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Build Transform depsScan

Author:Rawld Gill

Summary

Scans AMD and legacy module for dependencies; automatically convert legacy modules to AMD modules (both normal code modules and NLS modules); interns strings for legacy modules.

Description

Modules tagged with “amd” or containing the dojo pragma “//>> pure-amd” are evaluated in the global scope with global define() and global require() replaced with thunk functions execute a no-op. This allows the transform to gain access to the dependency vector and absolute module identifier, if any, without using regular expressions. Well-constructed AMD modules should not depend on or manipulate the environment unless and until their factory functions are applied. Therefore, it is safe to execute these kinds of modules in the build environment.

Note: though bad practice, it is certainly possible to write an AMD module that depends on a certain execution environment when it is evaluated and/or mutates the execution environment is such a way as to cause the build system to crash.

Modules tagged with “nls” must be either AMD NLS modules or legacy NLS modules. AMD NLS modules are evaluated just as if the module was tagged with “amd” as described above. Notice that this allows AMD NLS modules to have dependencies. If a legacy NLS module is detected, then it is automatically converted to the AMD NLS format. Legacy NLS modules are assumed to have no dependencies.

Modules that are not tagged with “amd” and are not NLS modules are scanned for dependencies using a process that depends on regular expressions. Due to the lexical conventions of Javascript, it is impossible to construct a regular expression that can properly differentiate between comments, strings, and regular expression literals (a parser is required that can compute context). Nevertheless, the regular-expression-based dependency scanning process works in all but the most defective cases and is identical to the process that is used with the legacy xdomain loader and build system in v1.6-.

The process begins by interning strings if the profile property internStrings is truthy. Three patterns of expressions are interned:

  • a templatePath property in an object literal (often used to define a dojo.declare’d widget):

    templatePath : dojo.moduleUrl( module , url )

  • assigning to templatePath

    anything templatePath = dojo.moduleUrl( module , `` *url* ``)

  • any dojo.cache expression with either of these formats

    dojo.cache( module , `` *url* ``)

    dojo.cache( module , `` *url* ``, value )

In all cases, the pattern matching algorithm is not sensitive to white space.

Zero or more string resources may be excluded from being interned by placing the resource module identifier in the profile property internStringsSkipList, an array of module identifiers (strings). Module identifiers of non-Javascript resources (e.g. HTML template files) must include the proper file type. For example, the resource at dijit/templates/tree.html has the resource identifier “dijit/templates/TreeNode.html”.

After strings are interned (if necessary), the module is scanned for legacy loader API functions applications (dojo.require, dojo.provide, et al). If no such applications are found, then the module is scanned for AMD define and/or require applications. If found, then the module is assumed to be an AMD module, the transform is advised of any dependencies, and a warning is given stating that the module appears to be a proper AMD module but was not tagged as such. In this case, the resourceTags property of either the profile or the package configuration should be adjusted to properly tag the module. Alternatively, the //>> pure-amd pragma may be added to the module, but this should be considered a short-term solution.

If legacy loader API function applications are discovered, then the module is converted to an AMD module. The conversion algorithm is identical to the algorithm used to convert local legacy modules to modules that may be loaded asynchronously when the loader is in xdomain mode. This process is fairly complex and is fully described here xxx (TODO). As far as the transform process is concerned, just like all other cases, the process results in discovering any module dependencies. Note: This process can be used as a basis for converting legacy module to AMD modules.

In summary, the transform process discovers any module dependencies through one of the following methods:

  • For known AMD modules, the module is evaluated and define/require thunks find the dependencies.
  • Legacy NLS modules are assumed to have no dependencies.
  • Modules of unknown type that do not contain legacy API applications and do contain AMD API applications are scanned with a regular expression process to find dependencies.
  • Modules of unknown type that do contain legacy API applications are processed with a regular expression process to find dependencies; the process is identical to the process used by the loader when in xdomain mode.

Once all dependencies are found, the transform ensures all dependencies exist in the discovered modules. Missing dependencies result in an error being logged to the console and the build report.

Profile Knobs

platform (default = undefined)

  • [string] The target platform when processing legacy dojo.platformRequire applications
  • [falsy] dojo.platformRequire ignores any platform-dependent dependencies

internStrings (default = undefined)

  • [truthy] Strings are interned for legacy modules.
  • [falsy] Strings are not interned for legacy modules.

internStringsSkipList (default = undefined)

  • [array of module identifiers (strings)] List of string resources to ignore during string interning.
  • [falsy] All string resources discovered during the string interning process are interned.

internSkipList (default = undefined)

  • This is a back-compat synonym for internStringsSkipList

scopeNames (default = ["dojo", "dijit", "dojox"])

  • [array of top-level module identifiers (strings)] The top-level modules names to bring into scope when executing a legacy module converted to AMD. See xxx. The vector is guaranteed to contain “dojo”, “dijit”, and “dojox”. Additional names may be added if required; however, it is highly advised that users of this feature convert their modules to proper AMD modules which eliminates the need for this feature.

scopeMap (default = undefined)

  • [map from top-level module identifier to relocated top-level module identifier (string)] The property names of scopeMap are used to populate scopeNames; the property values of scopeMap are not meaningful to the build system.

Warning: All knobs mentioned above support legacy features which are deprecated. It is strongly encouraged to convert legacy modules to properly-expressed AMD modules.

Source Location

util/build/transforms/depsScan.js

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