      `default` is `"_"` instead of evaluating the constant value or including the full expression.
   """
   default: String