Improve make blogpost

blog/2020-06-08-svg-makefile-slides.md

@@ -4,20 +4,19 @@ published: 2020-06-02
 
 ---
 
-Text-based slides are boring and not effective.
-While preparing a presentation for my intermediary thesis' defence, I wanted to create something that would support my story better.
-I wanted to use graphics instead of words so the language centres of my dear audience's brains could focus on my speech rather than reading.
-Rather than importing slide-sized graphics in a GUI, I thought a makefile would be a nice way to do the trick.
+Text-based slides are boring and inefficient.
+While preparing a presentation for my intermediary thesis' defence, I wanted to use graphics instead of words so my audience wouldn't have to read and listen at the same time.
+Rather than fiddling with shapes and images in traditional office software, I knew I'd be less frustrated just using the SVG editor Inkscape.
+And a makefile would be nice to stitch the SVGs together to create a PDF file that I could use during my exposé.
 
-Makefiles these days are commonly used as a shell script with multiple entry points.
-But they can do much more than that!
+## File dependencies with makefile
+Makefiles are commonly used as a shell script with multiple entry points, but they can do much more than that!
 You give it a filename, and it will build that file if its dependencies have been changed.
-Traditionally makefiles are used for C programs, but there's no reason you can't use them for any build you want.
-Even this website is built by a makefile!
+Traditionally makefiles are used for C programs, but you can use them for absolutely any build where you have dependencies between files.
+Even this website is built by a makefile.
 Want to join me and write one together?
 
-## Writing the makefile
-Putting the name of our output file in variables will make it easier to change it later.
+Putting the name of our output file in a variable will make it to change it later, if we'd ever want that.
 ```makefile
 OUTPUT = slides.pdf
 ```
@@ -32,46 +31,70 @@ SLIDES_PDF ::= $(SLIDES:%.svg=build/%.pdf)
 
 I love this next rule.
 It teaches *make* that it should use Inkscape if it needs to create a PDF.
-`$@` refers to the target (`build/….pdf`), and `$<` refers to the first dependency (`….svg`).
 Inkscape's `--export-pdf filename` option exports to PDF without opening the GUI.
 
-**TODO: isn't there a way to automatically depend on all parent directories?**
+`$@` refers to the target (`build/….pdf`), and `$<` refers to the first dependency (`….svg`).
+
+Do note, the indentation *must* be a tab; spaces are not allowed.
+
 ```makefile
-build/%.pdf: %.svg build
+build/%.pdf: %.svg
 	inkscape --export-pdf "$@" "$<"
 ```
 
-Now we tell *make* that the final output can be created from the individual slides (`$(SLIDES_PDF)`) by calling pdfjoin.
+Next we tell *make* that the final output can be created from the individual slides (`$(SLIDES_PDF)`) by calling pdfjoin.
 
 *Make* will recursively make sure that all dependencies are up to date.
-Because we add the SVG source file as a dependency, it will know that the individual PDF files have to be rebuilt if their source was changed.
-And if any slide was changed, the end result will be updated too.
+We already declared the corresponding SVG file as a dependency for each slide's PDF, so *make* will know that it should rebuild them if the SVG was changed.
+And if any PDF was updated, the end result will be, too.
 But if there was no change, it won't; nothing is rebuilt unnecessarily!
 
-**TODO: DRY**  
+`$+` means all prerequisites, retaining duplicate entries.
+
 **TODO: Do we need to fix sh's space disease here?**
 ```makefile
 $(OUTPUT): $(SLIDES_PDF)
-	pdfjoin $(SLIDES_PDF) -o "$@"
-```
-
-If you look at the `build/%.pdf` rule, you see that it depends on `build`.
-With this rule, *make* will know how to create this directory.
-```makefile
-build:
-	mkdir -p "$@"
+	pdfjoin $+ -o "$@"
 ```
 
 It is common to create a `clean` to clean up.
-Since `clean` is not a file, we have to mark the target as "phony".
-Failing to do so would result in **TODO how to finish this sentence?**
 ```makefile
-.PHONY: clean
-
 clean:
 	rm -rf "$(OUTPUT)" build/
 ```
 
+If you now create a file `clean` and run `make clean`, *make* will quite contently say it doesn't need to do anything: the file `clean` exists and it depends on nothing else.
+To avoid this, non-file targets must be marked as "phony".
+```makefile
+.PHONY: clean
+```
+
+# Creating directories
+If you would use our makefile up to now, Inkscape would fail, complaining that `build/` doesn't exist.
+This is to be expected, since directories have to be created before you can place files in them.
+Much to my dismay, there seems to be no clean, standard way to create the necessary directories in *make*.
+In my opinion, this is *make*'s single biggest shortcoming.
+
+There [are a few ways](https://www.cmcrossroads.com/article/making-directories-gnu-make), none of them elegant.
+For our simple makefile, we can just put `@mkdir -p $(@D)` in each rule.
+It's not ideal for performance, **TODO and it might give race conditions if there are more directories and rules, should think how to word this and stuff when less tired**
+You'll have noticed by default *make* prints the commands it executes; the `@` in front of this trivial command suppresses this.
+`$(@D)` refers to the parent directory of the current target.
+
+`$(OUTPUT)` is currently defined as `slides.pdf`, but we might change it to another directory later.
+So just for good measure its rule too gets the special `mkdir` treatment.
+
+```makefile
+build/%.pdf: %.svg
+	@mkdir -p $(@D)
+	inkscape --export-pdf "$@" "$<"
+
+$(OUTPUT): $(SLIDES_PDF)
+	@mkdir -p $(@D)
+	pdfjoin $+ -o "$@"
+```
+
+# The final makefile
 One more thing: the default target, for when you call *make* without arguments, is the first one in the makefile (with [some caveats][gmake_docs_targets]).
 You could override this with `.DEFAULT_GOAL := your_target_name_here`, but it's just as easy to reorder the rules, which is what I've done in the summary below.
 
@@ -79,6 +102,9 @@ You could override this with `.DEFAULT_GOAL := your_target_name_here`, but it's
 
 This is the finished makefile:
 
+**TODO verify up to date**  
+**TODO verify actually works**
+
 ```makefile
 OUTPUT = slides.pdf
 
@@ -86,20 +112,18 @@ SLIDES ::= $(sort $(wildcard *.svg))
 SLIDES_PDF ::= $(SLIDES:%.svg=build/%.pdf)
 
 $(OUTPUT): $(SLIDES_PDF)
-	pdfjoin $(SLIDES_PDF) -o "$@"
+	@mkdir -p $(@D)
+	pdfjoin $+ -o "$@"
 
-build/%.pdf: %.svg build
+build/%.pdf: %.svg
+	@mkdir -p $(@D)
 	inkscape --export-pdf "$@" "$<"
 
-build:
-	mkdir -p "$@"
-
 .PHONY: clean
 clean:
 	rm -rf "$(OUTPUT)" build/
 ```
 
-**TODO: write about first rule being the default**  
 **TODO: split into 2 posts?**
 
 ## Further help with *make*