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The Index Library

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Table of Contents

Design Philosophy
Classes -
- Entity
- ASTLocation
- DeclReferenceMap
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Functions -
- ResolveLocationInAST
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AST Files
index-test tool -
- Usage
- Examples
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Design Philosophy

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The Index library is meant to provide the basic infrastructure for - cross-translation-unit analysis and is primarily focused on indexing - related functionality. It provides an API for clients that need to - accurately map the AST nodes of the ASTContext to the locations in the source files. -It also allows them to analyze information across multiple translation units.

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As a "general rule", ASTContexts are considered the primary source of -information that a client wants about a translation unit. There will be no such class as an - "indexing database" that stores, for example, source locations of identifiers separately from ASTContext. -All the information that a client needs from a translation unit will be extracted from the ASTContext.

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Classes

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Entity

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To be able to reason about semantically the same Decls that are contained in multiple ASTContexts, the 'Entity' class was introduced. -An Entity is an ASTContext-independent "token" that can be created from a Decl (and a typename in the future) with -the purpose to "resolve" it into a Decl belonging to another ASTContext. Some examples to make the concept of Entities more clear:

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-t1.c: -

-void foo(void);
-void bar(void);
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-t2.c: -

-void foo(void) {
-}
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-Translation unit t1.c contains 2 Entities foo and bar, while t2.c contains 1 Entity foo. -Entities are uniqued in such a way that the Entity* pointer for t1.c/foo is the same as the Entity* pointer for t2.c/foo. -An Entity doesn't convey any information about the declaration, it is more like an opaque pointer used only to get the -associated Decl out of an ASTContext so that the actual information for the declaration can be accessed. -Another important aspect of Entities is that they can only be created/associated for declarations that are visible outside the -translation unit. This means that for: -

-t3.c: -

-static void foo(void);
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-there can be no Entity (if you ask for the Entity* of the static function foo you'll get a null pointer). -This is for 2 reasons: -

To preserve the invariant that the same Entity* pointers refer to the same semantic Decls. - In the above example t1.c/foo and t2.c/foo are the same, while t3.c/foo is different.
The purpose of Entity is to get the same semantic Decl from multiple ASTContexts. For a Decl that is not visible - outside of its own translation unit, you don't need an Entity since it won't appear in another ASTContext.

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ASTLocation

- -Encapsulates a "point" in the AST tree of the ASTContext. -It represents either a Decl*, or a Stmt* along with its immediate Decl* parent. -An example for its usage is that libIndex will provide the references of foo in the form of ASTLocations, -"pointing" at the expressions that reference foo. - -

DeclReferenceMap

- -Accepts an ASTContext and creates a mapping from NamedDecls to the ASTLocations that reference them (in the same ASTContext). - -

Functions

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ResolveLocationInAST

- -A function that accepts an ASTContext and a SourceLocation which it resolves into an ASTLocation. - -

AST Files

- -The precompiled headers implementation of clang (PCH) is ideal for storing an ASTContext in a compact form that -will be loaded later for AST analysis. An "AST file" refers to a translation unit that was "compiled" into a precompiled header file. - -

index-test tool

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Usage

- -A command-line tool that exercises the libIndex API, useful for testing its features. -As input it accepts multiple AST files (representing multiple translation units) and a few options: - -

-   -point-at  [file:line:column]
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-Resolves a [file:line:column] triplet into a ASTLocation from the first AST file. If no other option is specified, it prints the ASTLocation. -It also prints a declaration's associated doxygen comment, if one is available. -

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-   -print-refs
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-Prints the ASTLocations that reference the declaration that was resolved out of the [file:line:column] triplet -

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-   -print-defs
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-Prints the ASTLocations that define the resolved declaration -

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-   -print-decls
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-Prints the ASTLocations that declare the resolved declaration -

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Examples

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-Here's an example of using index-test: -

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-We have 3 files, -

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-foo.h: -

-extern int global_var;
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-void foo_func(int param1);
-void bar_func(void);
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- -t1.c: -

-#include "foo.h"
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-void foo_func(int param1) {
-  int local_var = global_var;
-  for (int for_var = 100; for_var < 500; ++for_var) {
-    local_var = param1 + for_var;
-  }
-  bar_func();
-}
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- -t2.c: -

-#include "foo.h"
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-int global_var = 10;
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-void bar_func(void) {
-  global_var += 100;
-  foo_func(global_var);
-}
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-You first get AST files out of t1.c and t2.c: - -

-$ clang -emit-ast t1.c -o t1.ast
-$ clang -emit-ast t2.c -o t2.ast
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-Find the ASTLocation under this position of t1.c: -

-[...]
-void foo_func(int param1) {
-  int local_var = global_var;
-                      ^
-[...]
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-$ index-test t1.ast -point-at t1.c:4:23
-> [Decl: Var local_var | Stmt: DeclRefExpr global_var] <t1.c:4:19, t1.c:4:19>
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-Find the declaration: - -

-$ index-test t1.ast -point-at t1.c:4:23 -print-decls
-> [Decl: Var global_var] <foo.h:1:12, foo.h:1:12>
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-Find the references: - -

-$ index-test t1.ast t2.ast -point-at t1.c:4:23 -print-refs
-> [Decl: Var local_var | Stmt: DeclRefExpr global_var] <t1.c:4:19, t1.c:4:19>
-> [Decl: Function bar_func | Stmt: DeclRefExpr global_var] <t2.c:6:3, t2.c:6:3>
-> [Decl: Function bar_func | Stmt: DeclRefExpr global_var] <t2.c:7:12, t2.c:7:12>
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-Find definitions: - -

-$ index-test t1.ast t2.ast -point-at t1.c:4:23 -print-defs
-> [Decl: Var global_var] <t2.c:3:5, t2.c:3:18>
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