Clean up @field and @fieldparent usage

* Centralise use of raw types and database predicates in FieldParent and FieldBase classes
* Deduplicate type predicates common to all fields
* Deduplicate predicates common to function parameters and results

Author: smowton

ql/src/semmle/go/AST.qll

@@ -20,7 +20,7 @@ class AstNode extends @node, Locatable {
     result = this.(StmtParent).getChildStmt(i) or
     result = this.(DeclParent).getDecl(i) or
     result = this.(GenDecl).getSpec(i) or
-    fields(result, this, i)
+    result = this.(FieldParent).getField(i)
   }
 
   /**
@@ -140,6 +140,29 @@ class DeclParent extends @declparent, AstNode {
   int getNumDecl() { result = count(getADecl()) }
 }
 
+/**
+ * An AST node whose children include fields.
+ */
+class FieldParent extends @fieldparent, AstNode {
+  /**
+   * Gets the `i`th field of this node.
+   *
+   * Note that the precise indices of fields are considered an implementation detail
+   * and are subject to change without notice.
+   */
+  FieldBase getField(int i) { fields(result, this, i) }
+
+  /**
+   * Gets a child field of this node in the AST.
+   */
+  FieldBase getAField() { result = getField(_) }
+
+  /**
+   * Gets the number of child fields of this node.
+   */
+  int getNumFields() { result = count(getAField()) }
+}
+
 /**
  * An AST node which may induce a scope.
  *

ql/src/semmle/go/Decls.qll

@@ -7,7 +7,7 @@ import go
 /**
  * A declaration.
  */
-class Decl extends @decl, ExprParent, StmtParent {
+class Decl extends @decl, ExprParent, StmtParent, FieldParent {
   /**
    * Gets the kind of this declaration, which is an integer value representing the declaration's
    * node type.
@@ -363,11 +363,10 @@ class TypeSpec extends @typespec, Spec {
 }
 
 /**
- * A field declaration in a struct type.
+ * A field declaration, of a struct, a function (in which case this is a parameter or result variable),
+ * or an interface (in which case this is a method or embedding spec).
  */
-class FieldDecl extends @field, Documentable, ExprParent {
-  FieldDecl() { fields(this, any(StructTypeExpr st), _) }
-
+class FieldBase extends @field, ExprParent {
   /**
    * Gets the expression representing the type of the fields declared in this declaration.
    */
@@ -377,6 +376,15 @@ class FieldDecl extends @field, Documentable, ExprParent {
    * Gets the type of the fields declared in this declaration.
    */
   Type getType() { result = getTypeExpr().getType() }
+}
+
+/**
+ * A field declaration in a struct type.
+ */
+class FieldDecl extends FieldBase, Documentable, ExprParent {
+  StructTypeExpr st;
+
+  FieldDecl() { this = st.getField(_) }
 
   /**
    * Gets the expression representing the name of the `i`th field declared in this declaration
@@ -391,7 +399,7 @@ class FieldDecl extends @field, Documentable, ExprParent {
   Expr getTag() { result = getChildExpr(-1) }
 
   /** Gets the struct type expression to which this field declaration belongs. */
-  StructTypeExpr getDeclaringStructTypeExpr() { fields(this, result, _) }
+  StructTypeExpr getDeclaringStructTypeExpr() { result = st }
 
   /** Gets the struct type to which this field declaration belongs. */
   StructType getDeclaringType() { result = getDeclaringStructTypeExpr().getType() }
@@ -407,74 +415,66 @@ class EmbeddedFieldDecl extends FieldDecl {
 }
 
 /**
- * A parameter declaration.
+ * A function parameter or result variable declaration.
  */
-class ParameterDecl extends @field, Documentable, ExprParent {
-  ParameterDecl() {
-    exists(int i |
-      fields(this, any(FuncTypeExpr ft), i) and
-      i >= 0
-    )
-  }
+class ParameterOrResultDecl extends FieldBase, Documentable, ExprParent {
+  int rawIndex;
+  FuncTypeExpr ft;
+
+  ParameterOrResultDecl() { this = ft.getField(rawIndex) }
 
   /**
-   * Gets the function type expression to which this parameter declaration belongs.
+   * Gets the function type expression to which this declaration belongs.
    */
-  FuncTypeExpr getFunctionTypeExpr() { fields(this, result, _) }
+  FuncTypeExpr getFunctionTypeExpr() { result = ft }
 
   /**
-   * Gets the function to which this parameter declaration belongs.
+   * Gets the function to which this declaration belongs.
    */
   FuncDef getFunction() { result.getTypeExpr() = getFunctionTypeExpr() }
 
   /**
-   * Gets the index of this parameter declarations among all parameter declarations of
-   * its associated function type.
+   * Gets the expression representing the name of the `i`th variable declared in this declaration
+   * (0-based).
    */
-  int getIndex() { fields(this, _, result) }
+  Expr getNameExpr(int i) {
+    i >= 0 and
+    result = getChildExpr(i + 1)
+  }
 
   /**
-   * Gets the expression representing the type of the parameters declared in this declaration.
+   * Gets an expression representing the name of a variable declared in this declaration.
    */
-  Expr getTypeExpr() { result = getChildExpr(0) }
+  Expr getANameExpr() { result = getNameExpr(_) }
+}
 
-  /**
-   * Gets the type of the parameters declared in this declaration.
-   */
-  Type getType() { result = getTypeExpr().getType() }
+/**
+ * A parameter declaration.
+ */
+class ParameterDecl extends ParameterOrResultDecl {
+  ParameterDecl() { rawIndex >= 0 }
 
   /**
-   * Gets the expression representing the name of the `i`th parameter declared in this declaration
-   * (0-based).
+   * Gets the index of this parameter declarations among all parameter declarations of
+   * its associated function type.
    */
-  Expr getNameExpr(int i) {
-    i >= 0 and
-    result = getChildExpr(i + 1)
-  }
+  int getIndex() { result = rawIndex }
 
   override string toString() { result = "parameter declaration" }
 }
 
 /**
  * A receiver declaration in a function declaration.
  */
-class ReceiverDecl extends @field, Documentable, ExprParent {
-  ReceiverDecl() { fields(this, any(FuncDecl fd), -1) }
+class ReceiverDecl extends FieldBase, Documentable, ExprParent {
+  FuncDecl fd;
 
-  /**
-   * Gets the function declaration to which this receiver belongs.
-   */
-  FuncDecl getFunction() { fields(this, result, _) }
+  ReceiverDecl() { fd.getField(-1) = this }
 
   /**
-   * Gets the expression representing the type of the receiver declared in this declaration.
-   */
-  Expr getTypeExpr() { result = getChildExpr(0) }
-
-  /**
-   * Gets the type of the receiver declared in this declaration.
+   * Gets the function declaration to which this receiver belongs.
    */
-  Type getType() { result = getTypeExpr().getType() }
+  FuncDecl getFunction() { result = fd }
 
   /**
    * Gets the expression representing the name of the receiver declared in this declaration.
@@ -487,60 +487,26 @@ class ReceiverDecl extends @field, Documentable, ExprParent {
 /**
  * A result variable declaration.
  */
-class ResultVariableDecl extends @field, Documentable, ExprParent {
-  ResultVariableDecl() {
-    exists(int i |
-      fields(this, any(FuncTypeExpr ft), i) and
-      i < 0
-    )
-  }
-
-  /**
-   * Gets the expression representing the type of the result variables declared in this declaration.
-   */
-  Expr getTypeExpr() { result = getChildExpr(0) }
-
-  /**
-   * Gets the type of the result variables declared in this declaration.
-   */
-  Type getType() { result = getTypeExpr().getType() }
-
-  /**
-   * Gets the expression representing the name of the `i`th result variable declared in this declaration
-   * (0-based).
-   */
-  Expr getNameExpr(int i) {
-    i >= 0 and
-    result = getChildExpr(i + 1)
-  }
-
-  /**
-   * Gets an expression representing the name of a result variable declared in this declaration.
-   */
-  Expr getANameExpr() { result = getNameExpr(_) }
-
-  /**
-   * Gets the function type expression to which this result variable declaration belongs.
-   */
-  FuncTypeExpr getFunctionTypeExpr() { fields(this, result, _) }
+class ResultVariableDecl extends ParameterOrResultDecl {
+  ResultVariableDecl() { rawIndex < 0 }
 
   /**
    * Gets the index of this result variable declaration among all result variable declarations of
    * its associated function type.
    */
-  int getIndex() { fields(this, _, -(result + 1)) }
+  int getIndex() { result = -(rawIndex + 1) }
 
   override string toString() { result = "result variable declaration" }
 }
 
 /**
  * A method or embedding specification in an interface type expression.
  */
-class InterfaceMemberSpec extends @field, Documentable, ExprParent {
+class InterfaceMemberSpec extends FieldBase, Documentable, ExprParent {
   InterfaceTypeExpr ite;
   int idx;
 
-  InterfaceMemberSpec() { fields(this, ite, idx) }
+  InterfaceMemberSpec() { this = ite.getField(idx) }
 
   /**
    * Gets the interface type expression to which this member specification belongs.
@@ -552,17 +518,6 @@ class InterfaceMemberSpec extends @field, Documentable, ExprParent {
    * its associated interface type expression.
    */
   int getIndex() { result = idx }
-
-  /**
-   * Gets the expression representing the type of the method or embedding declared in
-   * this specification.
-   */
-  Expr getTypeExpr() { result = getChildExpr(0) }
-
-  /**
-   * Gets the type of the method or embedding declared in this specification.
-   */
-  Type getType() { result = getTypeExpr().getType() }
 }
 
 /**

ql/src/semmle/go/Expr.qll

@@ -792,16 +792,7 @@ class ArrayTypeExpr extends @arraytypeexpr, TypeExpr {
  * struct {x, y int; z float32}
  * ```
  */
-class StructTypeExpr extends @structtypeexpr, TypeExpr {
-  /** Gets the `i`th field declared in this struct type expression (0-based). */
-  FieldDecl getField(int i) { fields(result, this, i) }
-
-  /** Gets a field declared in this struct type expression. */
-  FieldDecl getAField() { result = getField(_) }
-
-  /** Gets the number of fields declared in this struct type expression. */
-  int getNumField() { result = count(getAField()) }
-
+class StructTypeExpr extends @structtypeexpr, TypeExpr, FieldParent {
   override string toString() { result = "struct type" }
 }
 
@@ -814,12 +805,9 @@ class StructTypeExpr extends @structtypeexpr, TypeExpr {
  * func(a, b int, c float32) (float32, bool)
  * ```
  */
-class FuncTypeExpr extends @functypeexpr, TypeExpr, ScopeNode {
+class FuncTypeExpr extends @functypeexpr, TypeExpr, ScopeNode, FieldParent {
   /** Gets the `i`th parameter of this function type (0-based). */
-  ParameterDecl getParameterDecl(int i) {
-    result.getFunctionTypeExpr() = this and
-    result.getIndex() = i
-  }
+  ParameterDecl getParameterDecl(int i) { result = getField(i) and i >= 0 }
 
   /** Gets a parameter of this function type. */
   ParameterDecl getAParameterDecl() { result = getParameterDecl(_) }
@@ -828,10 +816,7 @@ class FuncTypeExpr extends @functypeexpr, TypeExpr, ScopeNode {
   int getNumParameter() { result = count(getAParameterDecl()) }
 
   /** Gets the `i`th result of this function type (0-based). */
-  ResultVariableDecl getResultDecl(int i) {
-    result.getFunctionTypeExpr() = this and
-    result.getIndex() = i
-  }
+  ResultVariableDecl getResultDecl(int i) { result = getField(-(i + 1)) }
 
   /** Gets a result of this function type. */
   ResultVariableDecl getAResultDecl() { result = getResultDecl(_) }
@@ -854,12 +839,9 @@ class FuncTypeExpr extends @functypeexpr, TypeExpr, ScopeNode {
  * interface { Read(p []byte) (n int, err error); Close() error}
  * ```
  */
-class InterfaceTypeExpr extends @interfacetypeexpr, TypeExpr {
+class InterfaceTypeExpr extends @interfacetypeexpr, TypeExpr, FieldParent {
   /** Gets the `i`th method specification of this interface type. */
-  MethodSpec getMethod(int i) {
-    result.getInterfaceTypeExpr() = this and
-    result.getIndex() = i
-  }
+  MethodSpec getMethod(int i) { result = getField(i) }
 
   /** Gets a method of this interface type. */
   MethodSpec getAMethod() { result = getMethod(_) }