Remove DeclaredEntity.getDecl().

It's not particularly useful except for functions, and the name is easy to confuse with `Entity.getDeclaration()`. Instead we now have `getFuncDecl()` just for functions, and a bit more API on `Function` to avoid its use where possible.

ql/src/semmle/go/Decls.qll

@@ -156,7 +156,7 @@ class FuncDecl extends @funcdecl, Decl, Documentable, FuncDef {
   override BlockStmt getBody() { result = getChildStmt(2) }
 
   /** Gets the function declared by this function declaration. */
-  DeclaredFunction getFunction() { this = result.getDecl() }
+  DeclaredFunction getFunction() { this = result.getFuncDecl() }
 
   override string toString() { result = "function declaration" }
 }

ql/src/semmle/go/Expr.qll

@@ -482,7 +482,7 @@ class CallExpr extends CallOrConversionExpr {
    * interface type.
    */
   FuncDef getACallee() {
-    result = getTarget().(DeclaredFunction).getDecl()
+    result = getTarget().(DeclaredFunction).getFuncDecl()
     or
     exists(SelectorExpr sel, InterfaceType declaredRecv, Type actualRecv |
       sel = getCalleeExpr().stripParens() and

ql/src/semmle/go/Scopes.qll

@@ -128,9 +128,6 @@ class Entity extends @object {
 
 /** A declared entity (that is, type, constant, variable or function). */
 class DeclaredEntity extends Entity, @declobject {
-  /** Gets the declaration of this entity. */
-  Decl getDecl() { none() }
-
   /** Gets the expression to which this entity is initialized, if any. */
   Expr getInit() {
     exists(ValueSpec spec, int i |
@@ -151,9 +148,6 @@ class TypeEntity extends Entity, @typeobject { }
 
 /** A declared named type. */
 class DeclaredType extends TypeEntity, DeclaredEntity, @decltypeobject {
-  /** Gets the declaration of this type. */
-  override TypeDecl getDecl() { result.getASpec() = this.getSpec() }
-
   /** Gets the declaration specifier declaring this type. */
   TypeSpec getSpec() { result.getNameExpr() = this.getDeclaration() }
 }
@@ -175,9 +169,6 @@ class Constant extends ValueEntity, @constobject { }
 
 /** A declared constant. */
 class DeclaredConstant extends Constant, DeclaredEntity, @declconstobject {
-  /** Gets the declaration of this constant. */
-  override ConstDecl getDecl() { result.getASpec() = this.getSpec() }
-
   /** Gets the declaration specifier declaring this constant. */
   ValueSpec getSpec() { result.getANameExpr() = this.getDeclaration() }
 }
@@ -195,9 +186,6 @@ class Variable extends ValueEntity, @varobject { }
 
 /** A declared variable. */
 class DeclaredVariable extends Variable, DeclaredEntity, @declvarobject {
-  /** Gets the declaration of this variable. */
-  override VarDecl getDecl() { result.getASpec() = this.getSpec() }
-
   /** Gets the declaration specifier declaring this variable. */
   ValueSpec getSpec() { result.getANameExpr() = this.getDeclaration() }
 }
@@ -297,6 +285,12 @@ class Function extends ValueEntity, @functionobject {
 
   /** Gets the body of this function, if any. */
   BlockStmt getBody() { none() }
+
+  /** Gets the `i`th parameter of this function. */
+  Parameter getParameter(int i) { none() }
+
+  /** Gets a parameter of this function. */
+  Parameter getAParameter() { result = getParameter(_) }
 }
 
 /** A method, that is, a function with a receiver variable. */
@@ -371,9 +365,11 @@ class Method extends Function {
 /** A declared function. */
 class DeclaredFunction extends Function, DeclaredEntity, @declfunctionobject {
   /** Gets the declaration of this function. */
-  override FuncDecl getDecl() { result.getNameExpr() = this.getDeclaration() }
+  FuncDecl getFuncDecl() { result.getNameExpr() = this.getDeclaration() }
 
-  override BlockStmt getBody() { result = getDecl().getBody() }
+  override BlockStmt getBody() { result = getFuncDecl().getBody() }
+
+  override Parameter getParameter(int i) { result = getFuncDecl().getParameter(i) }
 
   override predicate mayHaveSideEffects() {
     not exists(getBody())

ql/src/semmle/go/dataflow/internal/DataFlowUtil.qll

@@ -223,7 +223,7 @@ class GlobalFunctionNode extends FunctionNode, MkGlobalFunctionNode {
   GlobalFunctionNode() { this = MkGlobalFunctionNode(func) }
 
   override ParameterNode getParameter(int i) {
-    result = parameterNode(func.(DeclaredFunction).getDecl().getParameter(i))
+    result = parameterNode(func.getParameter(i))
   }
 
   override string getName() { result = func.getName() }