First attempt at making the typing diagnositcs prettier

src/checker.ts

@@ -35,8 +35,24 @@ abstract class TypeBase {
 
   public abstract readonly kind: TypeKind;
 
+  public next: Type = this as any;
+
+  public constructor(
+    public node: Syntax | null = null
+  ) {
+
+  }
+
+  public static join(a: Type, b: Type): void {
+    const keep = a.next;
+    a.next = b;
+    b.next = keep;
+  }
+
   public abstract getTypeVars(): Iterable<TVar>;
 
+  public abstract shallowClone(): Type;
+
   public abstract substitute(sub: TVSub): Type;
 
   public hasTypeVar(tv: TVar): boolean {
@@ -56,6 +72,7 @@ class TVar extends TypeBase {
 
   public constructor(
     public id: number,
+    public node: Syntax | null = null,
   ) {
     super();
   }
@@ -64,6 +81,10 @@ class TVar extends TypeBase {
     yield this;
   }
 
+  public shallowClone(): TVar {
+    return new TVar(this.id, this.node);
+  }
+
   public substitute(sub: TVSub): Type {
     const other = sub.get(this);
     return other === undefined
@@ -79,6 +100,7 @@ export class TArrow extends TypeBase {
   public constructor(
     public paramTypes: Type[],
     public returnType: Type,
+    public node: Syntax | null = null,
   ) {
     super();
   }
@@ -90,6 +112,14 @@ export class TArrow extends TypeBase {
     yield* this.returnType.getTypeVars();
   }
 
+  public shallowClone(): TArrow {
+    return new TArrow(
+      this.paramTypes,
+      this.returnType,
+      this.node,
+    )
+  }
+
   public substitute(sub: TVSub): Type {
     let changed = false;
     const newParamTypes = [];
@@ -104,12 +134,12 @@ export class TArrow extends TypeBase {
     if (newReturnType !== this.returnType) {
       changed = true;
     }
-    return changed ? new TArrow(newParamTypes, newReturnType) : this;
+    return changed ? new TArrow(newParamTypes, newReturnType, this.node) : this;
   }
 
 }
 
-class TCon extends TypeBase {
+export class TCon extends TypeBase {
 
   public readonly kind = TypeKind.Con;
 
@@ -117,8 +147,9 @@ class TCon extends TypeBase {
     public id: number,
     public argTypes: Type[],
     public displayName: string,
+    public node: Syntax | null = null,
   ) {
-    super();
+    super(node);
   }
 
   public *getTypeVars(): Iterable<TVar> {
@@ -127,6 +158,15 @@ class TCon extends TypeBase {
     }
   }
 
+  public shallowClone(): TCon {
+    return new TCon(
+      this.id,
+      this.argTypes,
+      this.displayName,
+      this.node,
+    );
+  }
+
   public substitute(sub: TVSub): Type {
     let changed = false;
     const newArgTypes = [];
@@ -137,21 +177,7 @@ class TCon extends TypeBase {
       }
       newArgTypes.push(newArgType);
     }
-    return changed ? new TCon(this.id, newArgTypes, this.displayName) : this;
+    return changed ? new TCon(this.id, newArgTypes, this.displayName, this.node) : this;
-  }
-
-}
-
-class TAny extends TypeBase {
-
-  public readonly kind = TypeKind.Any;
-
-  public *getTypeVars(): Iterable<TVar> {
-    
-  }
-
-  public substitute(sub: TVSub): Type {
-    return this;
   }
 
 }
@@ -162,8 +188,9 @@ class TTuple extends TypeBase {
 
   public constructor(
     public elementTypes: Type[],
+    public node: Syntax | null = null,
   ) {
-    super();
+    super(node);
   }
 
   public *getTypeVars(): Iterable<TVar> {
@@ -172,6 +199,13 @@ class TTuple extends TypeBase {
     }
   }
 
+  public shallowClone(): TTuple {
+    return new TTuple(
+      this.elementTypes,
+      this.node,
+    );
+  }
+
   public substitute(sub: TVSub): Type {
     let changed = false;
     const newElementTypes = [];
@@ -182,12 +216,12 @@ class TTuple extends TypeBase {
       }
       newElementTypes.push(newElementType);
     }
-    return changed ? new TTuple(newElementTypes) : this;
+    return changed ? new TTuple(newElementTypes, this.node) : this;
   }
 
 }
 
-class TLabeled extends TypeBase {
+export class TLabeled extends TypeBase {
 
   public readonly kind = TypeKind.Labeled;
 
@@ -197,8 +231,9 @@ class TLabeled extends TypeBase {
   public constructor(
     public name: string,
     public type: Type,
+    public node: Syntax | null = null,
   ) {
-    super();
+    super(node);
   }
 
   public find(): TLabeled {
@@ -214,14 +249,22 @@ class TLabeled extends TypeBase {
     return this.type.getTypeVars();
   }
 
+  public shallowClone(): TLabeled {
+    return new TLabeled(
+      this.name,
+      this.type,
+      this.node,
+    );
+  }
+
   public substitute(sub: TVSub): Type {
     const newType = this.type.substitute(sub);
-    return newType !== this.type ? new TLabeled(this.name, newType) : this;
+    return newType !== this.type ? new TLabeled(this.name, newType, this.node) : this;
   }
 
 }
 
-class TRecord extends TypeBase {
+export class TRecord extends TypeBase {
 
   public readonly kind = TypeKind.Record;
 
@@ -230,8 +273,9 @@ class TRecord extends TypeBase {
   public constructor(
     public decl: StructDeclaration,
     public fields: Map<string, Type>,
+    public node: Syntax | null = null,
   ) {
-    super();
+    super(node);
   }
 
   public *getTypeVars(): Iterable<TVar> {
@@ -240,6 +284,14 @@ class TRecord extends TypeBase {
     }
   }
 
+  public shallowClone(): TRecord {
+    return new TRecord(
+      this.decl,
+      this.fields,
+      this.node
+    );
+  }
+
   public substitute(sub: TVSub): Type {
     let changed = false;
     const newFields = new Map();
@@ -250,7 +302,7 @@ class TRecord extends TypeBase {
       }
       newFields.set(key, newType);
     }
-    return changed ? new TRecord(this.decl, newFields) : this;
+    return changed ? new TRecord(this.decl, newFields, this.node) : this;
   }
 
 }
@@ -684,7 +736,9 @@ export class Checker {
           this.diagnostics.add(new BindingNotFoudDiagnostic(node.name.name.text, node.name.name));
           return new TAny();
         }
-        return this.instantiate(scheme, node);
+        const type = this.instantiate(scheme, node);
+        type.node = node;
+        return type;
       }
 
       case SyntaxKind.MemberExpression:
@@ -733,6 +787,8 @@ export class Checker {
             ty = this.getIntType();
             break;
         }
+        ty = ty.shallowClone();
+        ty.node = node;
         return ty;
       }
 
@@ -741,7 +797,7 @@ export class Checker {
         const scheme = this.lookup(node.name.text);
         if (scheme === null) {
           this.diagnostics.add(new BindingNotFoudDiagnostic(node.name.text, node.name));
-          return new TAny();
+          return this.createTypeVar();
         }
         const type = this.instantiate(scheme, node.name);
         assert(type.kind === TypeKind.Con);
@@ -749,7 +805,7 @@ export class Checker {
         for (const element of node.elements) {
           argTypes.push(this.inferExpression(element));
         }
-        return new TCon(type.id, argTypes, type.displayName);
+        return new TCon(type.id, argTypes, type.displayName, node);
       }
 
       case SyntaxKind.StructExpression:
@@ -786,7 +842,7 @@ export class Checker {
               throw new Error(`Unexpected ${member}`);
           }
         }
-        const type = new TRecord(recordType.decl, fields);
+        const type = new TRecord(recordType.decl, fields, node);
         this.addConstraint(
           new CEqual(
             recordType,
@@ -836,7 +892,9 @@ export class Checker {
           this.diagnostics.add(new BindingNotFoudDiagnostic(node.name.text, node.name));
           return new TAny();
         }
-        return this.instantiate(scheme, node.name);
+        const type = this.instantiate(scheme, node.name);
+        type.node = node;
+        return type;
       }
 
       default:
@@ -1338,7 +1396,7 @@ export class Checker {
 
     while (queue.length > 0) {
 
-      const constraint = queue.pop()!;
+      const constraint = queue.shift()!;
 
       switch (constraint.kind) {
 
@@ -1382,6 +1440,7 @@ export class Checker {
         return false;
       }
       solution.set(left, right);
+      TypeBase.join(left, right);
       return true;
     }
 
@@ -1390,6 +1449,7 @@ export class Checker {
     }
 
     if (left.kind === TypeKind.Any || right.kind === TypeKind.Any) {
+      TypeBase.join(left, right);
       return true;
     }
 
@@ -1408,6 +1468,9 @@ export class Checker {
       if (!this.unify(left.returnType, right.returnType, solution, constraint)) {
         success = false;
       }
+      if (success) {
+        TypeBase.join(left, right);
+      }
       return success;
     }
 
@@ -1429,6 +1492,9 @@ export class Checker {
             success = false;
           }
         }
+        if (success) {
+          TypeBase.join(left, right);
+        }
         return success;
       }
     }
@@ -1456,6 +1522,9 @@ export class Checker {
         }
       }
       delete right.fields;
+      if (success) {
+        TypeBase.join(left, right);
+      }
       return success;
     }
 
@@ -1480,6 +1549,9 @@ export class Checker {
       for (const fieldName of remaining) {
         this.diagnostics.add(new FieldDoesNotExistDiagnostic(left, fieldName));
       }
+      if (success) {
+        TypeBase.join(left, right);
+      }
       return success;
     }
 
@@ -1497,6 +1569,9 @@ export class Checker {
           this.diagnostics.add(new FieldMissingDiagnostic(left, fieldName));
         }
       }
+      if (success) {
+        TypeBase.join(left, right);
+      }
       return success;
     }
 

src/diagnostics.ts

@@ -1,6 +1,6 @@
 
 import { describe } from "yargs";
-import { TypeKind, type Type, type TArrow } from "./checker";
+import { TypeKind, type Type, type TArrow, TRecord } from "./checker";
 import { Syntax, SyntaxKind, TextFile, TextPosition, TextRange, Token } from "./cst";
 import { countDigits } from "./util";
 
@@ -215,6 +215,14 @@ export function describeType(type: Type): string {
   }
 }
 
+function getFirstNodeInTypeChain(type: Type): Syntax | null {
+  let curr = type.next;
+  while (curr !== type && (curr.kind === TypeKind.Var || curr.node === null)) {
+    curr = curr.next;
+  }
+  return curr.node;
+}
+
 export class UnificationFailedDiagnostic {
 
   public readonly level = Level.Error;
@@ -228,6 +236,8 @@ export class UnificationFailedDiagnostic {
   }
 
   public format(): string {
+    const leftNode = getFirstNodeInTypeChain(this.left);
+    const rightNode = getFirstNodeInTypeChain(this.right);
     const node = this.nodes[0];
     let out = ANSI_FG_RED + ANSI_BOLD + `error: ` + ANSI_RESET
         + `unification of ` + ANSI_FG_GREEN + describeType(this.left) + ANSI_RESET
@@ -238,6 +248,16 @@ export class UnificationFailedDiagnostic {
       out += '  ... in an instantiation of the following expression\n\n'
       out += printNode(node, { indentation: i === 0 ? '  ' : '    ' }) + '\n';
     }
+    if (leftNode !== null) {
+      out += ANSI_FG_YELLOW + ANSI_BOLD + `info: ` + ANSI_RESET
+          + `type ` + ANSI_FG_GREEN + describeType(this.left) + ANSI_RESET + ` was inferred from this expression:\n\n`
+          + printNode(leftNode) + '\n';
+    }
+    if (rightNode !== null) {
+      out += ANSI_FG_YELLOW + ANSI_BOLD + `info: ` + ANSI_RESET
+          + `type ` + ANSI_FG_GREEN + describeType(this.right) + ANSI_RESET + ` was inferred from this expression:\n\n`
+          + printNode(rightNode) + '\n';
+    }
     return out;
   }
 
@@ -277,9 +297,13 @@ export class FieldMissingDiagnostic {
   }
 
   public format(): string {
-    return ANSI_FG_RED + ANSI_BOLD + 'error: ' + ANSI_RESET 
+    let out = ANSI_FG_RED + ANSI_BOLD + 'error: ' + ANSI_RESET 
          + `field '${this.fieldName}' is missing from `
          + describeType(this.recordType) + '\n\n';
+    if (this.recordType.node !== null) {
+      out += printNode(this.recordType.node) + '\n';
+    }
+    return out
   }
 
 }
@@ -289,8 +313,6 @@ export class FieldDoesNotExistDiagnostic {
   public readonly level = Level.Error;
 
   public constructor(
-    public recordType: TRecord,
-    public fieldName: string,
   ) {
 
   }

src/test/type-inference.md

@@ -69,3 +69,4 @@ let is_odd x.
 
 not (is_even True)
 ```
+